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+Project Gutenberg (https://www.gutenberg.org) public repository for
+eBook #55382 (https://www.gutenberg.org/ebooks/55382)
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-The Project Gutenberg EBook of Field Book of Common Rocks and Minerals, by 
-Frederic Brewster Loomis and Walter Everett Corbin
-
-This eBook is for the use of anyone anywhere in the United States and most
-other parts of the world at no cost and with almost no restrictions
-whatsoever.  You may copy it, give it away or re-use it under the terms of
-the Project Gutenberg License included with this eBook or online at
-www.gutenberg.org.  If you are not located in the United States, you'll have
-to check the laws of the country where you are located before using this ebook.
-
-Title: Field Book of Common Rocks and Minerals
-       For identifying the Rocks and Minerals of the United States
-       and interpreting their Origins and Meanings
-
-Author: Frederic Brewster Loomis
-        Walter Everett Corbin
-
-Release Date: August 18, 2017 [EBook #55382]
-
-Language: English
-
-Character set encoding: UTF-8
-
-*** START OF THIS PROJECT GUTENBERG EBOOK FIELD BOOK OF COMMON ROCKS ***
-
-
-
-
-Produced by Stephen Hutcheson, Dave Morgan and the Online
-Distributed Proofreading Team at http://www.pgdp.net
-
-
-
-
-
-
-
-
-
-                            Field Book _of_
-                              Common Rocks
-                             _and_ Minerals
-
-
-    For identifying the Rocks and Minerals of the United States and
-                interpreting their Origins and Meanings
-
-
-                                   By
-                        Frederic Brewster Loomis
-                Late Professor of Mineralogy and Geology
-                           in Amherst College
-
-
-    With 47 Colored Specimens and over 100 other Illustrations from
-         Photographs by W. E. Corbin and drawings by the Author
-
-
-                          G. P. Putnam’s Sons
-                          New York and London
-
-                               FIELD BOOK
-                                   OF
-                       COMMON ROCKS AND MINERALS
-
-                         Copyright, 1923, 1948
-                                   by
-                       Frederick Brewster Loomis
-
-                        Twenty-sixth Impression
-                              Revised 1948
-
-     All rights reserved. This book, or parts thereof, must not be
-               reproduced in any form without permission.
-
-                  Made in the United States of America
-
-
-                               Dedicated
-                                   TO
-                               MY MOTHER
-  WHO ENCOURAGED ME WHILE A BOY TO GATHER MINERALS, ROCKS AND FOSSILS.
-
-
-
-
-                                PREFACE
-
-
-Everyone, who is alert as he wanders about this world, wants to know
-what he is seeing and what it is all about. Here and there with the aid
-of capable guides a few have been introduced into the sphere of that
-wide and fascinating knowledge of Nature which has been so rapidly
-accumulated during this and the latter part of the last century. It is a
-full treasure house constantly being enriched, but unfortunately the few
-who have been initiated have soon acquired a technical language and
-habit, so that their knowledge and new acquisitions are communicated to
-but few. The public at large, not having the language nor an interpreter
-at hand, has come almost at once to a barrier which few have the time or
-patience to surmount.
-
-Latterly it has become clear that the largest progress cannot be made if
-the knowledge of any branch of Science is confined to a few only. The
-most rapid advances have been made where many men are interested and
-enthusiastic. In no science should there be a difficult barrier between
-the amateur and the professional student. All Nature is equally open for
-everyone to study, and there should never be created obstacles as by the
-use of terminology not easily acquired by anyone. Of late these barriers
-have been in part broken down and competent students have written guides
-which anyone can follow, and soon begin to know the plants, trees,
-birds, insects, etc. So far no one has attempted to make the study of
-minerals and rocks so direct and simple that everyone can get a start.
-Most books on minerals, and practically all those on rocks are written
-for school courses, and to say the least chill any enthusiasm which is
-naturally aroused by the finding of interesting looking rocks or
-minerals.
-
-The purpose of this book is first of all to provide a means of
-identifying minerals and rocks by such methods as are practical without
-elaborate equipment or previous training: and second to suggest the
-conditions under which the various minerals and rocks were formed, so
-that, at the first contact, one may get a conception of the events which
-have anteceded the mineral or rock which has been found. For this
-purpose keys have been worked out for determining the rocks and minerals
-by such obvious features as color, hardness, etc. Each mineral or rock
-is introduced by a summary of its characters, then the features by which
-it may be distinguished from any other similar mineral are given, after
-which its mode of origin and its meanings are considered. For those
-interested in the composition of the minerals, it is given in chemical
-symbols with each mineral. Most classifications of minerals are based on
-the composition, all the sulphides, carbonates, etc., being grouped
-together, but in this book, because the popular interest and commercial
-uses are primarily in the metal present, the minerals are grouped in
-each case about the chief metal, all the minerals of iron being grouped
-together, for instance.
-
-A few minerals and rocks which are not strictly common have been
-included such as gems and meteorites; the gems because they are of
-intense interest to their owners and are often simply perfect examples
-of a fairly common mineral; and such forms as meteorites because it is
-important that, if one should run across one, it should be recognized,
-and so not lost to the world.
-
-The book is freely illustrated, those minerals in which color is
-important for identification being illustrated in colors, and those
-which are black, or in which the color is not a determining factor, are
-shown in either photographic or outline figures.
-
-In the introductory chapter there are explanations of the terms used in
-describing minerals, and of the systems in which they are grouped. A
-knowledge of the systems may not be a necessity, but it is a great help
-in determining minerals, and is very important in understanding why the
-individual minerals take the varied forms which are characteristic of
-them. These systems will be better understood after a few minerals have
-been gathered and examined.
-
-It is hoped the book will help those who have already some knowledge of
-rocks and minerals, and especially that it will tempt many to begin an
-acquaintance with the rocks and minerals which are all about them, and
-are the foundation on which our material progress is built. Rocks and
-minerals have some advantages over most objects which are collected in
-that they neither require special preparation before they can be kept,
-nor do they deteriorate with time.
-
-The author will appreciate corrections or suggestions as to better
-presentation of the material in this book.
-
-                                                                F. B. L.
-
-Amherst, Mass.
-
-
-
-
-                                CONTENTS
-
-
-                                                                     PAGE
-  Preface                                                             vii
-  CHAPTER
-  I.—An Introduction                                                    3
-  II.—On the Forms and Properties of Minerals                          10
-  III.—The Minerals                                                    25
-  IV.—The Rocks                                                       170
-  V.—Miscellaneous Rocks                                              248
-   Bibliography                                                       270
-   Index                                                              273
-
-
-
-
-                             LIST OF PLATES
-                            (AT END OF BOOK)
-
-
-                                                                     PAGE
-  Tourmaline crystals, growing amid feldspar crystals in a cavity in
-          granite, from Paris, Me.                                    279
-  Plate 1.—Basal forms of the isometric system                        311
-  Plate 2.—Basal forms of the tetragonal system. Basal forms of the
-          orthorhombic system                                         312
-  Plate 3.—Basal forms of the monoclinic system. A cross section of
-          the prism with its edges beveled so that a six-sided prism
-          is formed (pseudo-hexagonal). Basal form of the triclinic
-          system.                                                     313
-  Plate 4.—Basal forms of the hexagonal system                        314
-  Plate 5.—Gold in quartz from California (_in color_)                280
-  Plate 6.—Native silver in calcite. Argentite, the black masses
-          throughout the white quartz (_in color_)                    281
-  Plate 7.—Pyrargyrite as it appears after moderate exposure to the
-          light; streak at left. Crystal form of pyrargyrite.
-          Prousite as it appears after moderate exposure to the
-          light; streak at left (_in color_)                          282
-  Plate 8.—Native copper from Michigan. Chalcopyrite in tetrahedrons
-          and an occasional octahedron; streak to the left (_in
-          color_)                                                     283
-  Plate 9.—Chalcocite crystals with the bluish tarnish. Tetrahedrite
-          crystals; streak to left (_in color_)                       284
-  Plate 10.—Tetrahedrons showing characteristic manner in which
-          tetrahedrite occurs. A cube with the edges beveled and the
-          corners cut in a form characteristic of cuprite             315
-  Plate 11.—Cuprite, the red crystals showing characteristic color,
-          others showing the green tarnish of malachite. Malachite
-          (green) and azurite (blue), the two minerals shown
-          together as they very commonly occur (_in color_)           285
-  Plate 12.—Limonite. The crystal form in which goethite is found
-          (_in color_)                                                286
-  Plate 13.—Hematite. Clinton iron ore, oolitic. Siderite crystals
-          (_in color_)                                                287
-  Plate 14.—Crystal forms of hematite. A typical crystal of
-          magnetite. The rhombohedron typical of siderite             317
-  Plate 15.—Pyrite crystals. Marcasite in concretionary form with
-          radiate structure (_in color_)                              288
-  Plate 16.—The pyritohedron. The pyritohedron with certain of its
-          edges beveled by the cube faces, to show the relationship
-          of these two forms                                          318
-  Plate 17.—Galena in crystals. Pyromorphite crystals (Green) (_in
-          color_)                                                     289
-  Plate 18.—Typical forms for cerrusite. Forms in which anglesite
-          occurs                                                      319
-  Plate 19.—Sphalerite, some the normal yellow and some crystals
-          with the reddish tinge. (White is dolomite.) Zincite,
-          streak to the left (_in color_)                             290
-  Plate 20.—A characteristic form in which sphalerite may occur.
-          Characteristic form for zincite crystals. Typical form of
-          crystal of willemite                                        320
-  Plate 21.—Smithsonite in yellow crystals. Franklinite in
-          octahedral crystals, streak to left (_in color_)            291
-  Plate 22.—Moss agates, showing the dendritic growth of manganitic
-          minerals, like manganite or pyrolusite. Crystal form of
-          manganite                                                   321
-  Plate 23.—Crystals of green corundum in syenite, from Montana.
-          Typical crystal forms of corundum                           322
-  Plate 24.—Arsenopyrite, showing crystals massed so as to be
-          incompletely developed. Realgar as it usually occurs in
-          powdery incrustations (_in color_)                          292
-  Plate 25.—Large crystals of stibnite; the light colored face is
-          the one parallel to which cleavage occurs. Niccolite is a
-          vein in slate (_in color_)                                  293
-  Plate 26.—Cobaltite, silver color, with pink tinge. Smaltite, pink
-          is cobalt bloom (_in color_)                                294
-  Plate 27.—Carnotite from Southwest Colorado. Cinnabar (_in color_)  295
-  Plate 28.—Cassiterite, twinned crystals. The crystal form in which
-          both cassiterite and rutile occur when in simple crystals.
-          Multiple twinning characteristic of rutile                  323
-  Plate 29.—Crystal of spinel. Crystal forms in which dolomite
-          occurs                                                      324
-  Plate 30.—Two intergrowing or twinned quartz crystals. Diagram of
-          the typical quartz crystal. A quartz crystal on which the
-          left hand rhombohedron is represented by small faces,
-          while the right hand rhombohedron has large faces           316
-  Plate 31.—Amethyst, not however deep enough colored for gems.
-          Jasper, with botryoidal surface (_in color_)                296
-  Plate 32.—Banded agate from Brazil (_in color_)                     297
-  Plate 33.—Common opal from Arizona. Siliceous sinter or geyserite
-          from Yellowstone Park (_in color_)                          298
-  Plate 34.—Orthoclase, a cleavage piece. Crystal forms of
-          orthoclase. Diagram of a multiple twin of a plagioclase
-          feldspar                                                    325
-  Plate 35.—A group of microcline crystals from Pike’s Peak, Colo.
-          Labradorite, showing multiple twinning (the striation) and
-          the iridescent play of colors (_in color_)                  299
-  Plate 36.—Crystal form of a pyroxene. Cross sections of a pyroxene
-          crystal showing the lines of intersection of two cleavage
-          planes. Cross sections of pyroxenes, showing typical forms
-          taken by crystals. Augite crystals, in crystalline
-          limestone (_in color_)                                      300
-  Plate 37.—Diagrams of amphibole crystals. Tremolite in silky
-          fibrous crystals, asbestos. Hornblende crystals in
-          quartzite                                                   326
-  Plate 38.—The dodecahedron and the 24-sided figure characteristic
-          of garnets. The garnet, grossularite. The garnet,
-          alamandite (_in color_)                                     301
-  Plate 39.—Beryl of gem quality. Zircon in syenite (_in color_)      302
-  Plate 40.—Cyanite crystals in schist. A crystal of mica, showing
-          basal cleavage (_in color_)                                 303
-  Plate 41.—Crystal form typical of topaz. A topaz crystal from
-          Brazil. Crystal form typical of staurolite when simple. A
-          typical twin of staurolite (_in color_)                     304
-  Plate 42.—Epidote crystals. Typical forms of epidote crystals.
-          Typical forms of tourmaline                                 327
-  Plate 43.—Serpentine. Chlorite (_in color_)                         305
-  Plate 44.—The typical form of analcite. A typical natrolite
-          crystal. The typical crystal form of stilbite. A
-          sheaf-like bundle of fibrous crystals, typical of stilbite  329
-  Plate 45.—A group of calcite crystals. Typical forms of calcite     330
-  Plate 46.—Typical forms of aragonite. Typical form of the
-          anhydrite crystal                                           331
-  Plate 47.—A piece of gypsum looking on the surface of the perfect
-          cleavage, and showing the two other cleavages as lines,
-          intersecting at 66°. Twinning is also shown. A simple
-          crystal of gypsum. Twin crystals of gypsum.                 332
-  Plate 48.—A group of barite crystals. Outline of the typical
-          tabular barite crystal. The six-sided double pyramid,
-          composed of three interpenetrating crystals, typical of
-          witherite and strontianite                                  328
-  Plate 49.—Apatite crystals in crystalline calcite. The ends of
-          apatite crystals showing common modes of termination (_in
-          color_)                                                     306
-  Plate 50.—A group of fluorite crystals. A group of halite crystals
-          (_in color_)                                                307
-  Plate 51.—Sulphur crystals. Ice crystals, the top one, the end of
-          a hexagonal prism; the two lower figures multiple twins as
-          in snow flakes                                              333
-  Plate 52.—The Devil’s Tower, Wyoming, an example of igneous rock
-          with columnar structure, and resting on sedimentary rocks   334
-      Courtesy of the U. S. Geological Survey
-  Plate 53.—A coarse granite. Graphic granite                         335
-  Plate 54.—Syenite. Gabbro                                           336
-  Plate 55.—Basalt-porphyry. The large white crystals are
-          phenocrysts of plagioclase feldspar. Basalt-obsidian        337
-  Plate 56.—Amgydoloid                                                338
-  Plate 57.—The north face of Scott’s Bluff, Neb., showing
-          sedimentary sandstones above and clays below. The type of
-          erosion is characteristic of arid regions                   339
-      Courtesy of the U. S. Geological Survey
-  Plate 58.—Breccia. Conglomerate                                     340
-  Plate 59.—Calcareous shale. Coquina                                 341
-  Plate 60.—Foramenifera from chalk; enlarged about 25 diameters.
-          Encrinal limestone; fragments of the stems, arms and body
-          of crinoids                                                 342
-  Plate 61.—Amber. Two bottles of petroleum, the left hand one with
-          a paraffin base, the right hand one with an asphalt base
-          (_in color_)                                                308
-  Plate 62.—Diatomaceous earth magnified 50 times. Two diatoms from
-          the above enlarged 250 times                                343
-      After Gravelle, by the courtesy of Natural History
-  Plate 63.—A metamorphic rock, showing the contortion of layers due
-          to expansion under heat                                     344
-  Plate 64.—A conglomerate partly metamorphosed to a gneiss. A
-          typical gneiss                                              345
-  Plate 65.—Mica schist, with garnets. Chlorite schist (_in color_)   309
-  Plate 66.—Phyllite. A white marble, with black streaks due to
-          graphite                                                    346
-  Plate 67.—Serpentine composed of serpentite, hematite, and some
-          calcite (_in color_)                                        310
-  Plate 68.—Claystones, simple and compound. A lime concretion,
-          which on splitting disclosed a fern leaf of the age of the
-          coal measures                                               347
-  Plate 69.—A septeria from Seneca Lake, N. Y. Pisolite from Nevada   348
-  Plate 70.—A geode filled with quartz crystals                       349
-  Plate 71.—A quartz pebble from the bed of a New England brook. A
-          pebble of schist and granite from the foot of Mt. Toby,
-          Mass.                                                       350
-  Plate 72.—An iron-nickel meteorite, of 23 lbs., which fell in
-          Claiborne Co., Tenn. An etched slice of an iron meteorite
-          which fell in Reed City, Osceola, Co., Mich.                351
-  Plate 73.—A stone meteor, about natural size, which fell in 1875
-          in Iowa Co., Iowa                                           352
-
-
-
-
-                             FIELD BOOK OF
-                       COMMON ROCKS AND MINERALS
-
-
-
-
-                               CHAPTER I
-                            AN INTRODUCTION
-
-
-Why
-
-Why should one be interested in rocks and minerals? Because the whole
-world is made of rocks and minerals. They are the foundations on which
-we build. From them we draw all our metals, and the extent to which we
-utilize our minerals is a measure of the advance of our civilization.
-Fragments of rock are the soil from which, by way of the plants, we draw
-our food, and ultimately our life. The rocks make wild or gentle
-scenery, one at least of the sources of pleasure. Knowledge of rocks and
-minerals is then knowledge of fundamentals, of ultimate sources. Between
-finding the raw materials and their present uses there are usually many
-steps (so many that we forget that the beginning and end are united), as
-for instance in your watch. It is made of gold, brass, steel, agate,
-glass, and perhaps has luminous radium paint on the hands. It is a long
-way from finding and mining gold, chalcopyrite, hematite, carnotite,
-etc., through the raw materials, gold, copper, iron, etc., to the
-finished watch, but the minerals are the foundations of the watch; and
-it took centuries to find them and learn one by one how to use them,
-from the gold 10,000 years ago down to the radium within the last fifty
-years. Then too there is joy in going out into Nature’s wild and raw
-places, joy in being on the foundations of the earth, joy in the
-scenery, in the beauty of the minerals themselves.
-
-But why collect the rocks and minerals? First because this is the way to
-know them. Both mineral and rocks require careful examination in order
-to see all those fine points by which they are distinguished. It is
-often necessary to compare one with another to get in mind the
-differences of form, color, streak, though with increasing familiarity
-these characteristics are recognized at first sight. It is the repeated
-examination which makes a rock tell the story of the country from which
-it came. Our first attempts to read the story give us only the most
-general facts. Nature’s book, written in the rocks, has to be read
-closely, often between the lines. Until we are used to the characters in
-which the words are written, we read slowly. When they look at Nature’s
-book, always open, most people do not read; for they do not know their
-letters. Every mineral is a letter, every rock a word, and we learn to
-read as we learn the minerals and rocks, and every time we go over them
-we get more facts coming out. The place where a rock or mineral occurs
-is of course the relation between them, and is involved in reading the
-story. No one today is a perfect reader. We are all learning to see more
-in the rocks day by day. So it is important to have the rocks and
-minerals where they can be handled and repeatedly examined, where we can
-turn to them in our leisure moments. Don’t stop when you have learned
-the name of a mineral or rock. You need more. See what it means.
-Secondly, minerals have beauties of form, color, and structure, and they
-do not fade. They will be as perfect in ten years as when found. We are
-all naturally crows, and love to gather the objects which interest us.
-It is not a bad habit, and only needs directing. Cultivate it. Have a
-hobby, and minerals and rocks are a good one; for they are like
-treasures in Heaven which “neither moth nor rust doth corrupt.” Not only
-will they give you pleasure, but they will be a constructive education,
-training the eye to see, and the mind to think straight. No one ever
-regretted the time and effort spent in collecting either minerals or
-rocks.
-
-
-Collecting
-
-In order to make a collection valuable two or three rules must be
-observed. In the case of rocks, collect large enough samples so that
-they will be characteristic, and clear in their make-up. The standard
-size for rocks is 3 × 4 inches on top and one to two inches thick
-according to the nature of the rock. Tiny fragments do not give the
-character of the rock as well, and they are all the time getting into
-confusion. Every specimen should be labeled, with at least its name and
-the exact locality from which it came. Composition, structural features,
-associations, and classification may be added, the more the better; for
-each item adds to the information and interest of the specimen. One may
-make his own labels or have printed blanks, and may put as much care and
-art into the labels as desired, the more the better. One thing is very
-important and that is to have a number on the label with a corresponding
-one on the specimen, so that in case they should get separated, they may
-be readily brought together, even by one who is not familiar with the
-individual specimens. Lastly, give your collection as good a place as
-possible, either in drawers, boxes or in a case. The specimens are worth
-being kept in order and where they can be readily seen and compared.
-Nature is systematic, and there is a reason for the order in which rocks
-and minerals are taken up. It is desirable either that this order, or
-some one of the orders of Nature appear in the collection. In this book
-the metals are the basis of classification, all those minerals primarily
-related to one of the metals being grouped together.
-
-In collecting minerals, the size of the specimens can not be so
-regularly followed, but it should be followed when collecting
-non-crystalline minerals, and when possible. Crystals however are chosen
-from a variety of points of view, as perfection of form, color, examples
-of cleavage, twinning, etc.; so that in many cases smaller or larger
-examples must appear in the collection. It is always desirable that as
-many variations of a rock or mineral as possible should appear in the
-collection, and in many cases examples of the matrix from which the
-crystals came. When crystals are tiny, it is well to place them in
-vials, that they may not be lost.
-
-
-Where
-
-Where shall we start in making a collection? Near home. Get the local
-minerals and rocks first, and then range as widely as possible. The best
-places are bare and exposed rocks, especially where fresh and
-un-weathered surfaces are available. Quarries and where there has been
-blasting along roads offer fine opportunities. Fissures and cavities in
-the rocks are especially likely to have fine crystals, and in all
-localities continued search will reveal a surprising number of different
-minerals. The greatest variety occur in metamorphic rocks, or where
-igneous rocks come in contact with other rocks, but even the sedimentary
-rocks have a goodly range of minerals. All through the glaciated regions
-of the northern United States lie scattered boulders brought from afar,
-which will yield a surprising number of minerals and variety of rocks.
-
-
-Equipment
-
-One may start with a very simple equipment, a geologist’s or stone
-mason’s hammer which can be obtained at any hardware store, being
-sufficient for field work. Rocks should be broken, so as to show fresh
-surfaces and to get below the disintegrating effects of weathering. At
-home one should have a streak plate (a piece of unglazed porcelain), a
-set of hardness minerals (see page 20), and a small bottle each of
-hydrochloric and nitric acid. A pocket lens is useful in order to see
-more clearly the form of small minerals. These things can be purchased
-of any Naturalist’s Supply Co., like Ward’s Natural Science
-Establishment, P.O. 24, Beachwood Sta., Rochester, N. Y., or the
-Kny-Scheerer Corp., 483 First Ave., New York City. Success depends upon
-a quick eye, and persistent hunting. When traveling, opportunities are
-offered at frequent intervals to see and get new specimens.
-
-
-Study Your Collection
-
-Be sure and see the meaning in each rock and mineral. The history of the
-country is revealed in its rocks and minerals. Note whether the rocks
-are horizontal or folded, whether they change character from place to
-place, or vertically. In going over a piece of country you may locate an
-ancient mountain system now leveled, by noting a series of metamorphic
-rocks, with a central core of granite, the roots of former mountains.
-Don’t be afraid to draw conclusions from what you see. Later, when the
-opportunity offers, look up the region in the geological folio,
-bulletin, or map of that section, and check up your findings. These
-geological folios and bulletins, of which there is one for nearly every
-region, are a great help to collectors in suggesting where to look for
-various rocks and minerals. Write to the Director of the U. S.
-Geological Survey, Washington, D. C., for a catalogue of the
-publications of the United States Survey, or find out from him what are
-the maps or folios for the region in which you are interested. These U.
-S. publications cost but little. When opportunity presents itself, visit
-other collections. In them you will see some of the minerals or rocks
-which have puzzled you, and there is nothing quite so satisfactory as
-seeing the rocks or minerals themselves. No description can always be so
-convincing. Then too you will get suggestions as to localities that you
-can visit.
-
-
-Literature
-
-As your collection grows, if you find you have special interest in one
-or another branch of the field, you can get books giving more details in
-that line; and at the back of this book will be found a list of such
-books.
-
-
-
-
-                               CHAPTER II
-                ON THE FORMS AND PROPERTIES OF MINERALS
-
-
-Rocks
-
-All we know of the earth by direct observation is confined to less than
-four miles depth; though by projecting downward the layers of rock that
-come to the surface, we may fairly assume a knowledge of the structure
-down to six or eight miles depth. This outer portion is often referred
-to as the “crust of the earth,” but the idea that the deeper portions
-are molten is no longer held. This outer portion is made of rocks, and a
-rock may be defined as, _a mass of material, loose or solid, which makes
-up an integral part of the earth_, as granite, limestone, or sand. The
-rocks (except glassy igneous ones) are aggregates of one or more
-minerals; either in their original form like the quartz, feldspar and
-mica of granite, or in a secondary grouping, resulting from the units
-having been dislodged from their primary position and regrouped a second
-time, as in sandstone or clay.
-
-
-Minerals
-
-Since the rocks are aggregates of minerals, it is best to take up the
-minerals first. A mineral may be defined as _a natural inorganic
-substance of definite chemical composition_. It is usually solid,
-generally has crystalline structure, and may or may not be bounded by
-crystal faces. _A crystal is a mineral, bounded by symmetrically grouped
-faces, which have definite relationships to a set of imaginary lines
-called axes._ There are between 1100 and 1200 minerals, of which 30 are
-so frequently present, and so dominant in making up the rocks, that they
-are termed _rock-forming minerals_. About 150 more occur frequently
-enough so that they can be termed common minerals, and one may expect to
-find a fairly large proportion of them. Some of these are abundant in
-one part of the country and rare in others, but this book is written to
-cover the United States, and so all those which have a fair abundance
-are included, though some will only be found in the west and others
-mostly in the east. Then there are some more minerals which are really
-rare, but which are cherished because of their beauty of color, and are
-used as gems. These are mentioned, and many of the gems are simply clear
-and beautiful examples of minerals, which in dark or cloudy forms are
-much more common. If one finds any of these rare minerals which are not
-mentioned in this book, he must turn to one of the larger mineralogies
-mentioned in the literature list to determine them.
-
-
-Crystal Structure
-
-A crystal is a mass of molecules, all of the same composition. A
-molecule in its turn is made up of atoms, and each atom is a unit mass
-of an element. Thus the calcite molecule is made up of one unit or atom
-of calcium, one of carbon, and three of oxygen (CaCO₃). These atoms are
-held together by an attraction, and make a molecule, and for the study
-of minerals the molecule is the unit. The mineral, calcite, is a mass of
-molecules all like the one above, and each molecule so small as to be
-invisible even with the aid of the most powerful microscope. When
-calcite is in crystal form, the molecules, like ranks of soldiers, are
-arranged each in its place, each at a definite distance from the other.
-While each molecule may vibrate or wiggle within certain limits it does
-not leave its place. (The comparison with soldiers is a good one for the
-molecules of one layer, but it must be remembered that in a crystal
-there are also like spacings and ranks up and down as well.) As long as
-the molecules remain in fixed ranks, up and down, forward and back, and
-sideways, the crystal is perfect. Calcite may be heated until it melts
-and becomes liquid. Then the molecules leave their definite arrangement
-and move about in all sorts of directions, like the soldiers after ranks
-have broken. So long as the molecules are thus free to move about but
-keep together, the substance is a liquid. There are cases when the
-molecules in this disorder take fixed positions without falling into
-ranks. Such minerals are non-crystalline and usually appear glassy. If
-still greater heat is applied to the mineral in liquid form, a point is
-reached (the vapor point), above which the molecules go flying away from
-each (like soldiers in a panic), each seeking to get as far from the
-other as possible, so only a container will prevent their dissipation.
-When in this condition a mineral is gaseous. When cooled, the reverse
-order obtains. The molecules of gas gather into a miscellaneous mob or
-liquid: and if this is further cooled (but not too suddenly), they fall
-into ranks and make a crystal. This may be illustrated with water. When
-above 212° F. it is steam (molecules wildly dissipated); when between
-212° and 32° it is water (molecules close to each other, but milling
-like a herd of cattle); and when below 32° it is ice, the molecules
-ranged in perfect order, rank on rank.
-
-
-Crystal Systems
-
-With all the possible forms that crystals can and do take, there are six
-systems of arrangement. First there is the case where ranks, files, and
-vertical rows are all equal, and now to be scientific, instead of
-talking about ranks, files, etc., we use the term axes to express these
-ideas; the files or arrangements from front to back, being called the _a
-axis_, the ranks, or side to side arrangement the _b axis_, and the
-vertical arrangement the _c axis_. (See Plate 1.) These axes are
-imaginary lines, but they represent real forces.
-
-
-Isometric system
-
-When the axes are all equal and at right angles to each other, a crystal
-is said to be in the isometric system. The cube is the basal form and
-each side is known as a face. The ends of the axes come to the middle of
-the cube faces. The essential feature of this system is that whatever
-happens to one axis must happen to all, which is another way of saying
-that all the axes are equal. If we think of the cube as having the
-corners cut off, we would have a new face on each of the eight corners,
-in addition to the six cube faces. Then if each of these new faces were
-enlarged until they met and obliterated the cube faces, an eight-sided
-figure, the octahedron, would result. In this the axes would ran to the
-corners. Another modification of the cube would be to bevel each of its
-twelve edges, making twelve new faces in addition to the six cube faces.
-If we think of these new faces being developed until they meet and
-obliterate the cube faces, there will result a twelve-sided figure, the
-dodecahedron. And the 24 edges of the dodecahedron could be beveled to
-make a 24-sided figure, and so on. Of course in Nature the corners are
-not cut, nor the edges beveled, but as a result of the interaction of
-the forces expressed by the axes and the distribution of the molecules,
-the molecules arrange themselves in a cube, octahedron, dodecahedron or
-combination of these basal forms.
-
-
-Crystal formation
-
-Crystals are formed in liquids as they cool or evaporate and can no
-longer hold the minerals in solution. Crystals start about a center or
-nucleus, and molecule by molecule, the orderly arrangement is increased
-and the crystal grows, there being no size which is characteristic. If
-free in the liquid the crystal grows perfectly on all sides, but if
-crystals are growing side by side, there comes a time when they
-interfere with each other. Then the free faces continue to grow and the
-orderly internal arrangement is maintained, though externally there is
-interference.
-
-
-Tetragonal system
-
-In the second or tetragonal system one axis (the c axis) is different
-from the other two, but all three are still at right angles with each
-other. This is saying scientifically that the lines of force are greater
-or less in one direction than in the other two, but they act at right
-angles to each other. The a and the b axes are equal and anything that
-happens to one of these two must happen to the other, but need not
-happen to the c axis. Thinking of the molecules that arrange themselves
-under this system of forces, it is clear that the simplest form will be
-a square prism, _i.e._, front to back, and from side to side the numbers
-of molecules will be equal, but up and down there will be a greater or
-lesser number. If the eight corners of this prism were cut, and these
-corner faces increased in size until they met, the resulting octahedron
-would be longer (or shorter) from top to bottom than from side to side
-or front to back, but the measurement from front to back would be equal
-to the one from side to side. In this system we may have the vertical
-edges of the prism beveled, and not have to bevel the horizontal ones,
-or we may bevel the horizontal edges and not the vertical ones. There is
-no dodecahedron in this system or in any other system than the
-isometric. The forms in this tetrahedral system are really a combination
-of the four sides of the square prism with such modifications as equally
-affect them all, with two ends which may be flat, or pyramidal, or
-modified pyramidal faces.
-
-
-Orthorhombic system
-
-The third system has all three axes unequal, but all three are still at
-right angles with each other. This is saying that the lines of force in
-the crystals are all at right angles to each other but of unequal value.
-The faces in this case are all in pairs. What happens at one end of an
-axis must happen at the opposite end, but does not need to happen at the
-ends of any of the other axes. We are dealing with pairs of faces (one
-at either end of an axis), and if three such pairs are combined in the
-simplest manner, the resulting figure will be a rectangular prism. If we
-cut the eight corners of this prism and enlarge the faces until they
-meet, the result is an octahedron, in which the distance from top to
-bottom, from side to side, or from front to back is not the same in any
-two cases. (See Plate 2.) In this system if a face is made by beveling
-one edge of the prism there must be a corresponding face on the edge
-diagonally opposite, but there does not have to be one on any of the
-other edges. However if a corner is cut, that face affects all the axes
-and so all the corners must be cut. A great many crystals occur in this
-system, and some of them which are prismatic in shape may give trouble,
-for it is not uncommon for the vertical edges of the prism to be so
-beveled, that two of the original prism faces are obliterated, and the
-two remaining faces added to the four new faces make a six-sided prism,
-which at first glance seems to belong to the hexagonal system. (See
-Plate 3, fig. 3.) Close examination however will show that, instead of
-all the prism faces being alike, as would be necessary for the hexagonal
-system, they are really in pairs, and one pair at least will be
-distinguished in some way, such as being striated, pitted, or duller.
-
-
-Monoclinic system
-
-The fourth system has all the axes unequal, the a axis and the b axis at
-right angles to each other, but the c axis is inclined to the a axis,
-meeting it at some other than a right angle. The monoclinic system is
-like the orthorhombic system except that it leans, or is askew, in one
-direction. The result is that the faces at the ends of the b axis are
-rhombohedral, while the others are rectangular. As in the foregoing
-system, the faces are in pairs at opposite ends of the axes; and as in
-the orthorhombic system, a face may occur on one edge and only have to
-be repeated on the edge diagonally opposite. The simplest form in this
-system will be made by combining the three pairs of faces at the
-opposite ends of the axes, which gives a prism, which is rectangular in
-cross section, but leans backward (or forward) if placed on end. As in
-all the systems, if a corner is cut, all must be cut; and if these
-corner faces are extended to meet each other, an octahedron results, in
-which, as in the prism, no two axes are equal. If this octahedron is
-properly orientated (_i.e._ with the a and b axes horizontal), it will
-lean forward or backward. Many minerals belong to this system; and, as
-in the orthorhombic system, it is not uncommon to have the vertical
-edges so beveled that two of the prism faces are obliterated, and the
-remaining two prism faces with the four new faces make a six-sided
-prism, which seems hexagonal. (See plate 3, figure 3.) However, such a
-pseudo-hexagonal prism may be recognized by at least one pair of the
-faces having distinguishing marks (striæ, pits, or dullness), instead of
-all being just alike.
-
-
-Triclinic system
-
-The fifth or triclinic system has all the axes unequal, and no two of
-them intersect at right angles. As in the two preceding systems the
-faces occur in pairs at the opposite ends of the axes. This is the most
-difficult system in which to orientate a crystal, but fortunately only a
-few crystals occur in this system, such as the feldspars.
-
-
-Hexagonal system
-
-Lastly there is a group of crystals which have four axes, one vertical,
-and three in the horizontal plane which intersect each other at angles
-of 60°, all these three being equal to each other, but different from
-the vertical axis. The simplest form in this system is the six-sided
-prism. If one corner of this prism is cut all must be, and if these
-corner faces are extended to meet each other, a double-six-sided pyramid
-results. In this system if one of the vertical edges of the prism is
-beveled, all must be, but the horizontal edges need not be; or the
-horizontal edges may be beveled and the vertical ones not. The ends as
-they are related to the c axis may be developed independently of the
-prism, and so the prism may be simply truncated by a flat end, or have
-pyramids on either end.
-
-
-Hemihedral forms
-
-In this system it is quite common to have forms which result from the
-development of each alternate face of either the prism or the double
-pyramid. In the case of the prism, if every alternate face is developed
-(and the others omitted) a three-sided prism results, as in tourmaline.
-In the case of the double pyramid if the three alternate faces above are
-united with the three alternate faces below, a six-sided figure is
-formed, which is known as the rhombohedron, as all the faces are
-rhombohedral in out-line and all equal. These forms in which only half
-the faces are developed are known as hemihedral forms. The same sort of
-thing may happen in the isometric system in the case of the octahedron,
-and also in the case of the octahedron of other systems. When half the
-faces of the octahedron are developed, two above unite with two below
-and make a four-sided figure, known as a tetrahedron. (See plate 10.)
-While tetrahedrons may occur in any of the first five systems they are
-not common outside the isometric system.
-
-
-Twinning
-
-Another modification of the simple forms which will be met occasionally
-is twinning. By this is meant two crystals growing together as though
-placed side by side on some one of the faces, and then revolved until
-the two axes which would normally be parallel are at some definite angle
-with each other, 60°, or 180° which is commoner. The surface of contact
-between the two crystals is called the _composition face_, and as no
-more material can be added on that face the crystals continue to grow
-developing the other faces, and we find faces in contact with each other
-which should be at the opposite end or other side of the crystals. This
-contact of faces which should not come in contact, and the presence of
-reentrant angles are indications of twinning. In some minerals the
-twinning may be repeated time and again, and if the twinning is on one
-of the end faces a branching structure results, as in frost and snow
-crystals, or the multiple twinning may be of crystals growing side by
-side when the final form will approximate a series of thin sheets placed
-side by side as in some feldspars. The peculiar forms characteristic of
-individual minerals are taken up under the respective minerals.
-
-Other important properties of minerals are hardness, cleavage, specific
-gravity, streak, luster, and color.
-
-
-Hardness
-
-Hardness may be defined as the mineral’s resistance to abrasion or
-scratching. It is measured by comparing a mineral with Moh’s scale, a
-set of ten minerals arranged in the order of increasing hardness, as
-follows:
-
-  1 talc
-  2 gypsum
-  3 calcite
-  4 fluorite
-  5 apatite
-  6 feldspar
-  7 quartz
-  8 topaz
-  9 corundum
-  10 diamond
-
-A set for measuring hardness may be purchased from any dealer in mineral
-supplies. For rough determination, as in the field, the following
-objects have the hardness indicated; the finger nail 2¼, a penny 3, a
-knife blade about 5.5, and glass not over 6. In testing, a mineral is
-harder than the one it will scratch, and softer than the one by which it
-is scratched. For instance, if a mineral will scratch calcite and is
-scratched by fluorite, it is between 3 and 4 in hardness, say 3.5. When
-two samples mutually scratch each other they are of equal hardness. Care
-must be used in determining hardness, especially with the harder
-minerals; for often, when testing a mineral, the softer one will leave a
-streak of powder on the harder one, which is not a scratch. One should
-always rub the mark to make sure it is really a groove made by
-scratching.
-
-
-Cleavage
-
-Cleavage is the tendency, characteristic of most minerals, and due to
-the arrangement of their molecules, to cleave or break along definite
-planes. The cleavage of any mineral is not irregular or indefinite, but
-characteristic for each mineral, and always parallel to possible or
-actual faces on the crystal, and always so described. For instance
-galena has three cleavages, all equally good, and parallel to the cube
-faces; so it is said to have cubic cleavage. In the same way fluorite
-has octahedral cleavage, and calcite rhombic cleavage. In some minerals
-cleavage is well developed in one plane, and less developed in other
-planes, or it may be lacking altogether. The varying degrees of
-perfection by which a mineral cleaves are expressed as, perfect or
-imperfect, distinct or indistinct, good or poor, etc.
-
-
-Specific gravity
-
-The specific gravity of a mineral is its weight compared with the weight
-of an equal volume of water, and is therefore the expression of how many
-times as heavy as water the mineral is. For instance the specific
-gravity of pyrite is 5.1, which is saying it is 5.1 times as heavy as
-water. In a pure mineral the specific gravity is constant, and an
-important factor in making final determinations. As ordinarily obtained,
-a piece of pure mineral is weighed in air, which value may be called x.
-It is then immersed in water and again weighed, and this value is called
-y. The difference between the weight in air and that in water is the
-weight of an equal volume of water. Then we have the following formula:
-
-                     specific gravity = (x)/(x-y).
-
-Various balances have been devised for making these measurements, but
-any balance which will weigh small objects accurately, may be adapted to
-specific gravity work, by hanging a small pan under the regular weighing
-pan. When using this balance, care is taken to see that the lower pan is
-always submerged in water, even while the mineral is being weighed in
-air, so that when weighed in water in the lower pan, the weight of this
-lower pan has already been considered.
-
-
-Streak
-
-By streak is meant the color of the mineral when powdered. For some
-minerals, especially metallic ores, it is of great importance, for it
-remains constant, though the color of the surface of the mineral changes
-materially. It is most readily determined by rubbing a corner of the
-mineral on a piece of unglazed porcelain. Small plates, known as “streak
-plates” are made for this purpose.
-
-
-Luster
-
-The luster of a mineral is the appearance of its surface by reflected
-light, and it is an important aid in determining many minerals. Two
-types of luster are recognized; metallic, the luster of metals, most
-sulphides and some oxides, all of which are opaque on their thin edges;
-and non-metallic, the luster of minerals which are more or less
-transparent on their thin edges, and most of which are light colored.
-The common non-metallic lusters are; vitreous, the luster of glass;
-resinous, the appearance of resin; greasy, oily appearance; pearly, the
-appearance of mother-of-pearl; silky, like silk due to the fibrous
-structure; adamantine, brilliant like a diamond; and dull, as is chalk.
-
-
-Color
-
-When used with caution color is of the utmost importance in determining
-minerals, especially in making rapid determinations. In metallic
-minerals it is constant and dependable; but in the non-metallic minerals
-it may vary, due to the presence of small amounts of impurities which
-act as pigments. Color depends on chemical composition, and when not
-influenced by impurities is termed _natural_; but when the color is due
-to some inclosed impurity it is termed _exotic_. In this latter case
-caution must be used in making determinations. Many minerals are
-primarily colorless, but take on exotic colors as a result of the
-presence of small quantities of impurities; for instance, pure corundum
-is colorless, but with a trace of iron oxide present becomes red, and is
-called the ruby, or with a trace of cobalt becomes blue and is called
-sapphire.
-
-
-
-
-                              CHAPTER III
-                              THE MINERALS
-
-
-          KEY TO THE MINERALS, BASED ON HARDNESS, COLOR, ETC.
-
-                                  OPAQUE COLORS
-    Color      Hardness     Streak            Remarks             Mineral
-
- Red
-    scarlet    2.5      scarlet         surface tarnishes   prousite
-                                        black
-               2.5      vermilion       surface scarlet to  cinnabar
-                                        dark red
-    ochre      7        white           non-crystalline     jasper
-               6        ochre red       color red to        hematite
-                                        almost black
-    rose       4        white           effervesces in      rhodochrosite
-                                        warm acid
-    dark       4        orange                              zincite
-               2.5      purplish red    surface tarnishes   pyrargyrite
-                                        black
-    brownish   3.5      brownish red                        cuprite
- Orange        3.5      white to                            pyromorphite
-                        yellowish
-               1-1½     orange                              realgar
- Blue          5.5-6    white           in igneous rocks    sodalite
-    azure      4        azure                               azurite
-    sky        7 & 4.5  white           blade-like crystals cyanite
-    turquoise  6        blue            non-crystalline     turquois
-               2-4      white                               chrysocolla
- Green
-    malachite  3.5      lighter green                       malachite
-    olive      6.5-7    white           in igneous rocks    olivine
-               3.5      white to yellow                     pyromorphite
-               2        white           mica-like cleavage  chlorite
-               1        white           greasy feel, color  talc
-                                        light to dark
-                                        olive green
-    yellowish  6.5      white                               epidote
-               2.5-4    white           color yellow green  serpentine
-                                        to olive
- Yellow
-    golden     2.5      shining         non-crystalline     gold
-    brassy     6        greenish-black  usually crystalline pyrite
-               6        greenish-gray   color pale brassy   marcasite
-                                        yellow, usually
-                                        non-crystalline
-               5.5      greenish-black  colors nitric acid  millerite
-                                        green
-               4        greenish-black  color golden        chalcopyrite
-                                        similar to gold
-               3.5      dark brown      purplish tarnish    tetrahedrite
-                                        on surface
-    bronze     5.5      pale            color with coppery  niccolite
-                        brownish-black  cast
-               4        dark gray-black with speedy black   pyrrhotite
-                                        tarnish
-               3        gray-black      brownish with       bornite
-                                        bluish tarnish
-               2.5      shining         coppery red color   copper
-    sulphur    3.5      white to        compact masses      pyromorphite
-                        yellowish
-               2        yellow                              sulphur
-               1-3                      earthy masses       carnotite
- Brown
-    violet     1½       shining         tarnishes black     cerargyrite
-    yellowish  7.5      white           4-sided prisms      zircon
-               6.5      gray                                cassiterite
-               5.5      ochre yellow    compact to earthy   limonite
-                                        masses
-               5        brownish-yellow                     goethite
-               4.5      black                               wolframite
-               3.5      yellowish-brown                     sphalerite
-               3.5      white                               siderite
-    grayish    7.5      white           often twinned       staurolite
-               6.5      pale brown                          rutile
-               3.5      white to        earthy masses       pyromorphite
-                        yellowish
-    reddish    7        white           dodecahedrons &     garnet
-                                        trapezohedrons
- Black         6.5      gray                                cassiterite
-               6        reddish-brown                       franklinite
-               6        black           magnetic            magnetite
-               5.5      dark brown                          chromite
-               5.5      black           yellow precipitate  wolframite
-                                        in sulphuric acid
-               5-6      black           non-magnetic        ilmenite
-               5-6      brownish-black  compact masses      psilomelane
-               5        brownish-yellow surface often       goethite
-                                        brownish
-               3.5      dark brown      tetrahedrons        tetrahedrite
-               2.5      silvery         fresh surfaces      silver
-                                        silver color
-               2.5      scarlet         fresh surfaces      prousite
-                                        bright red
-               2.5      purplish red    fresh surfaces red  pyrargyrite
-               2        black           earthy masses       pyrolusite
-               1        steel gray      greasy feel         graphite
- Metallic      2.5      black           tarnishes black,    chalcocite
-   Gray                                 bluish, or green
-               2.5      lead gray       sectile             argentite
-               2.5      lead gray       cubic cleavage      galena
-               2        lead gray       long prismatic      stibnite
-                                        crystals
-               1.5      bluish gray     in scales           molybdenite
-    steel      5.5      gray black      rose color in       smaltite
-                                        nitric acid
-               4.5      steel gray      very heavy          platinum
-               4        reddish black   often in striated   manganite
-                                        prisms
-               1        gray            with greasy feel    graphite
-    silvery    5.5      black                               arsenopyrite
-               2.5      silvery         tarnishes black on  silver
-                                        exposure
-    reddish    5.5      gray black      rose color in       cobaltite
-                                        nitric acid
-    pearly     1-1½     shining         exposed surfaces    cerargyrite
-                                        violet brown
- White, with   4        white           porcelainous        magnesite
-   impurities                           masses,
-                                        effervesces in acid
-    grayish    2        white           earthy masses,      kaolinite
-   or                                   greasy feel
-   yellowish
-               1-3      white           earthy masses       bauxite
-               1        white           greasy feel,        talc
-                                        fibrous or scaly
-
-                    TRANSPARENT OR TRANSLUCENT COLORS
-   Color   Hardness                 Remarks                   Mineral
-
-  Colorless or with faint tinges of color due to impurities
-           10       in octahedrons                          diamond
-           9        in hexagonal prisms                     corundum
-           8        in hexagonal prisms                     topaz
-           7        in three-sided prisms                   tourmaline
-           7        in hexagonal prisms                     quartz
-           7        non-crystalline                         chalcedony
-           7 or 4.5 cubes with beveled edges                boracite
-           6        non-crystalline, pearly luster          opal
-           5.5      rhombohedrons                           willemite
-           5.5      trapezohedrons                          analcite
-           5.5      tufts of needle-like crystals           natrolite
-           5.5      sheaf-like bundles of crystals          stilbite
-           5        hexagonal prisms with basal cleavage    apatite
-           5        effervesces in acid                     smithsonite
-           5        becomes jelly-like in acid              calamine
-           4.5      monoclinic prisms                       colemanite
-           4        in cubes                                fluorite
-           3.5      effervesces in acid, but one cleavage   aragonite
-           3.5      effervesces in acid, heavy              cerrusite
-           3        effervesces in acid, rhomboidal         calcite
-                      cleavage
-           3        no effervescence, but soluble in        anglesite
-                      nitric acid
-           2.5      in cubes tastes of salt                 halite
-           2        soluble in water, sweetish taste        borax
-           2        1 perfect cleavage, and two imperfect   gypsum
-                      cleaves at 66 with each other
-  White or with faint tinges of color due to impurities, such as pink,
-     bluish, etc.
-           7        hexagonal prisms                        quartz
-           7        non-crystalline                         chalcedony
-           7 or 4.5 cubes with beveled edges                boracite
-           6        non-crystalline, pearly luster          opal
-           6        cleavage in 3 directions, good in 2     feldspar
-                      and imperfect in the other
-           5.5      short eight-sided prisms                pyroxene
-           5.5      long six-sided prisms                   amphibole
-           5.5      trapezohedrons                          analcite
-           5.5      tufts of needle-like crystals           natrolite
-           5.5      sheaf-like bundles of crystals          stilbite
-           5.5      rhombohedrons                           willemite
-           5        effervesces in acid                     smithsonite
-           5        becomes jelly-like in acid              calamine
-           4.5 & 7  cubes with beveled edges                boracite
-           4.5      monoclinic prisms                       colemanite
-           4        effervesces in acid, porcelainous       magnesite
-           3.5-4    effervesces in acid, heavy, red color   strontianite
-                      in flame
-           3.5      effervesces in acid, heavy, green       witherite
-                      color in flame
-           3.5      effervesces in warm acid, rhomboidal    dolomite
-                      cleavage
-           3.5      effervesces in acid, cleavage in one    aragonite
-                      direction only
-           3.5      effervesces in acid, heavy, does not    cerrusite
-                      color flame
-           3-3.5    no effervescence, cleavage in three     anhydrite
-                      directions at right angles
-           3        effervesces in acid, rhomboidal         calcite
-                      cleavage
-           3        tabular crystals, heavy, green color    barite
-                      in flame
-           2-3      cleaves in thin elastic sheets          mica
-           2.5      cleaves in cubes                        cryolite
-           2.5      cubes, soluble in water, salty taste    halite
-           2        1 perfect cleavage, and 2 less perfect  gypsum
-                      ones
-           2        cleaves in thin non-elastic sheets      chlorite
-           2        soluble in water, tastes sweet          borax
-           1        greasy feel                             talc
-  Green    9        hexagonal prisms                        oriental
-                                                            emerald
-           8        octahedrons                             spinel
-           7.5      hexagonal prisms                        beryl
-           7        three-sided prisms                      tourmaline
-           7        dodecahedrons or trapezohedrons         garnet
-           7        non-crystalline                         prase or
-                                                            plasma
-           6.5-7    non-crystalline, olive color            olivine
-           6.5      yellow green color, rather opaque       epidote
-           6        non-crystalline, pearly luster          opal
-           5.5      short eight-sided prisms                pyroxene
-           5.5      long six-sided prisms                   amphibole
-           5        hexagonal prisms                        apatite
-           4        cubes                                   fluorite
-           3.5      effervesces in acid                     cerrusite
-           2.5-4    somewhat greasy feel, massive or        serpentine
-                      fibrous
-           2        in mica-like scales, non-elastic        chlorite
-           1        greasy feel, fibrous or scaly           talc
-  Red      9        hexagonal prisms                        ruby
-           8        octahedrons                             spinel
-           7        three-sided prisms                      tourmaline
-           7        dodecahedrons or trapezohedrons         garnet
-           7        hexagonal                               rose quartz
-           7        non-crystalline                         jasper or
-                                                            carnelian
-           6        pearly luster                           fire opal
-           4        cubes, rose tints                       fluorite
-           2-3      pink mica-like scales                   lepidolite
-  Blue     9        hexagonal prisms                        sapphire
-           7 & 4.5  blade-like crystals                     cyanite
-           6        non-crystalline masses                  turquois
-           5.5-6    in igneous rocks                        sodalite
-           4        azure color                             azurite
-           3.5      effervesces in acid, heavy              cerrusite
-           2-4      earthy masses, turquoise color          chrysocolla
-  Violet   7        hexagonal prisms                        amethyst
-           4        cubes                                   fluorite
-  Yellow   9        hexagonal prisms                        oriental
-                                                            topaz
-           8        octahedrons                             spinel
-           8        hexagonal prisms                        topaz
-           4        cubes                                   fluorite
-  Brown    9        hexagonal prisms                        corundum
-           8        octahedrons                             spinel
-           7.5      four-sided prisms                       zircon
-           7        hexagonal prisms                        smoky quartz
-           7        three-sided prisms                      tourmaline
-           7        non-crystalline                         flint
-           6        non-crystalline                         opal
-           5.5      short eight-sided prisms                pyroxene
-           5.5      long six-sided prisms                   amphibole
-           2-3      cleaves into thin sheets                mica
-  Black    9        hexagonal prisms                        corundum
-           8        octahedrons                             spinel
-           7        three-sided prisms                      tourmaline
-           5.5      short eight-sided prisms                pyroxene
-           5.5      long six-sided prisms                   amphibole
-           2-3      cleaves in thin sheets                  mica
-
-
-                             The Gold Group
-
-Gold was undoubtedly the first metal to be used by primitive man; for,
-occurring as it did in the stream beds, its bright color quickly
-attracted the eye, and it was so soft, that it was easily worked into
-various shapes, which, because they did not tarnish, became permanent
-ornaments. The metal is associated with the very earliest civilizations,
-being found in such ancient tombs as those at Kertsch in Crimea and in
-northern Africa and Asia Minor. It was used in the cloisonné work of
-Egypt 3000 years B.C. In America the Indians, especially to the south,
-were using it long before the continent was discovered.
-
-Of all the metals gold is the most malleable, and its ductility is
-remarkable, for a piece of a grain’s weight (less than the size of a pin
-head) can be drawn out into a wire 500 feet long; and it can be beaten
-into a thin leaf as thin as ¹/₂₅₀₀₀₀ of an inch in thickness, and thus a
-bit, weighing only a grain, can thus be spread over 56 square inches.
-
-It forms very few compounds, but has a considerable tendency to make
-alloys (_i.e._, mixtures with other metals without the resulting
-compound losing its metallic character). In Nature gold is never
-entirely pure, but is an alloy, usually with silver, there being from a
-fraction of 1% up to 30% of the silver with the gold, the more silver in
-the alloy, the paler the color of the gold. Australian gold is the
-purest, having but about .3% of silver in it, while Californian gold has
-around 10% and Hungarian gold runs as high as 30% of silver. Another
-alloy fairly abundant in Nature is that with tellurium, such as
-_calaverite_ (AuTe₂) which is a pale brassy yellow, similar to pyrite,
-but with the hardness of but 2.5. Another combination includes gold,
-silver and tellurium, _sylvanite_, (AuAgTe₄) a silvery white mineral
-with a hardness of but 2. Such combinations are known as tellurides and
-the calaverite is mined as a source of gold at Cripple Creek, Colo.,
-while the sylvanite is one of the important ores of gold in South
-Africa. Occasionally gold is also found alloyed with platinum, copper,
-iron, etc. Jewelers make several alloys, “red gold” being 3 parts gold
-and 1 of copper, “green gold” being the same proportions of gold and
-silver, and “blue gold” being the combination of gold and iron. Our gold
-coins are alloys, nine parts gold and one of copper, to give them
-greater durability. Most of the gold recovered from nature is found
-native, _i.e._, the pure metal, or with some alloy.
-
-
-Gold
-Au
-Pl. 5
-
-Usually non-crystalline, but occasionally showing cube or octahedral
-faces of the isometric system; hardness 2.5; specific gravity 19.3;
-color golden yellow; luster metallic; opaque.
-
-Gold is mostly found as the metal and is readily recognized by its
-color, considerable weight, hardness, malleability, and the fact that it
-does not tarnish. It usually occurs in quartz veins in fine to thick
-threads, scales or grains, and occasionally in larger masses termed
-“nuggets.” It is insoluble in most liquids so that when weathered from
-its original sites, it was often washed down into stream beds, to be
-found later in the sands or gravels, or even in the sea beaches. When
-thus found it is termed “placer gold,” and its recovery is placer
-mining. Most of the original discoveries of gold have been in these
-placer deposits; and from them it has been traced back to the ledges
-from which it originally weathered. In the placer deposits the size of
-the particles varies from fine “dust” up to large nuggets, the largest
-found in California weighing 161 pounds; but the largest one found in
-the world was the “Welcome Nugget,” found in Australia, and weighing 248
-pounds. When gold was discovered in California in 1848, this became the
-chief source for the world, but later this distinction went to
-Australia, and now belongs to South Africa, which today yields over half
-the annual supply.
-
-The ultimate source of gold is from the lighter colored igneous rocks,
-like granites, syenites, and diorites, throughout which it is diffused
-in quantities too small to be either visible or worth while to extract.
-It becomes available only when it has been dissolved out by percolating
-waters and segregated in fissures or veins, either in or leading from
-these igneous rocks. Generally this transfer of gold has taken place
-when the rocks were at high temperatures, and by the aid of water (and
-perhaps other solvents) which was also at high temperatures. The
-presence of gold in sandstones, limestones, etc., is secondary, as is
-also its presence in sea water, in which there is reported to be nearly
-a grain (about five cents worth) in every ton of water. Beside the
-direct recovery of gold from gold mining, a great deal is obtained from
-its association with iron, copper, silver, lead and zinc sulphides, in
-which it is included in particles too fine to be visible, but in
-quantities large enough to be separated from the other metals after they
-are smelted.
-
-In the United States gold is found in the Cordilleran region from
-California to Alaska, in Colorado, Nevada, Arizona, Utah, the Black
-Hills of South Dakota, and in small quantities in the metamorphosed
-slates of North and South Carolina, Georgia, and in Nova Scotia.
-
-
-                            The Silver Group
-
-Though much commoner than gold, silver did not attract the eye of man as
-early, probably because it tarnishes when exposed to air or any other
-agent having sulphur compounds in it, and a black film of silver
-sulphide covers the surface. Its first use was for ornaments, and some
-of these found in the ruins of ancient Troy indicate its use as early as
-2500 B.C. A thousand years later it was being used to make basins, vases
-and other vessels.
-
-Silver is next to gold in malleability and ductility, so that a grain of
-silver can be drawn out into a wire 400 feet long, or beaten into leaves
-¹/₁₀₀₀₀₀ of an inch in thickness. As a conductor of electricity it is
-unsurpassed, being rated at 100% while copper rates 93%. Silver is also
-like gold in the freedom with which it alloys with other metals, such as
-gold, copper, iron, platinum, etc. All our silver coins, tableware,
-etc., have some copper alloyed with the silver to give it greater
-hardness and durability.
-
-Unlike gold, silver freely enters into compounds with the non-metals,
-which is the reason that it is not found primarily in its native state,
-but usually as a sulphide. Its ultimate source is in the igneous rocks,
-few granites or lavas, on analysis, failing to show at least traces of
-silver. Before it is available as an ore, or mineral, it has been
-dissolved from the original magma, and segregated in fissures or veins,
-along with such minerals, as quartz, fluorite, calcite, etc. This seems
-to have taken place while the igneous rocks were still hot, and by the
-agency of vapors and liquids which were also hot. The presence of silver
-in sedimentary and metamorphic rocks, or even in sea water, is
-secondary.
-
-The primary deposition of silver is usually in the form of sulphides,
-the commoner of which are, argentite or silver sulphide, pyrargyrite or
-silver and antimony sulphide, and prousite, or silver and arsenic
-sulphide. Its occurrence as native silver, or the chloride, cerargyrite,
-is secondary and due to the reactions which have taken place when
-sulphide deposits have been subjected to weathering agents.
-
-The United States produces about 25% of the world’s supply, Mexico some
-35%. It is especially found along the Cordilleran ranges of both North
-and South America.
-
-
-Silver
-Ag
-Pl. 6
-
-Usually non-crystalline, but occasionally showing cube or octahedron
-faces of the isometric system; hardness 2.5; specific gravity 10.5;
-color silvery white; luster metallic; opaque.
-
-When found in its native state silver is usually in wirey, flakey, or
-mossy masses; but sometimes masses of considerable size occur, the most
-famous being an 800 pound nugget found in Peru, and another of 500
-pounds weight found at Konsberg, Norway, and now preserved in
-Copenhagen. When exposed to the air the surface soon tarnishes and takes
-on a black color which must be scraped off to see the real color.
-
-Like gold, silver is usually found associated with other metals, like
-iron, copper, lead and zinc; and much of the silver recovered is
-obtained in connection with the mining, especially of copper and lead.
-Some lead ores have so much silver in them that they are better worth
-mining for the silver; galena, for instance, under such circumstances
-being termed argentiferous galena. Native silver is a secondary mineral,
-having been formed by the reduction of some one of its sulphides by
-water, carrying various elements which had a greater affinity for the
-sulphur.
-
-Silver is found along with copper in the Lake Superior region, and in
-Idaho, Nevada, and California.
-
-
-Argentite
-AgS
-Pl. 6
-_silver glance_
-
-Usually in irregular masses, but sometimes in cubes; hardness 2.5;
-specific gravity 7.3; color and streak lead gray; luster metallic;
-opaque on thin edges.
-
-Argentite, the simple sulphide of silver, is the chief source from which
-silver is obtained. It looks like galena, and has the same hardness,
-streak and specific gravity, but can be distinguished by the galena
-having a very perfect cubic cleavage while the argentite has no
-cleavage. Argentite is easily cut with a knife (sectile). It is usually
-found in irregular masses, but sometimes in cubes which make very choice
-cabinet specimens; and is associated with such other minerals as galena,
-sphalerite, chalcopyrite, pyrite, fluorite, quartz, and calcite.
-
-It occurs in fissures and veins all through the Cordilleran regions,
-especially in California, Colorado, Nevada (Comstock Lode), Arizona
-(Silver King Mine) and about the shores of Lake Superior.
-
-
-Pyrargyrite
-Ag₃SbS₃
-Pl. 7
-_ruby silver_ or _dark red silver_
-
-Usually occurs in irregular masses; hardness 2.5; specific gravity 5.8;
-color dark red to black; streak purplish red; luster metallic to
-adamantine; translucent on thin edges.
-
-Pyrargyrite, the sulphide of silver and antimony, is distinguished by
-its dark red color and the purplish streak. It may look like prousite,
-but is easily distinguished from the latter which has a scarlet streak.
-It also at times looks like hematite and cinnabar, but the hematite has
-a hardness of 6, and the latter has the bright red color throughout,
-while pyrargyrite turns black when exposed to the light, so that the
-characteristic red color will be seen only on fresh surfaces. The
-characteristic red color can only be kept on the mineral if it is
-constantly protected from the light.
-
-Sometimes pyrargyrite occurs in crystals and these belong to the
-hexagonal system, and are prisms with low faces on the ends, as on plate
-7, and the mineral is peculiar in that the faces on the opposite ends
-are unlike.
-
-Pyrargyrite is found mostly in fissures and veins of quartz, fluorite,
-calcite, etc., and associated with pyrite, chalcopyrite, galena, etc. It
-is fairly common in Colorado in Gunnison and Ouray counties, in Nevada,
-New Mexico, Arizona, etc.
-
-
-Prousite
-Ag₃ AsS₃
-Pl. 7
-_light red_
-_silver_
-
-Usually occurs in irregular masses; hardness 2.5; specific gravity 5.6;
-color scarlet to vermilion; streak the same; luster adamantine;
-transparent on thin edges.
-
-In general this mineral is very like pyrargyrite, but has the scarlet
-color and streak which are entirely characteristic. It is likely to have
-the surface tarnished black, which happens on exposure to light, so that
-it is essential to be sure that fresh surfaces are being examined.
-Occasionally it is found in crystals, of the same type as the preceding
-mineral. It is generally found associated with pyrargyrite.
-
-
-Cerargyrite
-AgCl
-_horn silver_
-
-Usually found in irregular masses or incrustations; hardness 1 to 1½;
-specific gravity 5.5; color pearly gray, grayish green to colorless, but
-turning violet brown on exposure to light; luster resinous; transparent
-on thin edges.
-
-This mineral is usually found in thin seams or waxy incrustations, but
-it may occur in crystals in which case they are cubes. It is very soft
-and easily cut with a knife, which with its tendency to turn
-violet-brown on exposure to light, makes it easy to identify.
-Cerargyrite is a secondary mineral, resulting from the action of
-chlorine-bearing water on some one of the sulphides of silver. It is
-found in the upper portions of mines, especially those in arid regions.
-
-
-                            The Copper Group
-
-After gold the next metal to be utilized was copper. About 4000 B.C. our
-early forefathers found that by heating certain rocks, they obtained a
-metal which could be pounded, ground and carved into useful shapes.
-Curiously enough the rocks which had the copper also had some tin in
-them, so that this first-found copper was not pure, but had from five to
-ten per cent of tin in it, making the resulting metal harder, and what
-we call bronze. It was some thousands of years later before they
-distinguished the copper as a pure metal, but it worked and made good
-tools. The newly found metal was not as ornamental as gold; but, because
-it could be made into tools, it had a tremendous influence on man’s
-development. As the bronze tools began to take the place of the stone
-implements, the “Age of Bronze” was ushered in. In America the Indians
-in the Lake Superior region found native copper weathered out of the
-rocks and later mined it, and they too pounded it into knives, axes,
-needles, and ornaments, but probably never learned to melt it and mold
-their tools. At any rate they were not as far advanced in using this
-metal when Columbus landed as were the southern Europeans 6500 years
-earlier. Since the use of iron became general, copper has not held such
-a dominant place, but it still is “the red metal” which holds the second
-most important place.
-
-It is malleable and ductile, though not equal to gold or silver in these
-respects. It is a good conductor of electricity and a very large amount
-of copper is used in electrical manufacture, roofing, wire, etc. It
-alloys with other metals; ten parts copper and one of tin being bronze,
-ten of copper and one of zinc is brass, and copper with aluminum is
-aluminum bronze.
-
-Like silver and gold, copper is widely diffused through the igneous
-rocks, but before it is available, it must be leached out by solvents
-and concentrated in veins, fissures, or definite parts of the lavas or
-granites. The primary ores are those which, while the igneous rock was
-still hot, were carried by hot vapors and liquids into the fissures and
-there deposited, mostly as sulphides. There is a long list of these, but
-in this country, the following are the commoner ones; chalcocite the
-sulphide of copper, chalcopyrite the sulphide of copper and iron,
-bornite another combination of copper, iron and sulphur, and
-tetrahedrite copper and antimony sulphide. When these primary ores are
-near enough to the surface to come in contact with waters carrying
-oxygen, carbon dioxide or silica in solution, they may give up their
-sulphur and take some one of these new elements and we have such forms
-as cuprite, the oxide of copper, malachite and azurite, carbonates of
-copper, or chrysocolla, the silicate of copper. Native copper is also a
-secondary deposit laid down in its present state by a combination of
-circumstances which deprived it of its original sulphur. In general
-copper mining can not be profitably carried on for ores with anything
-less than a half of one percent in them; and the use of such low grade
-ores has only been possible for a few years, as the result of inventing
-most delicate processes in the smelting.
-
-The United States produces about a quarter of the world’s supply of
-copper, with Chile ranking second with about 17%.
-
-
-Copper
-Cu
-Pl. 8
-
-Usually in irregular masses; hardness 2.5; specific gravity 8.9; color
-copper red; luster metallic; opaque. Native copper, easily determined by
-its color and hardness, is generally found in irregular grains, sheets,
-or masses, on which may sometimes be detected traces of a cube or an
-octahedral face, showing that it belongs to the isometric system. The
-most famous locality is the Upper Peninsula of Michigan which may be
-taken as typical. Here, long before it was known historically, the
-Indians found and dug out copper to make knives, awls, and ornaments.
-
-In this region, beds of lava alternate with sandstones and
-conglomerates. The copper was originally in the lavas, but has been
-dissolved out, and now fills cracks and gas cavities in the lavas, and
-also the spaces between the pebbles of the conglomerate. This locality
-has been very famous both because of the quantity mined, and also
-because of the strikingly large masses sometimes found. Today but little
-of the ore runs above 2 percent copper, and it is mined if it has as
-little as ½ of one percent.
-
-While nowhere near as abundant, native copper occurs in the same way in
-cavities and cracks in the trap rocks of New Jersey, and along the south
-shore of the Bay of Fundy. It is also known from Oregon, the White River
-region of Alaska, and in Arctic Canada.
-
-
-Chalcopyrite
-CuFeS₂
-Pl. 8
-_copper pyrites_ or _yellow copper ore_
-
-Occurs in crystals of irregular masses; hardness 4; specific gravity
-4.2; color bronze yellow; streak greenish black; luster metallic; opaque
-on thin edges.
-
-Chalcopyrite resembles pyrite, but its color is a more golden yellow,
-and its surface tarnishes with iridescent colors. Then too the hardness
-of chalcopyrite is but 4 as compared with 6 for pyrite. When in crystals
-this mineral belongs to the tetrahedral system as the c axis is but .985
-in length as compared with I for the two other axes. This difference is
-so little that, to the eye, the octahedron appears to belong to the
-isometric system. Chalcopyrite occurs in octahedrons and tetrahedrons
-(as on plate 8), the latter being the form where but half of the
-octahedral faces are developed. However by far the most frequent mode of
-occurrence is in irregular masses.
-
-This is the most important primary ore of copper, and is widely
-distributed, being found either in lavas, or in veins, or in fissures
-connected with igneous rocks. Apparently the deposits were made, either
-at the time of eruptive disturbances or shortly afterward, from vapors
-or hot solutions carrying the copper sulphides (and other sulphides)
-from the molten igneous rocks. Chalcopyrite is usually associated with
-pyrite, galena, sphalerite and chalcocite, as well as quartz, fluorite
-and calcite. It is found in all the New England States, in New York, New
-Jersey, Pennsylvania, Maryland, Virginia, North Carolina, Tennessee,
-Missouri, and all the Rocky Mountain and Pacific Coast States.
-
-
-Bornite
-Cu₃FeS₃
-_purple copper ore_
-
-Occurs in granular or compact masses; hardness 3; specific gravity, 5;
-color bronze-brown with a bluish tarnish; streak gray-black; luster
-metallic; opaque on thin edges.
-
-Bornite is also known as erubescite, blushing ore, variegated copper,
-peacock copper, etc., all of which names refer to the highly iridescent
-tarnish which fresh faces soon take on when exposed to the air. Though
-usually in masses, it is sometimes found in rough cubes of the isometric
-system. In this country it is not abundant enough to be used as an ore,
-but is likely to be found with other ores like chalcopyrite or
-chalcocite. In the east it has been found at Bristol, Conn., and near
-Wilkesbarre, Penn., while in the west it may be expected to occur
-wherever other sulphide minerals of copper are found.
-
-
-Chalcocite
-Cu₂S
-Pl. 9
-_copper glance_
-
-Occurs in fine grained compact masses; hardness 2.5; specific gravity
-5.7; color dark leaden gray; streak black; luster metallic; opaque on
-thin edges.
-
-Chalcocite is one of the important ores of copper, especially in Arizona
-and the Butte District of Montana. It resembles argentite in color and
-general appearance, but is readily distinguished by being brittle and
-having a tendency to tarnish to bluish or greenish colors on fresh
-surfaces. Occasionally it occurs in crystals which are in the
-orthorhombic system; but the edges of the prism are so beveled that
-there are six sides and the prism resembles a hexagonal prism (see page
-16).
-
-In the Butte, Mont., district, the most important copper region in the
-United States, fully 50% of the ore is chalcocite, which is a derivative
-of the originally deposited chalcopyrite, the latter having lost its
-iron. In the veins of this district chalcopyrite, bournite,
-tetrahedrite, and several other copper minerals not described in this
-book, occur all together, and with them also gold, silver and arsenic
-minerals. The gold amounts to about 2¼ cents per pound of copper, and
-the silver is in somewhat less quantity. These veins were first opened
-to get the silver ores, which were the more important ones down to a
-depth of 200 to 400 feet. Below these depths the copper became much more
-important. It was the weathering which had removed a large part of the
-copper minerals in the upper levels of the veins, but had left a large
-part of the silver. Chalcocite is also important in most of the Utah and
-Arizona mines.
-
-In the east it has been found at Bristol, Simsbury and Cheshire, Conn.,
-and in the west it is found in all the Cordilleran States.
-
-
-Tetrahedrite
-Cu₃SbS₃
-Pl. 9 & 10
-_gray copper ore_
-
-Occurs in irregular masses and in tetrahedrons of the isometric system;
-hardness 3.5; specific gravity 4.7; streak dark brown; luster metallic;
-opaque on thin edges.
-
-In its crystalline form the tetrahedrite occurs in tetrahedrons, which
-generally have faces formed by beveling the edges and by cutting the
-corners, as in the two figures of plate 10. Chalcopyrite may also occur
-in tetrahedrons, but its golden yellow color is entirely different from
-the gray-black of the tetrahedrite. When in masses the hardness and the
-streak which is dark brown, are very characteristic.
-
-In England and Bolivia tetrahedrite is an important ore of copper, but
-in this country it is simply a copper mineral which is widely
-distributed, and associated with most of the mining enterprises, but is
-in no case the important ore. It has been found sparingly through the
-New England States, at the Kellogg Mines in Arkansas, and abundantly in
-Colorado, Montana, Utah, Arizona, Nevada and New Mexico.
-
-
-Cuprite
-Cu₂O
-Pl. 9 & 10
-_red copper ore_
-
-Occurs in isometric cubes, octahedrons, and dodecahedrons, or in masses;
-hardness 3.5; specific gravity 6; color dark brownish-red; streak
-brownish-red; luster metallic; translucent on thin edges.
-
-When in crystals cuprite is easily determined, but when in masses its
-fresh surfaces may suggest prousite, but the streak and hardness are
-quite different in the two cases. Sometimes its color suggests hematite,
-but the latter has the hardness of 6. When found it is often coated with
-a thin film of green, which is malachite.
-
-Except when found as native copper, the ore which contains the greatest
-percentage of copper is cuprite with 88.8% of copper. It is likely to
-occur in any of the deposits of copper ore, where they are in arid
-climates and above the level of the underground water, and is very
-frequently associated with malachite and azurite. In the Bisbee,
-Arizona, district cuprite is one of the important ores.
-
-Besides the normal occurrence described above, cuprite may be found in
-two other varieties; one where the crystals have grown side by side and
-so only the ends have been free for continuous additions of the mineral,
-which has resulted in a fibrous mass known as “plush copper ore” or
-chalcotrichite; the other an earthy mixture of limonite and cuprite,
-which is brick red in color, and termed “tile ore.”
-
-Cuprite is found sparingly in New England, more abundantly at such
-places as Summerville and Flemington, N. J., Cornwall, Penn., in the
-Lake Superior region, and fairly abundantly in the Cordilleran States.
-
-
-Malachite
-CuCO₃·Cu(OH)₂
-Pl. 11
-
-Usually occurs in nodular or incrusting masses; hardness 3.5; specific
-gravity 4; color green; streak a lighter green; luster adamantine, silky
-or dull; translucent on thin edges.
-
-The vivid green of malachite is usually enough to determine it at once,
-but one may be sure by trying a drop of acid on it, in which case it
-effervesces as is characteristic of so many carbonates, but this is the
-only carbonate which is vivid green. Generally the malachite is in
-irregular masses, but crystals are occasionally found. These are
-extremely small and needle-like, and belong to the monoclinic system. In
-the Ural Mountains there is a locality where these crystals grow in
-fibrous masses, usually radiating from the center. Malachite in such
-nodules has a silky luster. These rare nodules have furnished the rulers
-of Russia with a unique and much prized material for making royal gifts.
-In European museums and palaces one finds many objects carved from this
-form of malachite, and marked as gifts of the czars of Russia.
-
-In the United States malachite is widely distributed, appearing as green
-streaks and stains where copper minerals have been exposed to the air.
-It is the green tarnish which appears on bronze and copper when exposed
-to the weather. It is found in large quantities in New Jersey,
-Pennsylvania, Wisconsin, Nevada, Arizona, Utah, New Mexico, etc. The
-Bisbee mine in Arizona is the place that has furnished museums with so
-many of the handsome specimens of malachite associated with azurite.
-These are the most striking specimens for the vividness of their colors
-that appear in any collections.
-
-Malachite has been known since about 4000 B.C., the Egyptians having
-mines where they obtained it between the Suez and Mt. Sinai. In those
-early days it was particularly a child’s charm, protecting the wearer
-from evil spirits. It is still used as a stone of lesser value in making
-some sorts of jewelry.
-
-
-Azurite
-2CuCO₃·Cu(OH)₂
-Pl. 11
-
-Occurs as short prismatic or tabular crystals of the monoclinic system;
-hardness 4; specific gravity 3.8; color azure blue; streak lighter blue;
-luster vitreous; translucent on thin edges.
-
-Azurite is another very striking mineral fully characterized by its
-color and streak. Like malachite it effervesces in acid. It is very near
-to malachite in composition, and by increasing its water content, can
-and freely does change to the green mineral; so that few specimens of
-azurite are without traces of malachite. It is found in the same places
-as malachite, but is not as abundant in the east.
-
-Azurite with the accompanying malachite is cut and polished to make
-semi-precious stones for some forms of jewelry.
-
-
-Chrysocolla
-CuSiO₃·2H₂O
-
-Never occurs in crystals, but in seams and incrustations; hardness 2-4;
-specific gravity 2.1; color bluish-green; streak white; luster vitreous;
-translucent on thin edges.
-
-This rather rare mineral often appears in opal- or enamel-like
-incrustations, and its color is variable ranging from the typical
-bluish-green to sky-blue or even turquoise blue. This is a mineral
-resulting from the action of silica bearing waters, coming in contact
-with most any of the copper minerals, and is found accompanying cuprite,
-malachite, azurite, etc. It is never in large enough quantities to be
-used as an ore, but its striking color attracts attention and it can be
-found fairly frequently, especially in the west.
-
-
-                             The Iron Group
-
-Pure iron is a chemical curiosity which looks very much like silver. As
-obtained from its ores, or as it occurs in Nature, iron always has some
-impurities with it, such as carbon, silicon, sulphur and phosphorus, and
-these are highest in the crudest iron such as “pig-iron.” Its
-malleability and ductility are only a little less than for gold and
-silver, and so it has a wide range of qualities for use by man. It is
-only rarely found native in minute grains in some of the dark lavas.
-There is however one remarkable exception to this statement, in that on
-Disco Island, Greenland, there is a basaltic rock, from which are
-weathered great boulders of native iron up to 20 tons in weight. This
-iron is very like that occurring in meteorites, and probably came from
-great depths in the earth’s interior. The specific gravity of iron is
-7.8. It makes up around 5% of the crust of the earth, and probably
-occurs in much larger percentages in the interior of the earth.
-
-Iron was discovered by man later than gold or silver or copper, about
-1000 B.C.; but once found it was so much more abundant than any of these
-that it soon dominated over copper, and from Roman times to the present
-has been the basis of progress in civilization, and these times are well
-called “the iron age.”
-
-Iron unites freely with the non-metals, and occurs as sulphides, oxides,
-carbonates, etc., and is also present as a secondary metal in that great
-group of minerals known as the silicates (see page 97). It alloys with a
-wide range of other metals, every combination altering the properties of
-the iron, and thus making it useful in a still greater range of
-manufacture. The introduction of ¼ to 2½% of carbon into iron makes
-steel, which is harder (in proportion to the amount of carbon) and
-stronger than the pure iron.
-
-Iron compounds are among the most numerous and important of the colors
-in Nature’s paint box, limonite furnishing the browns which color the
-soil and so many of the rocks, hematite giving the red color to other
-abundant rocks, and magnetite often coloring igneous rocks black, while
-the chlorophyll which gives the green color to plants is an iron
-compound, as is also the hemoglobin which gives the red to our blood.
-
-Iron is present in all igneous rocks, and secondarily in the sedimentary
-and metamorphic rocks. It is soluble in water, and so is being
-constantly transferred from place to place, and changes from one
-compound to another, according to the circumstances in which it is
-placed.
-
-The primary forms are pyrite, magnetite and the silicates. When in
-weathered rocks the iron is changed to limonite, siderite or hydrated
-silicates. Hematite is an intermediate oxide from which the water
-contained in limonite has been driven off by moderate heat or bacterial
-action.
-
-
-Limonite
-2Fe₂O₃·3H₂O
-Pl. 12
-
-Never crystalline, occurs in mammillary, botryoidal and stalactitic
-forms, or in fibrous, compact, oolitic, nodular or earthly masses;
-hardness 5.5; specific gravity 3.8; color yellow-brown to black; streak
-yellow-brown; luster metallic to dull; opaque.
-
-Limonite is a very common mineral, the color, streak and hardness
-identifying it readily. Iron rust is its most familiar form. When
-powdered it is the ochre yellow used in paints. Being so universally
-distributed, it is to be expected it will occur in a variety of ways.
-First, there is the fibrous type found lining cavities, in geodes, or
-hanging in stalactites in caves. This has a silky luster, an opalescent,
-glazed or black surface, and is in mammillated or botryoidal masses.
-Second, it may occur in compact masses in veins, where it was deposited
-by waters; which, circulating through the adjacent rocks, gathered it
-from the rocks, and, on reaching the open seams, gave it up again.
-Third, it may occur in beds on the bottom of ponds, where it was
-deposited by waters which gathered it as they flowed over the surface of
-the country rocks. Measurements in Sweden show that it may accumulate in
-such places as much as six inches in the course of twenty years. In
-ponds and swamps, the decaying vegetation forms organic compounds, which
-cause the precipitation of the iron from the water, as it is brought in
-by the streams. This sort of iron in the bottom of ponds or swamps is
-also known as “bog iron.” Another form in which limonite may occur in
-ponds, lakes, or even the sea, is in oolitic masses. In this case the
-iron forms in tiny balls, with perhaps a grain of sand at the center,
-and one coat of iron after another formed around it, like the layers of
-an onion. If the resulting balls are tiny this is called oolitic (like
-fish eggs), but if the balls are larger it is pisolitic (like peas).
-Bacteria probably have a good deal to do with the precipitation of
-limonite in this manner. Fourth, limonite occurs in earthy masses,
-usually mixed with impurities like clay and sand, which are the residue
-left behind, where limestones have been dissolved by weathering. The
-fifth mode of occurrence is known as gossan, or “the iron hat,” which is
-a mass of limonite capping a vein of some sulphide mineral, like pyrite,
-chalcopyrite or pyrrhotite, which has been exposed to weathering; and in
-these minerals the sulphur has been removed, leaving a mass of limonite
-over the vein. This is particularly common in the west. Limonite is
-quite easily fusible and so was probably the first ore from which early
-man extracted iron.
-
-Limonite is iron oxide, with 3 molecules of water of crystallization (or
-constitution) associated with every 2 molecules of the oxide. If
-limonite is moderately heated the water is driven out and the resulting
-compound is hematite, the same oxide, but without the water. In this
-case and many other similar cases, as gypsum, opal, etc., we have two or
-more minerals resulting from the presence or absence of water in the
-mineral. The water molecules have a definite place in the arrangement of
-molecules which determines the structure of the mineral. Sometimes the
-water is driven out at a temperature around 212 F., in which case it is
-called, water of crystallization, but in other cases as gypsum, a
-considerably higher temperature is required to drive out the water, and
-then it is called, water of constitution. In all cases the removal of
-the water changes the arrangement of molecules and a new mineral
-results, with characteristics of its own.
-
-In this case limonite is only one of a series of minerals which have the
-Fe₂O₃ molecule as a basis, and that incorporate more or less water into
-their molecular construction as follows:
-
-  Turgite               2Fe₂O₃·H₂O
-  Goethite              Fe₂O₃·H₂O
-  Limonite              2Fe₂O₃·3H₂O
-  Xanthosiderite        Fe₂O₃·2H₂O
-  Limonite              Fe₂O₃·3H₂O
-
-Of these goethite is crystalline, the others non-crystalline. They may
-occur pure or in all sorts of mixtures, the mixtures usually being
-lumped under limonite. The limonite is far the commonest of the series,
-goethite is fairly common, but the others are rare as pure minerals.
-
-Limonite is found in all parts of all states and in every country.
-Though so common, it is by no means an important source of iron today,
-only about one percent of the iron mined in this country coming from
-this source, though in Germany, Sweden and Scotland it is relatively
-much more important.
-
-
-Goethite
-Fe₂O₃·H₂O
-Pl. 12
-
-Occurs in lustrous brown to black orthorhombic prisms, usually
-terminated by low pyramids; hardness 5; specific gravity 4; color brown
-to black; streak brownish-yellow; luster imperfect adamantine; opaque.
-
-Goethite, named for the poet Goethe, who was interested in mineralogy,
-is much less abundant than limonite or hematite, but occurs with them,
-when they are in veins. Its usual form is an orthorhombic prism with the
-edges beveled, and a low pyramid on either end. The crystals usually
-grow in clusters, making a fibrous mass, often radiated, in which case
-it is known as “needle iron stone”; or the prisms may be so short as to
-be almost scales; when, because of the yellowish-red color, it is called
-“ruby mica”. It is found in many states, including Connecticut,
-Michigan, Colorado, etc.
-
-
-Hematite
-Fe₂O₃
-Pl. 13 & 14
-_specular iron_
-
-Occurs in compact, mammillary, botryoidal, or stalactitic masses of dark
-red to black color, or in earthy masses of bright to dark red; hardness
-6; specific gravity 5.2; color ochre red to black; streak cherry red to
-dark red; luster metallic, vitreous, or dull; opaque on thin edges.
-
-Hematite is readily distinguished from other red minerals by its
-hardness and streak. It may occur in crystals, which belong to the
-hexagonal system, and are usually hemihedral forms of the double
-pyramid, or rhombohedrons. These rhombohedrons usually have the edges
-beveled, as in Pl. 13, A; or are tabular in form as a result of the
-beveling of two of the opposite edges to such an extent that a form like
-Pl. 13 B results. However the usual occurrence is in non-crystalline
-masses, which represent transformations from limonite by the loss of
-water of crystallization on the part of the limonite. In such cases we
-have fibrous, oolitic or compact masses, according to the form in which
-the limonite occurred. The transformation from limonite into hematite
-involves some heat to drive out the water of crystallization, but
-nothing like what is involved in metamorphism.
-
-Hematite is the source of 90% of the iron mined in this country. Part of
-it comes from the famous Clinton iron ore, a layer a foot or more in
-thickness; starting in New York State, and extending all down the
-Appalachian Mountains to Alabama, where it is ten or more feet thick and
-the basis of the Birmingham iron industries. Then there are tremendous
-deposits of earthy to compact hematite, probably derived from limonite,
-around the west end of Lake Superior. This latter region yields today
-around 75% of the iron for this country.
-
-Loose earthy masses of hematite are often known as “ochre red,” and were
-used by the Indians for war paint. Today the same sort of material is
-obtained by powdering hematite and using it for red paint. The red color
-in great stretches of rock is due to the presence of small amounts of
-hematite, acting as cementing material. The red of the ruby, garnet,
-spinel, and the pink of feldspars and calcite are due to traces of
-hematite.
-
-This mineral is very common and found in every state.
-
-
-Magnetite
-Fe₃O₄
-Pl. 14
-_Magnetic iron ore_
-
-Occurs in masses or in isometric octahedrons or dodecahedrons; hardness
-6; specific gravity 5.8; color black; streak black; luster metallic;
-opaque on thin edges.
-
-Magnetite is another important ore of iron, and is peculiar in being
-strongly magnetic; its name being derived, according to Pliny, from that
-of the shepherd Magnes, who found his iron pointed staff attracted by
-the mineral when he was wandering on Mount Ida. This magnetic property
-has been repeatedly used to locate beds of magnetite, and is very
-helpful in separating magnetite from the “black sands,” of which it so
-often forms a part. These sands however generally have magnetite with so
-much titanium in it that they are unfit for smelting.
-
-Magnetite is found in association with igneous or metamorphic rocks, and
-often represents limonite or hematite which has been altered as the
-result of high temperatures. Some of it, in the igneous rocks
-especially, was undoubtedly in the molten magma and has crystallized out
-from the magma while it was still hot. It is the form of iron always
-indicative of former high temperatures. It is an ore mineral for about
-3% of the iron in this country, but in Scandinavia and some other
-countries, it plays a leading role as the source of iron.
-
-It is found in the Adirondack Mountains, in New Jersey, Pennsylvania,
-Arkansas, North Carolina, New Mexico, and California.
-
-
-Siderite
-FeCO₃
-Pl. 13 & 14
-_Spathic iron_
-
-Occurs in fibrous botryoidal masses or rhombohedral crystals, sometimes
-with curved faces; hardness 3.5; specific gravity 3.8; color gray-brown;
-streak white; luster vitreous; translucent on thin edges.
-
-Like hematite this mineral belongs to the hexagonal system, and
-crystallizes in hemihedral form, making the rhombohedron. Its faces are
-often curved, which is rare in minerals, only a few forms like this and
-dolomite having other than plane faces. When siderite crystals grow in
-clusters, the crowding often results in growth on one face only, making
-a mass of fibrous character, and in such cases the surface of the mass
-is botryoidal in contour. The mineral is likely to oxidize, losing its
-gray-brown color, and becoming limonite. In the United States it is
-scarcely ever used as an ore for iron, but in Germany and England a
-great deal of iron is smelted from this mineral.
-
-It occurs in Massachusetts, Connecticut, New York, throughout the
-Appalachian Mountains, and also in Ohio.
-
-
-Pyrite
-FeS₂
-Pl. 15 & 16
-_iron pyrites_
-
-Occurs as cubes, octahedrons and pyritohedrons, or in compact masses,
-scales or grains; hardness 6; specific gravity 5.1; color brassy yellow;
-streak greenish-black; luster metallic; opaque on thin edges.
-
-This is one of the commonest of all minerals. It is found in all kinds
-of rocks, with all kinds of associations, in all parts of the world. Its
-crystals are isometric, and cubes and octahedrons are abundant. The
-pyritohedron is also a common form, and characteristic of this mineral.
-It is a hemihedral form derived from a 24-sided form, _i.e._ the cube
-with four faces on each side. On this 24-sided form each alternate face
-has developed and the others have disappeared, resulting in a 12-sided
-form, known as the pyritohedron, which differs from the dodecahedron in
-that each of its faces is five-sided instead of rhomboidal. When in
-crystals pyrite can not be easily confused with any other mineral; but
-when in masses it is often mistaken for gold, chalcopyrite, pyrrhotite
-or marcasite. From the first two, the color should be sufficient to
-distinguish it, for they are golden yellow. Pyrrhotite is bronze yellow,
-and marcasite is paler yellow. Then too in hardness pyrite is much
-harder than any of these minerals except marcasite. This last is the one
-which is most likely to cause real difficulty. Its lighter color, and
-the fact that it usually comes in fibrous masses are the best
-distinctions.
-
-In spite of being so abundant pyrite is scarcely ever used as an ore for
-iron, because the sulphur makes the metal “short,” or brittle, and the
-sulphur is not easily gotten entirely out of the iron; but pyrite is
-used largely in the manufacture of sulphuric acid, so important to many
-of our industries.
-
-Other sulphides are commonly mixed with pyrite, such as chalcopyrite,
-arsenopyrite, argentite, etc.; but the most important impurity is gold,
-which is often scattered through the pyrite in invisible particles, and
-sometimes in quantities enough to make it worth while to smelt it for
-the gold.
-
-Pyrite is particularly the form in which the sulphur compounds of iron
-appear in rocks which have been highly heated, and is to be expected in
-metamorphic rocks and also igneous rocks, especially in fissures and
-veins leading from the igneous rocks. It may occur in sedimentary rocks,
-but in these last it is usually marcasite.
-
-
-Marcasite
-FeS₂
-Pl. 15
-_white pyrite_
-
-Occurs in orthorhombic crystals, usually grouped to make fibrous or
-radiating masses, or non-crystalline in masses; hardness 6; specific
-gravity 4.8; color pale brassy-yellow; streak greenish-gray; luster
-metallic; opaque on thin edges.
-
-Marcasite has the same chemical composition, as pyrite, and looks like
-it, but is lighter colored and usually occurs in fibrous masses. It is
-the commoner form in limestones and shales, while pyrite is more likely
-to occur in igneous and metamorphic rocks. It seems probable that
-marcasite is due to a more hasty precipitation from cold solutions,
-while pyrite is deposited more slowly from hot solutions.
-
-Isolated crystals of marcasite are rare; but, if formed, they belong to
-the orthorhombic system. Usually some form of twinning is present, and
-because of the multiple character of the twinning, marcasite crystals
-usually show a ragged outline, with reentrant angles. It is most
-abundant in radiated masses, which appear fibrous on the broken
-surfaces. It decomposes easily, taking oxygen from the air and forming,
-even in museum cases, a white efflorescence or “flower,” which is iron
-sulphate or melanterite. In moist air it takes water and decomposes to
-sulphuric acid which may change the surrounding limestone to gypsum.
-Marcasite is found wherever limestones and shales are the country rock.
-
-
-Pyrrhotite
-Fe₁₁S₁₂
-_Magnetic pyrites_
-
-Occurs in masses; hardness 4; specific gravity 4.6; color bronze; streak
-grayish-black; luster metallic; opaque on thin edges.
-
-Tabular crystals are known, but are very rare. They belong to the
-hexagonal system. This form is easily distinguished from the other
-yellow minerals by being magnetic. It is by no means as abundant as the
-two preceding sulphides of iron, but does occur fairly frequently in
-veins in igneous rocks, and less frequently in limestones, large
-quantities of sulphuric acid being made from a deposit in limestone at
-Ducktown, Tenn. It will be found in most states. When associated with
-nickel it is an important source for the latter mineral, as at Sudbury,
-Canada. Pyrrhotite is very like a substance found in meteorites, known
-as troilite.
-
-
-                             The Lead Group
-
-After learning how to get iron from the rocks by rude smelting methods,
-the early peoples tried heating various rocks, and some time around 500
-B.C. stumbled upon lead, which is rather easily separated from its ores.
-This metal was used through Roman times to make pipes, gutters, etc.
-
-Lead is a soft metal, fairly malleable, but with little ductility, and
-still less tensile strength. Though one of the commoner metals, it does
-not occur as pure metal in Nature. It is diffused in minute quantities
-through the igneous rocks, and also is found in the sedimentary rocks
-and in the sea water. Its minerals are few, galena, the sulphide of
-lead, being the commonest, and at the same time the form in which lead
-is primarily deposited. Galena may also represent a secondary
-deposition. The other minerals, cerrusite, anglesite, and pyromorphite
-are results of modification of the galena when it lies near enough to
-the surface to be acted on by weathering agents, like water and air.
-Lead minerals are usually associated with zinc minerals, there being but
-few places where the minerals of the one group occur without the other.
-Most lead when first smelted from its ore, contains a greater or less
-amount of silver in it, sometimes enough so that the lead ore is better
-worth working for the silver than for the lead.
-
-Lead is used in making pipes, gutters, bullets, etc., and in its oxide
-forms in the manufacture of paints and glass. Eighty-three parts of lead
-with 17 parts of antimony make type metal. Lead and tin alloy to make
-solder. Lead and tin with small amounts of copper, zinc and antimony
-make pewter. The United States produce about 20% of the world’s supply
-of this metal.
-
-
-Galena
-PbS
-Pl. 17
-_lead glance_
-
-Occurs in cubes or cleavable masses; hardness 2.5; specific gravity 7.5;
-color lead-gray; streak lead-gray; luster metallic; opaque.
-
-While there is quite a group of lead-gray minerals, galena is easily
-identified by its cleavage, which is perfect in three directions
-parallel to the cube faces. Even a moderate blow of the hammer will
-shatter a mass of galena into small cubic pieces. The crystals often
-have the corners cut by octahedral faces, and occasionally the edges are
-beveled by dodecahedral faces. It is not uncommon to find crystals of
-large size, several inches across. If galena has 1 to 2% of bismuth as
-an impurity, curiously enough, the cleavage changes to octahedral, but
-this is a rare occurrence.
-
-Galena may occur as a primary mineral in veins associated with igneous
-intrusions, or in irregular masses in metamorphic rocks; but it is more
-often found in irregular masses in limestones, where the limestone has
-been dissolved, and the cavities thus formed, filled with secondary
-deposits of galena. It also occurs at the contact between igneous rocks
-and the adjacent rock, whatever this may be. Sometimes it is found in
-residual clays.
-
-Among the most important lead deposits are the Cœur d’Alene district in
-Idaho, where galena with a high percentage of silver is mined; the
-Leadville, Colo., district where lead, silver and gold occur together in
-veins; the Joplin, Mo., district, where lead and zinc ores occur
-together in irregular masses in limestones; and the Wisconsin district
-of similar character.
-
-When found galena is usually associated with sphalerite, argentite
-chalcopyrite, pyrite and calcite. It will be found in every state.
-
-
-Cerrusite
-PbCO₃
-Pl. 18
-_White lead ore_
-
-Occurs in fibrous or compact masses, or in orthorhombic crystals,
-usually on galena; hardness 3.5; specific gravity 6.5; colorless; streak
-white; luster adamantine; transparent on thin edges.
-
-While the crystals of this mineral simulate hexagonal, they are actually
-orthorhombic, the simple form being an octahedron with two of its edges
-beveled, making double six-sided pyramids (see Pl. 18 A.) Usually prism
-faces are present. Twinning is common, both the simple contact sort, as
-shown on Plate 18 B, and also the sort in which three crystals have
-grown through each other, so as to make a six-rayed crystal. The
-considerable weight, and the fact that it effervesces in acid serve to
-identify cerrusite. When pure it is colorless, but impurities cause it
-to appear white, gray or grayish-black, and sometimes it has a tinge of
-blue or green.
-
-It is likely to occur wherever galena is found, as a secondary mineral
-derived from the galena. In this country it is not used as an ore, for,
-as in the Leadville district, veins which have cerrusite near the
-surface change at moderate depths, and galena takes the place of the
-cerrusite. It is found all down the Appalachian Mountains, and in all
-the Cordilleran States. Especially fine specimens have come from the
-Cœur d’Alene district in Idaho.
-
-
-Anglesite
-PbSO₄
-Pl. 18
-
-Occurs in grains and masses, or in tabular and prismatic orthorhombic
-crystals; hardness 3; specific gravity 6.3; colorless; luster
-adamantine; transparent on thin edges.
-
-Two modes of occurrence are characteristic, one in cavities in galena,
-the other in concentric layers around a nucleus of galena. In the former
-case fine crystals are developed, in the latter the mineral is in
-masses. The crystals look like those of barite, but are soluble in
-nitric acid while the barite is insoluble. Sometimes the crystals are
-prismatic with pyramidal faces instead of the tabular form.
-
-It is found in the lead mines associated with galena, and in this
-country is not used as an ore for lead, but in Mexico and Australia it
-is abundant enough to be mined as an ore. Exposed to water which has
-carbon dioxide in it, and most surface waters have some, it readily
-changes to cerrusite. It is found in Missouri, Wisconsin, Kansas,
-Colorado, and Mexico.
-
-
-Pyromorphite
-Pb₅Cl(PO₄)₃
-Pl. 17
-_Green lead ore_
-
-Occurs in small barrel-shaped hexagonal crystals, and in fibrous or
-earthly masses; hardness 3.5; specific gravity 7; color green to brown;
-luster resinous; translucent on thin edges.
-
-Pyromorphite is found in the upper levels of lead mines, and is formed
-by the decomposition of galena. Its green color (sometimes shading off
-toward brown), considerable weight and resinous luster, serve to
-distinguish this mineral. The crystal form is that of a simple hexagonal
-prism, with the ends truncated. It is found in Phœnixville, Penn.,
-Missouri, Wisconsin, Colorado, New Mexico, etc.
-
-
-                             The Zinc Group
-
-Zinc and copper made the brass of early Roman times; but even then, zinc
-was not known as a separate metal, the brass being made by smelting
-rocks in which both zinc and copper occurred, the zinc never being
-isolated until much later. Some time in the later Roman times it seems
-to have been obtained separately, but then and all down through the
-Middle Ages zinc and bismuth were confused. Our earliest record of zinc
-being smelted, as we know it today, was about 1730 in England. In those
-earlier days, the product, zinc, or bismuth, or both together, were
-known as “spelter,” and this name has clung to zinc in mining and
-commercial circles; so that today, if one looks for quotations in the
-newspaper, he often finds zinc under the head of spelter.
-
-Zinc, like lead, is diffused in small quantities through all the igneous
-rocks. In places it is segregated in fissures or veins leading from the
-igneous rocks, along the contact between igneous rocks and either
-sedimentary or metamorphic rocks, in limestones where solution cavities
-have been formed and later filled with zinc minerals, and as a residue
-where limestones have been weathered away. In all these places it is
-closely associated with lead.
-
-The sulphide, sphalerite, is the primary mineral, and the other
-minerals, like zincite, smithsonite, calamine, willemite, franklinite,
-etc., are secondary, resulting from modifications of the original
-sphalerite. In connection with zinc minerals the region of Franklin
-Furnace, N. J., is especially interesting, for at that place are found
-two large metamorphosed deposits containing a wide range of zinc
-minerals, several of which are not found anywhere else.
-
-Zinc is soft and malleable, but is only slightly ductile, and has little
-tensile strength. It alloys with several metals, and in this form is
-most useful today; three parts of copper to one of zinc making brass;
-four or more parts of copper and one of zinc, making “gold foil”; copper
-and zinc (a little more zinc than copper) making “white metal”; three
-parts of copper to one of zinc and one of nickel making German silver;
-etc. Zinc is also used in large quantities in galvanizing iron, sheets
-of iron being dipped into melted zinc and thus thinly coated. It is also
-used in batteries and a wide range of chemical industries.
-
-
-Sphalerite
-ZnS
-Pl. 19 & 20
-_zinc blende, black jack_
-
-Occurs in grains, in fibrous or layered masses, or in isometric
-crystals; hardness 3.5; specific gravity 4; color yellow-brown to almost
-black; streak light yellow to brownish; luster resinous to adamantine;
-translucent on thin edges.
-
-When in crystals sphalerite occurs most commonly either in dodecahedrons
-or in tetrahedrons (hemihedral forms of the isometric octahedron). The
-cleavage is fairly good and parallel to the faces of the dodecahedron.
-The difficulty usually is to get large enough crystalline masses to see
-this cleavage clearly, but by examining the angles between the faces of
-cleavage pieces they will be found to be the same as those on a
-dodecahedron. When the mineral is pure, it has the color of resin, but
-sometimes it is reddish to red-brown, and then it is called “ruby zinc,”
-more often it is dark brown due to the presence of iron as an impurity.
-This is what the miners call “black-jack.” The presence of iron also
-tends to make the streak darker. The hardness, streak and cleavage will
-usually determine this mineral readily.
-
-Sphalerite is the primary ore of zinc and is usually found in fissures
-and veins leading from masses of igneous rocks, or along the surface of
-contact where igneous rocks like granite or lavas come against such
-metamorphic rocks as gneisses, schists, or crystalline limestones. In
-the region of Joplin, Mo., however, the sphalerite is of secondary
-character, having been gathered by waters circulating through the
-limestones, and deposited in them in irregular pockets. This Joplin
-district has produced more zinc than any other in the world. The United
-States annually produces about 25% of the world’s supply of this metal.
-
-Sphalerite is always associated with galena, and such other minerals as
-argentite, pyrite, chalcopyrite, fluorite, quartz, calcite and barite,
-are very apt to be present. It will be found in almost every state,
-especially in fissures and veins, and less frequently in cavities in
-limestones.
-
-
-Zincite
-ZnO
-Pl. 19 & 20
-_red zinc ore_
-
-Usually occurs massive, but may be found in crystals; hardness 4;
-specific gravity 5.6; color deep red; streak orange; luster
-subadamantine; translucent on thin edges.
-
-When in crystals zincite forms in hexagonal prisms with hexagonal
-pyramids on the ends. This is rather rare, most of the zincite being
-found in massive form. The cleavage is parallel to the prism faces and
-perfect. The deep red color and orange streak are wholly characteristic.
-
-This mineral is so common at Franklin Furnace, N. J., as to be an
-important ore, but it is very seldom found elsewhere. This district, as
-mentioned before, is a peculiar one for zinc minerals. The zinc beds are
-in a metamorphosed limestone, and into this are intruded numerous dikes
-of granite. Probably the zinc was originally present in the bed of
-limestone as smithsonite, calamine and other secondary minerals of zinc.
-When intruded by the hot granite the smithsonite (carbonate) may well
-have been altered to the oxide, zincite; while the calamine (hydrous
-silicate) became the simple silicate, willemite.
-
-
-Willemite
-ZnSiO₄
-Pl. 20
-
-Occurs in masses or in crystals; hardness 5.5; specific gravity 4.1;
-color pale yellow when pure; luster resinous; translucent on thin edges.
-
-Willemite is another of the minerals which are distinctively
-characteristic of Franklin Furnace, and found elsewhere very rarely. It
-is so common there as to be one of the principal ores, and mostly occurs
-in irregular masses, but is also found in crystals. These are hexagonal
-prisms, with a three-sided (rhombohedral) pyramid on the ends. The color
-when pure is whitish or greenish-yellow, but with small amounts of
-impurities it may be flesh-red, grayish-white or yellowish-brown. When
-in crystals it is easily determined; but when massive it looks like
-calamine, and can only be distinguished by placing a bit of the mineral
-in a closed tube and heating it, in which case calamine will give off
-water vapor, while willemite will not.
-
-This mineral is one of those resulting from metamorphic alteration and
-is derived from calamine, when the latter loses its water of
-crystallization. It is common at Franklin Furnace, N. J., and also found
-occasionally elsewhere, as at Salida, Colo., and in Socorro Co., New
-Mexico.
-
-
-Calamine
-Zn₂(OH)₂·SiO₃
-
-Occurs as crystalline linings in cavities, or as botryoidal or
-stalactitic masses; hardness 5; specific gravity 3.4; colorless to
-white; luster vitreous.
-
-Calamine resembles both smithsonite and willemite when in
-non-crystalline masses. From the smithsonite it is easily separated by
-the fact that in nitric acid the smithsonite effervesces and the
-calamine does not. From willemite it is harder to distinguish, but a
-piece may be placed in a closed tube and heated. If it is calamine water
-vapor will be given off, if willemite nothing happens. When calamine
-occurs in crystals these are orthorhombic and mostly tabular, and the
-crystals are peculiar in that the two ends are terminated differently.
-
-Both this and smithsonite are secondary minerals and usually occur
-together when zinc is found in limestones. It is abundant at Franklin
-Furnace and Sterling Hill, N. J., and also found at Phœnixville, Penn.,
-in Wythe Co., Va., and Granby, Mo.
-
-
-Smithsonite
-ZnCO₃
-Pl. 21
-_Dry bone_
-
-Usually occurs as incrustations, grains, earthy or compact masses, and
-as crystals; hardness 5; specific gravity 4.4; color white, yellow,
-greenish or bluish; streak white; luster vitreous; transparent on thin
-edges.
-
-When pure this mineral is colorless, but, as it occurs, it is usually
-white, or tinged with some shade of yellow, green, or blue, but in all
-cases its streak is white. The crystals are rhombohedrons often with
-edges beveled or corners cut by other faces. It resembles calamine and
-willemite, but is readily separated from either of these by the acid
-test, for smithsonite effervesces when acid is placed on it.
-
-Next to sphalerite, smithsonite is the commonest of the zinc minerals.
-It is a secondary mineral, resulting from the action of lime-charged
-water acting on sphalerite, and so is likely to be found wherever zinc
-minerals occur in a limestone region. In the Wisconsin-Illinois-Iowa
-district it serves as a minor ore of zinc, and is termed here “dry
-bone.” It is also found in the Missouri and Arkansas districts, and in
-Europe is an important ore for zinc.
-
-
-Franklinite
-(ZnMn)Fe₂O₄
-Pl. 21
-
-Occurs in compact grains or masses, and in isometric octahedrons;
-hardness 6; specific gravity 5; color black; streak reddish-brown;
-luster metallic; opaque on thin edges.
-
-This is a mineral peculiar to the Franklin Furnace region, from which it
-gets its name. It looks like magnetite, but its reddish-brown streak and
-lack of magnetism distinguish it. When it occurs in octahedrons, the
-edges are rounded, while those of magnetite are sharp. It is a complex
-and variable oxide of zinc, iron and manganese, which has resulted from
-the metamorphism of the beds in which it occurred probably being
-originally something quite different.
-
-
-                          The Manganese Group
-
-Though manganese was known in the mineral pyrolusite in early times, it
-was then thought to be magnetite or magnetic iron ore. It was not until
-1774 that it was isolated and recognized as a distinct element.
-
-Manganese is one of the lesser elements in the crust of the earth,
-making less than .07 of one percent, but as an alloy with other metals,
-especially iron, it has attained a considerable importance to man. It is
-used chiefly with iron, 20% of manganese making the alloy, spiegeleisen,
-a combination which occurs in Nature in Germany, and from 20% to 80%
-making ferromanganese. These alloys are in great demand because they
-make an especially tough steel essential in the manufacture of
-munitions. The sources for manganese are the oxide ores, manganite,
-pyrolusite and psilomelane, which have been formed as secondary
-minerals, as a result of the weathering of silicates which carry
-manganese. They occur widely enough, but throughout the United States
-the deposits are small, and this is one of the elements in which this
-country is not self-sufficient. The largest producer of manganese is
-Russia; however she consumes almost all of her output at home, and our
-supply comes from the next largest producers, India, the Union of South
-Africa, and the Gold Coast. A shift in trade may be expected when
-Brazil’s recently discovered ore body in Matto Grosso is brought into
-full production. Besides being used as an alloy, manganese is employed
-in making paints and dyes, for clearing glass, and for some types of
-electric batteries.
-
-
-Pyrolusite
-MnO₂
-
-Occurs in earthy or fibrous masses; hardness 1-2; specific gravity 4.8;
-color black; streak black; luster dull; opaque.
-
-Pyrolusite occurs in soft masses and incrustations, usually leaving a
-sooty mark on the fingers. Sometimes it seems to be in crystals, but
-these are pseudomorphs which have the form of manganite, from which the
-pyrolusite has formed as a result of the water having been driven from
-the manganite. Frequently pyromorphite and manganite will be found
-together, and in some cases the outer part of a mass or crystal will be
-pyrolusite, while the center is still manganite. Psilomelane is another
-oxide of manganese with water and may appear very like pyrolusite, but
-both manganite and psilomelane have much greater hardness than does
-pyrolusite. If there is difficulty in deciding about pyrolusite, it may
-be placed in a closed tube and heated. It will not be affected by the
-heat, while, under the same circumstances, both manganite and
-psilomelane will give off water vapor.
-
-Pyrolusite usually occurs in black streaks or pockets in residual clays
-which have formed as a result of the decomposition of limestones. It may
-also occur in dendritic forms in seams and crevices (see manganite). It
-is found in Vermont, Massachusetts, Virginia, Arkansas, Colorado,
-California, etc.
-
-
-Psilomelane
-MnO₂·H₂O
-
-Occurs in compact botryoidal or stalactitic masses; hardness 5-6;
-specific gravity 4.2; color black; streak brownish-black; luster
-metallic; opaque on thin edges.
-
-Psilomelane is very like pyrolusite, and often occurs with it. It is
-distinguished by its greater hardness, and the fact, that when heated in
-a closed tube, it gives off water vapor. From manganite it is more
-easily distinguished, for it never occurs in crystals, while the
-manganite is usually crystalline. This and pyrolusite are the principal
-ores of manganese.
-
-Wad is an impure form of psilomelane, having some iron oxide mixed with
-the manganese oxide, usually limonite; or the impurity may take the form
-of a copper, cobalt, lithium or barium oxide.
-
-Psilomelane is found at Brandon, Vt., in Arkansas, Colorado, California,
-etc.
-
-
-Manganite
-Mn₂O₃·H₂O
-Pl. 22
-
-Occurs in prismatic crystals, or in columnar or fibrous masses; hardness
-4; specific gravity 4.4; color steel gray; streak reddish-black; luster
-submetallic; opaque on thin edges.
-
-This is the form taken by manganese oxide when it crystallizes in the
-presence of moisture, and pyrolusite frequently changes to manganite
-when exposed to moisture. The crystals are orthorhombic prisms, with
-striated sides and the ends truncated. These prisms usually occur in
-bundles and give the mineral a fibrous appearance. Manganite is not hard
-to identify, the striations on the crystals and the streak being very
-characteristic.
-
-In seams and tiny crevices this mineral, and often pyrolusite, grows in
-a branching manner, resembling tree-like or “mossy” masses. This is
-termed dendritic, and the growths of manganese minerals are called
-dendrites. One of the most curious of these is when the “mossy” growth
-is inclosed in chalcedony, making the so-called _moss agate_. These moss
-agates are abundant through the Rocky Mountains and are frequently cut
-for semi-precious stones. The finest ones however come from India and
-China.
-
-Manganite is found in the Lake Superior region, Colorado, etc.
-
-
-Rhodochrosite
-MnCO₃
-
-Occurs in compact cleavable masses; hardness 4; specific gravity 3.5;
-color rose to dark red; streak white; luster vitreous; translucent on
-thin edges.
-
-This usually occurs in pink to red masses which cleave readily parallel
-to the faces of the rhombohedron. When it is found in crystals, which
-are rare, these too are rhombohedrons. It is usually found in veins as a
-gangue mineral with copper, silver or zinc ores. Its beautiful color and
-the fact that it effervesces in acid serve to distinguish this mineral.
-It is found at Branchville, Conn., at Franklin Furnace, N. J., and in
-veins with silver in Colorado, Nevada, and Montana.
-
-
-                           The Aluminum Group
-
-Though aluminum is one of the most abundant of all the metals, making
-some 8% of the crust of the earth, its union with other elements is so
-firm, that only recently have methods been found for getting the metal
-free. It was first isolated in 1846, but up to 1890 the extraction of
-aluminum was so expensive, that it could not be widely used. About that
-time electrical processes were applied to its extraction, and since then
-the price has steadily dropped, until now it is under $.20 per pound. It
-is very malleable, and ductile, and has high tensile strength. Exposed
-to the air, water or ordinary gases, it does not tarnish; and it is very
-light, an equal bulk weighing about a third as much as iron. The
-combination of lightness and strength, and the fact that it is a good
-conductor of electricity, have made it available for a wide range of
-uses, such as electrical apparatus, delicate instruments, boats,
-aeroplanes, and domestic utensils.
-
-It is an essential component of all the important rocks, except
-sandstone and limestone, and combines to a greater or less degree in a
-host of minerals. Though present in clays, shales, argillites,
-feldspars, and micas, it is only from bauxite that it has been
-successfully extracted. Aside from the small number of simple compounds
-of aluminum grouped here, it also takes a part in the make-up of a large
-series of minerals termed silicates, treated a little further on in this
-book.
-
-It alloys with other metals, especially copper. The union of copper and
-a small amount of aluminum makes aluminum-bronze, which looks like gold
-and is used for watch chains, pencil-cases, etc., and also for the
-antifriction bearings of heavy machinery. A small amount added to steel
-prevents air holes and cracks in casting.
-
-
-Corundum
-Al₂O₃
-Pl. 23
-
-Occurs in cleavable masses or in hexagonal crystals; hardness 9;
-specific gravity 4; colorless, red, yellow, blue, or gray; luster
-vitreous to adamantine; translucent to transparent on thin edges.
-
-Corundum is readily recognized by its hardness, second only to that of
-the diamond. The crystals may be simple six-sided prisms, hexagonal
-pyramids or combinations of the two. The cleavage is usually described
-as parting, for it is by no means perfect, but when it is recognizable
-it is parallel to the faces of a rhombohedron, and cleavage pieces may
-appear almost cubic.
-
-When in clear and perfect crystals this mineral is one of the most
-highly prized of all the gems. Clear and colorless it is known as the
-“_Oriental white sapphire_”; when tinged with blue it is the _sapphire_;
-when colored yellow, the “_Oriental topaz_”; when green, the “_Oriental
-emerald_”; when purple, the “_Oriental amethyst_” and when red, the
-_ruby_. Sapphires range from colorless to deep blue, the value depending
-on the shade of the blue, and increasing as the color deepens. The
-Oriental topaz can easily be confused with the true topaz, which is a
-much commoner and less valuable gem, but can be distinguished by the
-hardness, topaz having a hardness of but 8. The name emerald is applied
-to several green gems, mostly to beryl, which is not so hard and is the
-true emerald. The Oriental emeralds have a value about the same as
-diamonds. Rubies of clear and deep color are the rarest of all gems,
-ranging in value about three times as high as diamonds of equal size.
-The most sought-for shade is the so-called “pigeon-blood red,” and the
-value of a stone of this sort is almost dependent on the whim of the
-buyer. The best of the rubies come from granites or metamorphosed
-limestones in Burma; the best sapphires from Ceylon, though both of
-these, and some of the other corundums of gem quality, have been found
-in North Carolina and Montana.
-
-Around these stones, which have been used so long among the Hindus,
-Persians, Jews, Egyptians, and Christians, a wealth of lore has been
-woven. The sapphire was Saturn’s stone, and a talisman to attract Divine
-favor. Where tradition makes the stone on which the ten commandments
-were written the sapphire, it is probable that, what was really meant,
-is lapis lazuli, as is also the case when sapphires are mentioned as
-building stones for the celestial gates. The ruby in ancient lore is
-termed “lord of stones,” “gem of gems” etc., and so protected its wearer
-that he was safe from injury in peace or war.
-
-When corundum is colored brown by impurities of iron, it is termed
-_corundum_, when black by greater quantities of iron, it is _emery_.
-These varieties are far the commonest form in which corundum occurs, and
-when ground to finer or coarser powder make the commercial emery. Emery
-is likely to be found in sands, making so-called “black sands,” where it
-has accumulated as a result of the weathering to bits corundum-bearing
-rocks. In some one of its forms, corundum is found in Massachusetts,
-Connecticut, New York, New Jersey, and all down the Appalachian
-Mountains, also in Colorado, Montana, California, etc.
-
-
-Bauxite
-Al₂O₃·2H₂O
-
-Occurs in grains, or oolitic or clay-like masses; hardness 1-3; specific
-gravity 2.5; color white to yellowish-white or reddish-brown.
-
-Bauxite never comes in crystals, but is usually in earthy masses, which
-have resulted from the decomposition of granitic or volcanic rocks, in
-circumstances where hot alkaline waters were present. This explanation
-seems to apply especially to the deposits in France, which were first
-the chief source of the bauxite, and may be applicable to those in
-Georgia and Alabama. Some of the other deposits, however, do not seem to
-have had any hot water available, and the deposit appears more like
-simple decomposition of the underlying rocks by alkaline waters.
-
-In many cases bauxite resembles limonite in being a mixture of two or
-more aluminum oxides with water of crystallization, such as Al₂O₃·H₂O,
-Al₂O₃·2H₂O and Al₂O₃·3H₂O. This is particularly true of the bauxite
-which resulted from the decomposition of rocks by surface water.
-
-Bauxite is the ore from which aluminum is obtained. The deposits are not
-large, but the United States has its share of them. It is found in
-Alabama, Arkansas, Georgia, Missouri, Tennessee, and California.
-
-
-Cryolite
-Na₃AlF₆
-_Ice stone_
-
-Occurs in pseudo-cubic crystals or massive; hardness 2.5; specific
-gravity 3; color white; luster vitreous; transparent on thin edges.
-
-Cryolite is a relatively soft mineral, colorless to white as snow; for
-which reason, and partly also because it comes mostly from Greenland it
-is called “ice stone.” It is really monoclinic but the inclination of
-the c axis is so slight, that, unless examined carefully, the crystals
-appear to be cubic. Until about 1900 great quantities of this mineral
-were shipped from West Greenland, and from them the metal aluminum was
-extracted. When bauxite was discovered, it was found to be considerably
-cheaper to make the aluminum from that mineral, and now cryolite is no
-longer sought. Aside from its occurrence in Greenland some cryolite is
-found in Colorado, near Pike’s Peak.
-
-
-                           The Arsenic Group
-
-The metal, arsenic, is a dark steel gray in color, when the surface is
-fresh, but it soon tarnishes. It is very brittle and easily powdered
-under the hammer, and its only use as a metal, is for an alloy with lead
-in making shot. Its compounds find a wider use. The white powder called
-“arsenic” is arsenous acid, and is used mostly in making poisons, which
-fortunately are easily detected in animal tissues. Copper arsenate,
-(_Scheele’s green_) is a pigment used in making green paint, and
-formerly in the green colors of wall paper. A combination of arsenous
-acid, copper oxide and acetic acid is the well known _Paris Green_, so
-much used for an insecticide. Beside these uses, arsenic serves a large
-number of other purposes, as in making glass and enamel, embalming
-fluids, and various medicines.
-
-Curiously arsenic plays a double part, acting part of the time as a
-metal, as in the two following minerals, and part of the time as a
-non-metal, as in cobaltite, niccolite, etc.
-
-
-Arsenopyrite
-FeAsS
-Pl. 24
-
-Occurs in well formed crystals, grains, or masses; hardness 5.5;
-specific gravity 6; color silver-white; streak black; luster metallic;
-opaque on thin edges.
-
-When in crystals, they are usually short prisms of the orthorhombic
-system, either end being terminated with a low roof. Though usually
-described as silver-white in color, there is always a brassy cast to the
-color. Its appearance is much like cobaltite and smaltite, but it can be
-easily distinguished from both these by putting a piece in nitric acid.
-The arsenopyrite will not materially change the color of the fluid, but
-the other two turn it rose-red, and all give off the smell of sulphur.
-It looks sometimes like marcasite, but that is yellower, and has the
-fibrous structure, not found in arsenopyrite.
-
-It is found in veins or in metamorphic rocks, associated with argentite,
-galena, sphalerite, chalcopyrite and pyrite. It is distinctly a mineral
-formed by deposition from hot vapors or hot water rising from either
-lavas, or in the course of metamorphism.
-
-It is found in New Hampshire, Vermont, Massachusetts, Connecticut, New
-York, New Jersey, California, etc.
-
-
-Realgar
-AsS
-Pl. 24
-
-Occurs in incrustations or scattered grains; hardness 1.5 to 2; specific
-gravity 3.5; color orange; streak orange; luster resinous; opaque on
-thin edges.
-
-Crystals are very rare, but when found are short monoclinic prisms. The
-color is aurora-red, changing to orange as soon as it is exposed to the
-air. This and the streak are entirely characteristic. It is a mineral
-associated with hot vapors or hot waters, and is found about volcanoes,
-as deposits from the hot water of the geysers in Norris Basin,
-Yellowstone Park, and in veins, associated with barite, stibnite,
-quartz, etc., as in Massachusetts, Utah, California, etc.
-
-
-Orpiment
-As₂S₃
-
-Occurs as incrustations or powdery masses; hardness 1 to 2; specific
-gravity 3.5; color lemon yellow; streak yellow; luster resinous.
-
-This mineral is very like realgar in its physical properties, and likely
-to occur with it. It gives the lemon yellow color to the basins about
-hot springs, as in the Yellowstone Park, and about volcanoes. It also
-comes in veins with realgar.
-
-
-                               Molybdenum
-
-Molybdenum is a rare metal, silvery-white in color, brittle and very
-difficult to fuse. It is used mostly as an alloy of steel, to make
-certain grades of tool steel. The world’s greatest supply is obtained
-from Climax, Colorado, where the principal ore mineral is molybdenite.
-
-
-Molybdenite
-MoS₂
-
-Occurs in scales or scaly masses, occasionally in tabular hexagonal
-crystals; hardness 1.5; specific gravity 4.7; color lead-gray; streak
-bluish-gray; luster metallic; opaque.
-
-This mineral is the chief source for the metal molybdenum. Its extreme
-softness and greasy feel will distinguish it at once from any other
-mineral except graphite, which has much the same qualities, but its
-scaly character and the more bluish tinge in streak and color will
-distinguish these two.
-
-It occurs in granites, gneisses, and metamorphic rocks in Colorado, New
-Mexico, Maine, Connecticut, New Hampshire, New York, Pennsylvania, etc.
-
-
-                                Antimony
-
-Antimony is another hard, brittle metal, of bluish-white color. Exposed
-to the air at ordinary temperatures it does not tarnish; and this
-combined with its hardness make it useful for such alloys as Britannia
-metal, type metal, and pewter. Only one of its minerals, stibnite, is
-common enough for mention.
-
-
-Stibnite
-Sb₂S₃
-Pl. 25
-_gray antimony_
-
-Occurs in prismatic or needle-like crystals; hardness 2; specific
-gravity 4.5; color lead-gray; streak lead-gray; luster metallic; opaque.
-
-The crystals of stibnite are orthorhombic and usually elongated, the
-sides striated and the ends with low pyramids on them. Sometimes the
-long crystals are curved or even twisted. There is a well-developed
-cleavage parallel to face b in the figure. While the color is similar to
-that of galena, the form and cleavage are so different that stibnite is
-easily determined.
-
-The ancients used stibnite to color their eyebrows, now it is the source
-for the metal antimony. Hungary and Japan are famous for the fine large
-crystals they produce; but moderate sized crystals may be found in this
-country. It occurs in veins along with pyrite, galena, cinnabar, and
-realgar, with quartz, calcite or barite as gangue minerals.
-
-Stibnite has been found in Arkansas, California, Nevada, and Utah.
-
-
-                            The Nickel Group
-
-Nickel as a metal is silvery-white in color, rather hard, and does not
-tarnish when exposed to the air. When pure it is malleable and fairly
-ductile. It is highly useful for plating other metals to protect their
-surfaces. Alloyed with steel, it makes a product of extreme hardness.
-Copper, zinc, and nickel make the well known German silver.
-
-Nickel has a fairly large range of minerals, but they do not occur with
-any abundance in the United States, so that we have to import most all
-of our nickel. In the earlier days New Caledonia produced most of the
-world’s supply, but recently since the finding of large nickel deposits
-near Sudbury, Canada, this locality has not only outstripped New
-Caledonia, but now produces four-fifths of the world’s supply. In this
-country but two nickel minerals will be found at all common.
-
-
-Niccolite
-NiAs
-Pl. 25
-_copper nickel_
-
-Occurs in masses; hardness 5.5; specific gravity 7.4; color pale
-coppery-yellow; streak pale brownish-black; luster metallic; opaque on
-thin edges.
-
-Niccolite is very seldom in crystals, but if they do occur they are
-hexagonal. The mineral looks a little like smaltite, but in case there
-is any question of the determination, dissolve a piece in nitric acid,
-and if niccolite, it will color the solution green.
-
-Niccolite is usually associated with copper and silver ores, and in this
-country has been found at Chatham, Conn., and Silver Cliff, Colo. It may
-be associated with pentlandite, a sulphide of iron and nickel, which is
-similar in appearance, but not so hard, and occurs in small grains
-throughout dark lavas. The particles of pentlandite are however so
-small, that they are seldom noticeable, but at Sudbury, Canada, this is
-the chief ore of nickel.
-
-
-Millerite
-NiS
-_capillary pyrites_
-
-Occurs in needle-like or fibrous crystals; hardness 3.5; specific
-gravity 5.5; color brass-yellow; streak greenish black; luster metallic;
-opaque on thin edges.
-
-The fibrous crystals of millerite belong to the orthorhombic system. The
-color and streak suggest pyrite, but the crystals are long and slender,
-while pyrite is in cubes, octahedrons, etc. If there is any doubt of the
-identity of this form, place a piece in nitric acid, and if it is
-millerite, it will color the acid green.
-
-It may occur in veins associated with cobalt and silver minerals, or as
-a secondary mineral as at Gap Mine, Penn., or in cavities in sedimentary
-rocks. In the last case it usually is in needle-like crystals growing
-through calcite crystals, as at St. Louis, Mo., Keokuk, Iowa, and
-Antwerp, N. Y.
-
-
-                            The Cobalt Group
-
-As a metal, cobalt is hard, brittle, and of a grayish color, tinged with
-red. It was not recognized as a separate element until 1735, and even
-today is one of the minor metals. Cobalt, chromium and a little tungsten
-make the alloy stellite, which has come into large use in making
-high-speed tools. The oxide of cobalt (CoO) is “smalt,” used to give the
-blue color to porcelain, pottery, glass, tiles, etc. Invisible ink is
-made by diluting cobalt chloride in a large quantity of water. This
-solution is a faint pink color and practically invisible on paper, but
-if heated it loses water and turns blue in color, and is perfectly
-visible.
-
-Cobalt is another of the metals, of which the United States does not
-have an adequate supply. Sweden, Norway and India were the chief sources
-of supply until cobalt was found near the town of Cobalt in Ontario,
-Canada, and now this district furnishes 90% of the world’s supply.
-
-
-Cobaltite
-CoAsS
-Pl. 26
-_cobalt glance_
-
-Usually crystalline in cubes, pyritohedrons or octahedrons; hardness
-5.5; specific gravity 6.1; color reddish silver-white; streak
-grayish-black; luster metallic; opaque on thin edges.
-
-In color cobaltite may appear very like arsenopyrite, especially if the
-reddish tinge is not strong, in which case the mineral can be definitely
-determined by putting a piece in nitric acid. If it is cobaltite the
-solution will be colored rose-red, if arsenopyrite there will be no
-change of color. The forms of the crystals are the same as those of
-pyrite, but the color will easily distinguish cobaltite from pyrite.
-This pink color is characteristically present either in or about cobalt
-minerals, being sometimes called “cobalt bloom.” It is a
-cobalt-arsenic-oxide with water of crystallization (Co₃As₂O₈·8H₂O),
-which results from the exposure of cobalt and arsenic minerals to air
-and moisture. It is the pink color on the figures of both cobaltite and
-smaltite. In Sweden, Norway and India, this is the chief ore for cobalt,
-but in the United States it is rather rare, but is found in Oregon, and
-at Cobalt, Canada.
-
-
-Smaltite
-(CoNi)As₂
-Pl. 26
-_gray cobalt ore_
-
-Usually occurs in masses; hardness 5.5; specific gravity 6.2; color
-tin-white to steel-gray; streak grayish-black; luster metallic; opaque
-on thin edges.
-
-While very like cobaltite, smaltite is almost never found in crystals,
-but when crystals are found, they are cubes. The color is tin-white but
-there is usually a pink tinge visible due to the presence of small
-amounts of “cobalt bloom.” If in any doubt about the determination of
-this mineral, put a piece in nitric acid. If it colors the acid
-rose-pink, and is non-crystalline it is pretty surely smaltite; if the
-acid is not affected it is arsenopyrite.
-
-Smaltite is found in Kentucky, Missouri, Colorado, Idaho, California,
-and at Cobalt in Canada.
-
-
-                                Chromium
-
-This metal gets its name in recognition of the many colors (_chroma_
-“color”), in which its compounds appear. Chromic oxide is a vivid green,
-used to color porcelains, pottery, tiles, etc., and also as a substitute
-for the arsenical greens formerly used in wall-paper. The chromate of
-lead is the pigment, well known to artists as “chrome yellow,” and the
-bichromate of potassium is bright red. The metal is obtained in at least
-two different forms; one hard, brittle and so resistant to heat as to be
-infusible at temperatures which would volatilize platinum; the other as
-a powder which burns brightly if heated in air. While used in paints,
-dyes, etc., its greatest importance is for the making of ferro-chrome
-steel, which is used where resistance to sudden shock is required, as in
-armor plate, automobile springs, ball bearings, etc. With tungsten and
-cobalt it makes the alloy, stellite, as noted above.
-
-Chromium was used in relatively small quantities before the first world
-war, and we imported our supplies from Turkey, India, New Caledonia, and
-Rhodesia. During the last war we started a large-scale development of
-low-grade ores in Montana, and can now supply all of our needs from this
-source.
-
-
-Chromite
-FeCr₂O₄
-_chromic iron_
-
-Occurs in grains, masses, or isometric octahedrons; hardness 5.5;
-specific gravity 4.4; color black; streak dark-brown; luster
-submetallic; opaque on thin edges.
-
-In form, color and streak chromite resembles magnetite and franklinite.
-From the magnetite it is distinguished by being non-magnetic; from the
-franklinite, by being insoluble in hydrochloric acid, while the
-franklinite is soluble. Chromite furnishes practically all the chromium
-used in the arts and manufactures. It is a mineral associated with high
-temperatures, and therefore found in dark lavas, serpentine, and
-olivine. It occurs in Pennsylvania, Maryland, New Jersey, Montana,
-Oregon, Wyoming, and California.
-
-
-                                Tungsten
-
-This element is obtained either as a heavy dark-gray metal, which is
-very hard and difficult to fuse, or as a dark-gray powder. It is used as
-an alloy with iron, one part of tungsten to nine of steel, to make the
-ferrotungsten, which has extraordinary hardness, and is used mostly for
-high-speed tools. Tungsten is also one of the three metals (cobalt,
-chromium and tungsten) which are alloyed together to make stellite. Some
-of the tungsten supply is also used to make the films in incandescent
-lamps, and in some of the chemical industries. It has but one important
-ore, wolframite, and this is found in the United States in but small
-quantities; so that we ordinarily have to import the greater part of
-what we use. During the last war, under the stimulus of high prices and
-the urge of necessity, we did find and produce substantial quantities of
-tungsten. China is the world’s largest producer of tungsten ore with
-Burma second, and the United States a poor third.
-
-
-Wolframite
-(FeMn)WO₄
-
-Occurs in monoclinic crystals or in crystalline masses; hardness 5.5;
-specific gravity 7.4; color dark-brown to black; streak nearly black;
-luster submetallic; opaque on thin edges.
-
-If in crystals the form will serve to distinguish this mineral from
-cassiterite and ilmenite, the two which it most resembles; but if it is
-massive the only sure way to decide is to put a piece in strong
-sulphuric acid; if it dissolves and throws down a yellow precipitate
-(tungstic acid) it is wolframite.
-
-Like the two other minerals mentioned above it occurs in veins in
-igneous rocks, being associated with high temperatures. As it is almost
-insoluble in water, like cassiterite and ilmenite, it is likely to occur
-with them in the sands which are the result of the disintegration of the
-rocks which carried the minerals; and so a large part of the supply
-today comes from placer deposits.
-
-It is found in Connecticut, North Carolina, Missouri, Colorado, and
-California.
-
-
-                      Radium, Uranium and Vanadium
-
-These three metals are all rare and occur together. Radium, discovered
-in 1898, is a heavy metal which has proved very useful because of its
-radio-activity, that is, its power of giving off or radiating tiny
-particles of matter known as _X-rays_, part of which are charged with
-positive electricity, and part of them with negative electricity. The
-ability of these rays to pass through other substances has made possible
-photographing the denser substances within those less dense, as the
-bones within the flesh, or metal within leather or wood, etc. The rays
-have proved of great value medicinally, and are also used to make
-objects luminous in the dark. These X-rays are also used in the study of
-the ultimate structure of matter, as it can be thus obtained in such
-small units.
-
-Uranium is another element which is radio-active and can be used for
-many of the same purposes as radium.
-
-Vanadium, the third of these associated metals, and the commonest of the
-group, is not radio-active. It is a silvery-white metal, mostly used as
-an alloy with steel to give it great hardness.
-
-
-Carnotite
-K₂O·2U₂O₃·V₂O₅·3H₂O
-Pl. 27
-
-Occurs in earthy masses; color yellow.
-
-This mineral is included here, not because it is common, but because it
-is of such great interest. It is the chief source of supply in the
-United States of radium, uranium and vanadium. It is a lemon-yellow
-earth or powder, which looks a little like orpiment. It is however found
-in a sandstone, instead of where hot waters have deposed minerals. From
-a ton of this ore about 10 pounds of uranium oxide, 55 pounds of
-vanadium and ¹/₁₀₀₀th of a gram of radium are obtained. Carnotite is
-found in south-west Colorado and south-east Utah, and on Carrizo
-Mountain on the line between Arizona and New Mexico.
-
-
-                                Mercury
-
-Mercury, or quicksilver, is the only metal which is liquid at ordinary
-temperatures. It is silvery-white in color, with a striking metallic
-luster, and at the low temperature of 662° F., boils and changes to a
-colorless vapor. Mercury alloys with certain metals, these alloys being
-known as amalgams. In this way it is especially useful for the recovery
-of gold and silver, the mercury being added to crushed ore, the gold or
-silver uniting with the mercury in a liquid amalgam, which is then drawn
-off and heated to a temperature above 662° F., at which temperature the
-mercury volatilizes and is recovered, while the gold or silver remains
-behind. Mercury also forms a solid amalgam with tin which is used to
-coat glass, the high metallic luster making the most effective looking
-glass. It is also used in medicines (calomel, corrosive sublimate,
-etc.), for scientific instruments (thermometers, barometers, etc.), in
-cosmetics, in paints for ship bottoms, etc.
-
-Though there are some 25 minerals of mercury, only one is common or
-important as a source of the metal, cinnabar. The United States is
-self-sufficient as far as mercury is concerned, producing just about as
-much as it uses. The leading producers are Spain, Austria, Italy, and
-the United States. Commercially mercury is quoted as quicksilver, and in
-flasks of 75 pounds each.
-
-
-Cinnabar
-HgS
-Pl. 27
-
-Occurs in massive or earthy form, or in minute crystals in cavities;
-hardness 2.5; specific gravity 8; color scarlet to dark red; streak
-vermilion; luster adamantine; translucent on thin edges.
-
-The bright-red color and the streak are usually enough to identify this
-mineral at once, but some of the darker varieties resemble hematite or
-zincite in appearance, but both these have much greater hardness. When
-in crystals they are tiny hexagonal prisms with pyramids on the end.
-Cinnabar is usually found in or near metamorphic or igneous rocks,
-either in veins leading from the igneous rocks, or in metamorphic rocks,
-or it may occur disseminated through metamorphic rocks. It is associated
-with quartz or calcite, and may occur with other sulphides like pyrite,
-galena, argentite, etc. It is most abundant in California, but is also
-found in Oregon, Washington, Idaho, Arizona, Nevada, Utah, Texas, and
-Montana.
-
-
-                                  Tin
-
-Tin has been known since early Roman times, and the mines at Cornwall,
-England, were worked from that time all through down to the present, but
-now they are becoming of minor importance as they approach exhaustion.
-The metal is silvery-white, does not easily tarnish, is malleable, but
-has little ductility and little tensile strength. Tin is mostly used in
-making tin plate, a thin sheet of steel covered with tin, the tin being
-only 1 to 2% of the total weight. This tin plate is mostly made into tin
-cans, and used as containers for food. Some tin is used in making
-solder, tin-foil, tubes for paste, vaseline, etc., and around 1000 tons
-per year for weighting silk. This “weighting” makes the silk heavier by
-about 25% and gives it a “rustle,” which, while much in evidence, is
-really indicative that the silk is not pure. The United States produces
-very little tin, most of the world’s supply coming from the Malay
-Peninsula, Dutch East Indies, China, and Bolivia, with small amounts
-from several other countries.
-
-
-Cassiterite
-SnO₂
-Pl. 28
-_tin stone_
-
-Occurs in tetragonal crystals, massive, or in grains and pebbles;
-hardness 6.5; specific gravity 7; color black or dark-brown; streak
-gray; luster adamantine; translucent on thin edges.
-
-The crystals are short prisms with pyramidal ends. Twinning is common.
-Cassiterite also occurs in fibrous masses, and when it is weathered from
-its original location, is so insoluble and hard, that it remains as
-grains and pebbles, making placer-deposits, from which today three
-quarters of the supply is obtained. If pure, the crystals would be
-colorless, but impurities of iron and titanium give it the dark-brown to
-black color. Cassiterite may appear very like rutile, the crystalline
-forms being identical, but the reddish tinge of color in the rutile will
-separate the two.
-
-Cassiterite is one of those minerals which result from deposition at
-very high temperatures, probably from vapors, and is found in the veins
-in igneous rocks, such as light-colored granites, gneisses, syenites,
-etc. While not mined in this country it is found in small quantities in
-Maine, Massachusetts, New Hampshire, Virginia, Alabama, Wyoming,
-Montana, and California.
-
-
-                                Titanium
-
-Titanium, as a metal, is a heavy, gray, iron-like powder, which is
-chiefly useful as an alloy with iron, giving it toughness, and
-preventing bubbles and cracks in casting. It is not as rare as some
-other metals which have found a wider use.
-
-
-Rutile
-TiO₂
-Pl. 28
-
-Occurs in tetragonal crystals, and in grains; hardness 6.5; specific
-gravity 4.2; color red to reddish-brown; streak yellowish-brown; luster
-metallic to adamantine; translucent on thin edges.
-
-Rutile usually occurs in crystals, which are either short and stout, or
-in needle-like crystals. Twinning is common. In form and general
-appearance it resembles cassiterite, but the reddish color, and the
-yellowish-brown streak will distinguish the rutile. It is found in
-similar rocks, granites, gneisses, syenites, and mica-schists, the two
-minerals cassiterite and rutile often occurring together. This is also
-true of the grains, which have been weathered out and are found in sands
-and gravels of placer deposits. It is found in small quantities in all
-the New England States, New York, and all down the Appalachian
-Mountains, especially at Graves Mountain, Ga., and in Arkansas and
-Alaska.
-
-
-Ilmenite
-FeTiO₃
-
-Occurs in granular masses, as black sand, or as tabular hexagonal
-crystals; hardness 5-6; specific gravity 4.7; color black; streak
-brownish-red to black; luster metallic; opaque on thin edges.
-
-When ilmenite occurs in crystals they are tabular and resemble hematite
-in its darker varieties, but the streak readily distinguishes the two.
-In masses it looks like magnetite, but the lack of magnetism serves to
-distinguish these two minerals. It is very likely to be associated with
-cassiterite, rutile, or magnetite in grains which have weathered out of
-the original rock, and have resisted solution and wear. Sands with a
-large amount of the above mentioned minerals are termed “black sands,”
-some of which are important for one or another of these minerals.
-
-Ilmenite is a mineral formed at high temperatures, and probably often
-deposited from hot vapors. It is found in granites, syenites, and
-gneisses. Among the better known localities are Orange, N. Y.,
-Litchfield, Conn., Florida, California, etc.
-
-
-                                Platinum
-
-This metal is steel-gray in color, very malleable and ductile, almost
-infusible and resists the action of acids. It is one of the “noble”
-metals, much rarer than gold, and so has become popular for jewelry. It
-is also used in the manufacture of sulphuric-acid, in nitrogen-fixation
-plants, for chemical utensils, in the electrical industries, and in
-dentistry. Platinum in its occurrence is associated with the certain
-other equally rare elements, like iridium, palladium and osmium. Its use
-has increased rapidly of late, but the supply has not kept up with the
-demand, so that, whereas in 1906 platinum and gold were about equally
-valuable, now the platinum brings about five times as much as the gold.
-
-
-Platinum
-Pt
-
-Occurs in grains or nuggets; hardness 4.5; specific gravity 19 (21 if
-pure); color steel-gray; luster metallic; opaque.
-
-This rare metal is mostly found in placer-deposits, often with gold. It
-comes originally from dark igneous rocks, like peridotite, pyroxenite,
-etc., and platinum is found to be associated with the nickel ores of
-Sudbury, Canada. While formerly 90% of the world’s supply of platinum
-came from placer mines in the Ural Mountains, today more than half is
-produced in Canada and about a fifth in Russia. In the United States it
-is found in California, Oregon, Nevada, and Alaska.
-
-
-                          The Magnesium Group
-
-Magnesium is a silvery-white metal, easily tarnished by exposure to
-moist air. Because of its light weight, less than twice the weight of
-water, and strength, it is being substituted for aluminum, especially in
-airplanes, where the question of weight is crucial. It is also used in
-automobile and ship production and other machine industries, and in the
-manufacture of flares and incendiary bombs. Magnesium is obtained
-chiefly from magnesite, dolomite, and in the United States as a result
-of a recently developed process, from sea water. Magnesium has a
-considerable number of minerals, of which three are taken up here and
-several more under the head of silicates, where both magnesium and
-silicon are combined in a mineral.
-
-
-Spinel
-MgAlO₄
-Pl. 29
-
-Occurs mostly as isometric octahedrons; hardness 8; specific gravity
-3.5; color, red, yellow, green, or black; streak white; luster vitreous;
-transparent on thin edges.
-
-This is a rather rare mineral, but, when in clear crystals is considered
-one of the gems. It was early confused with corundum, and the red
-variety called ruby, as it was found in the same gem-bearing sands in
-Ceylon, Burma, and Siam. However the form of the isometric octahedron as
-compared with the hexagonal prism of the corundum, together with the
-lesser hardness are sufficient to distinguish the two easily. The
-crystals are usually octahedrons, but may have the corners cut or the
-edges beveled. Twins are not uncommon.
-
-The standard color is a clear deep-red, and such a spinel is known in
-the gem trade as a _spinel-ruby_. If the color is rose-red, it is a
-_Balas ruby_; if orange, it is _rubicelle_, if of a violet tinge,
-_almandine_. When small quantities of other elements replace the
-magnesium, the color is greatly changed. For example a little iron
-present gives the crystals a dark-green to black color, and the spinel
-is known as _ceylonite_. If there is both iron and chromium present, the
-color becomes yellowish or greenish-brown, and this variety is
-_picotite_. When the impurities are iron and copper, the color becomes
-grass-green, and it is called _chlorospinel_. A form, in which the
-magnesium is completely replaced by iron, is black in color and termed
-_hercynite_, and occurs fairly abundantly in Westchester Co., N. Y. From
-Amity, N. Y., to Andover, N. J., there is a belt of granular limestone
-in which spinel of all colors is found. St. Lawrence Co., N. Y., is also
-a rich locality. Bolton, Mass., Newton, Sterling, and Sparta, N. J.,
-North Carolina, Alabama, and California all yield spinel.
-
-
-Magnesite
-MgCO₃
-
-Occurs in cleavable or compact porcelain-like masses; hardness 4;
-specific gravity 3.1; color white to gray; luster vitreous; translucent
-on thin edges.
-
-Magnesite is white and brittle, and cleaves perfectly parallel to the
-faces of the rhombohedron, but it seldom occurs in crystals. It will
-effervesce in warm hydrochloric acid and has some resemblance to
-calcite, but can be distinguished by the greater hardness. It is still
-more like dolomite, both having the same color and cleavage, both
-effervescing in warm hydrochloric acid; but the magnesite has half a
-point greater hardness and the porcelainous appearance. Magnesite is
-used in toilet preparations, paper making, and mixed with asbestos, as a
-covering for heating pipes.
-
-Magnesite is found in Massachusetts, Pennsylvania, Texas, and in large
-deposits in California and Washington.
-
-
-Dolomite
-(MgCa)CO₃
-Pl. 19 & 29
-
-Occurs in crystals, or in cleavable or granular masses; hardness 3.5;
-specific gravity 2.8; color white to pink or gray; streak white; luster
-vitreous; transparent on thin edges.
-
-Dolomite crystallizes in the hexagonal system, in rhombohedrons
-(hemihedral form), which are more or less modified by faces on the
-corners or edges. The cleavage is parallel to the rhombohedron, and it
-will effervesce in warm hydrochloric acid. Sometimes the crystal faces
-are curved, and when this is the case, dolomite is easily determined.
-Usually however dolomite resembles both calcite and magnesite. From the
-calcite it is distinguished by the greater hardness, and from magnesite
-by lesser hardness and not being porcelainous in appearance. Some of the
-commoner forms are shown on Plate 29, crystals like C being found
-embedded in anhydrite and gypsum.
-
-Magnesium is a common element and is likely to be present wherever lime
-is being deposited, so dolomite crystals are common, and much of the
-limestone is dolomitic.
-
-It may be found in almost any limestone section of the country. Some of
-the finest crystals of dolomite however come from Roxbury, Vt.,
-Smithfield, R. I., Hoboken, N. J., Lockport, Rochester, and Niagara
-Falls, N. Y., etc.
-
-
-                   Silicon, Silica and the Silicates
-
-Silicon is one of the non-metallic elements, and does not occur as such
-in Nature. When isolated it is either a dark-brown powder, or steel-gray
-crystals. However silicon is next to oxygen in its importance in making
-the crust of the earth. Forty-seven per cent of the surface rocks are
-composed of oxygen, and 28% of silicon, the latter appearing in a host
-of minerals. The oxide of silicon is termed silica (SiO₂), its crystal
-form being quartz, the commonest of all minerals. In non-crystalline
-form silica is also widely distributed, as chalcedony and opal, even
-appearing in the tissues of animals and plants, as in the feathers of
-birds, the shells of certain Protozoa (Radiolaria), the spicules of
-sponges; and in plants, as the shells of diatoms, and in the stalks of
-grasses, especially cereals and bamboo. Silica in the form of sand is
-widely used in making glass, porcelain, china, etc., and in the various
-cements.
-
-Then there are a considerable number of acids of silicon, which do not
-occur in Nature, but their salts do, and make a host of minerals, which
-are known as the silicates, such as mica, feldspar, hornblende, etc.
-Either as quartz, or as silicates, silicon is represented in most all
-the igneous and metamorphic rocks and in many of the sedimentary rocks.
-
-
-Quartz
-SiO₂
-Pl. 30
-
-Occurs as hexagonal crystals, or in grains or masses; hardness 7;
-specific gravity 2.65; colorless when pure; luster vitreous; transparent
-on thin edges.
-
-Quartz is not hard to identify. Its hardness and the crystal-form
-separate it from most all other minerals. It is the most common mineral,
-making 12% of the earth’s crust. The usual crystal form is a hexagonal
-prism with the sides horizontally striated, and a six-sided pyramid on
-one or both ends. This six-sided pyramid is really two rhombohedrons, a
-right-handed one and a left-handed one, so that the alternate faces of
-the pyramid may show peculiarities, for instance three may be large and
-three small, as in Fig. B, Plate 30, or the alternate ones may be duller
-or etched in some manner. The crystals are clear and when pure
-colorless, but there is a tendency for some slight impurity to color
-them almost any hue.
-
-The most perfect double-ended crystals form only where growth is
-possible in all directions, as in clay. In cavities and caves there is
-an opportunity for the crystals to grow in toward the open spaces, and
-in such places, one finds fine large crystals; the Alps, Brazil, Japan,
-and Madagascar being especially famous localities. The largest quartz
-crystal on record is one 25 feet in circumference which came from
-Madagascar. In this country the caves at Little Rock, Ark., have
-furnished some very fine large crystals. Smaller, but very clear
-crystals, come from about Herkimer, N. Y. Some of these have been used
-as “Rhine-stones” and as cheap imitations of diamonds. Clear quartz is
-beautiful enough to be a gem, but it is too common to interest people as
-jewelry, however many objects of art have been carved from it. One of
-these took the form of crystal balls, which, through the Middle Ages
-particularly, developed into a form of mysticism. The gazing into the
-crystal ball was supposed to give some people supernatural vision. It
-seems to be a form of hypnotism, gazing at the bright reflecting surface
-tiring the eye, and making possible visions, which are subjective rather
-than anything external.
-
-Silica is slightly soluble in water, especially when it is alkaline; so
-that most river-, lake-, and sea-waters have some silica in solution,
-and are carrying it from one place to another. The waters, which
-percolate through the rocks, carry even more, and when they come out
-into open spaces, they give up some of the silica, making crystals
-lining these openings, whether fissures or cavities. Not infrequently
-these silica-bearing waters dissolve out some other crystal, and then
-deposit in its place silica, thus making a crystal which has the form of
-what was dissolved, rather than that of quartz. Such a form is known as
-a pseudomorph.
-
-When molten masses of igneous rock were cooling the quartz crystals had
-their faces interfered with as they grew, and we have resulting
-crystalline quartz, simply filling in the spaces between the other
-crystals, such as feldspar and mica, in the granite. Quartz is a large
-component in many igneous rocks, also in metamorphic rocks, and certain
-sedimentary rocks like sandstone are almost wholly made up of quartz
-grains. Quartz is also the gangue mineral in many veins. In this case it
-seems to have been deposited from hot water or vapors, as they rose from
-cooling magmas. With it are associated all sorts of metallic ores as has
-been suggested.
-
-Quartz has been largely used to make imitations of other much rarer
-minerals, sometimes in its crystalline form to imitate the diamond, at
-other times ground and made into a “paste,” which is colored to imitate
-other gems. This paste is a mixture of about 4 parts of quartz, 5 parts
-of red lead and 1 part of potassium carbonate, melted and cooled slowly.
-It is clear and has a brilliant luster like the diamond. If some
-coloring matter is put into it it can be used for rubies, sapphires,
-etc. When there is any reason to think that this is being used, it is
-easily detected by being so much softer than any of the true gems, and
-even than true quartz. Quartz will scratch glass readily, but this
-imitation has only the hardness of very soft glass, or about 5.
-
-
-                          Varieties of Quartz
-
-Rock crystal is the term applied to quartz when it is clear and
-colorless.
-
-Milky quartz is the milky variety, the whiteness being due to
-imperfections in the crystallization, such as cracks, bubbles, etc.
-
-Smoky quartz is the cloudy brown-colored variety, which results from the
-presence of small quantities of organic matter (hydrocarbons) in the
-quartz. If the color is so dark as to be almost black it is termed
-morion. In the above cases the color will disappear if the stone is
-heated. Pebbles of smoky quartz from Cairngorm, Scotland, have been so
-widely used as semiprecious stones that they have come to be known as
-cairngorms.
-
-Citrine, or false topaz, is a clear yellow variety, the color again due
-to the presence of organic matter. It is distinguished from true topaz
-by the lesser hardness, this having the hardness of 7, while true topaz
-has a hardness of 8.
-
-Amethyst is quartz with a violet color, due to the presence of small
-quantities of manganese. To be suitable for cutting into gems, the color
-must be deep or the small pieces will appear almost colorless. It is
-widely used today as a semiprecious stone in jewelry; and in the
-fifteenth century it had the traditional virtue of making the wearer
-sober-minded, whether he had taken too freely of wine, or was over
-excited by love-passion.
-
-Rose quartz gets its pale-red color from the presence of a small amount
-of titanium. It is widely distributed, but is more abundant in the Black
-Hills of South Dakota.
-
-Aventurine is quartz which has inclosed tiny scales of mica or hematite
-giving it a spangled appearance.
-
-Prase is a green quartz, the color being due to the inclusion of fibrous
-crystals of green actinolite.
-
-Cat’s Eye is a quartz which has inclosed silky fibers of asbestos. When
-this is cut parallel to the fibers, the effect is opalescent. The colors
-are greenish, yellowish-gray, and brown. This form, however, is not to
-be confused with the true or Oriental Cat’s Eye, which is chrysoberyl
-and has the hardness of 8.
-
-
-Chalcedony
-SiO₂
-
-Non-crystalline, occurring in botryoidal, stalactitic or concretionary
-masses; hardness, 7; specific gravity, 2.65; color white when pure;
-luster waxy; translucent to transparent on thin edges.
-
-In addition to the crystalline form, silica is freely deposited in an
-amorphous or cryptocrystalline form which has the same properties as
-quartz, except the crystal faces. This is called chalcedony, and it
-occurs in seams, cavities and free surfaces. When the surface of a
-chalcedony deposit is free it has a waxy luster. It is generally very
-brittle and breaks in a peculiar splintery manner. Like quartz it also
-has a great many varieties, according to the impurities present. Its
-wide distribution, hardness, and the manner in which it can be chipped
-have made this a most important stone in the history of the development
-of civilization. The early men first broke it into rough tools, such as
-knives, axes, spear points, etc., and used these as cutting tools, of
-one sort or another, because they held their edge better than most
-stones. We apply, to the people who used only these chipped stones as
-tools, the term “_Men of the Old Stone Age_,” or the period is termed
-the _Palæolithic Age_. Later men learned how to grind the edge to a
-smoother outline, and this much shorter period is termed the _Neolithic
-Age_. The use of flints for the first tools is world-wide, and the
-American Indian when discovered was still using chalcedony in its
-rough-hewn state.
-
-      “There the ancient Arrow-maker
-  Made his arrow heads of sandstone,
-  Arrow heads of chalcedony,
-  Arrow heads of flint and jasper,
-  Smoothed and sharpened at the edges,
-  Hard and polished, keen and costly.”
-
-Chalcedony is the proper term to use when the color is white to
-translucent, in which case the surfaces are usually botryoidal and waxy.
-
-Carnelian is chalcedony which is clear red in color and translucent.
-This is one of the first stones used for ornamental purposes and for
-engraving. Carnelians with figures engraved on them were used by the
-Egyptians, Assyrians and The Children of Israel, at least 2000 B.C.; and
-the Egyptian scarabs of the fifth or sixth century B.C., were often
-carved from this variety of chalcedony, as well as from jasper and
-agates.
-
-The brownish varieties are termed _sard_.
-
-Chrysoprase is an apple-green variety of chalcedony the color being due
-to the presence of nickel oxide. This is by no means as common as most
-of the varieties of chalcedony, and was long prized as a gem.
-
-Plasma is chalcedony with a leek- to emerald-green color, and the same
-stone when it has small red spots of jasper in it is termed
-_blood-stone_, or _heliotrope_. These red spots are said by tradition to
-be drops of the blood of Christ.
-
-Jasper is a deep red chalcedony, the color being due to hematite, which
-is so abundant as to make it opaque. A brown variety colored by limonite
-is also called jasper, and even green jaspers are found. In all cases
-the opaque character is common.
-
-Flint is an impure brown chalcedony, usually forming concretions. The
-color is due to organic matter. Flint is mostly found in limestone or
-chalk, and the concretions are the result of the small particles of
-silica scattered through the rock being dissolved, and then
-reprecipitated about some organic center. Generally the silica was
-obtained by the dissolution of small fossils, like the shells of diatoms
-or sponge spicules.
-
-Hornstone and Chert are simply impure varieties of flint, brown in
-color, and with a splintery fracture.
-
-Agate, Plate 32, is a banded or cloudy chalcedony which has formed in a
-cavity, the layers of different color representing deposition from
-water, carrying first silica with one impurity, then later, silica with
-another impurity. Gradually the cavity has been thus filled with silica;
-and when the mass is freed by the weathering away of the surrounding
-rock, these banded masses are found. Sometimes the manner of deposition
-has changed, and while the outer part of the cavity was filled with
-chalcedony, the central part will contain quartz crystals. On account of
-the beauty of the colors, and the unusual way in which they may be
-developed, agates are widely used for semiprecious jewelry and objects
-of art, and this has been true since ancient times, the name itself
-coming from the River Achates in Sicily. The center for cutting and
-polishing agates is at Oberstein, Germany, where this work has been
-carried on since the middle of the fifteenth century. In spite of the
-many fine natural colors in agates, they are sometimes artificially
-colored, in many cases by methods which are kept as “trade secrets.” The
-color seldom penetrates far; so that even slight chipping reveals
-whether an inferior agate has been taken and colored up, or whether the
-stone is natural. Moss agates are chalcedony which has inclosed
-dendritic masses of some one of the manganese compounds as shown under
-manganite, p. 73.
-
-Onyx is a variety of agate where the bands are alternately black and
-white; while sardonyx is agate with red or brown bands alternating with
-the white. Such agates as these are especially desirable for cameo work,
-where the figure is carved in the chalcedony of one color, and the other
-color makes the background.
-
-Silicified or _agatized wood_ is a form of chalcedony, where silica has
-replaced wood, molecule by molecule; so that in good specimens, all the
-structure of the wood is still retained, and when thin sections are made
-it can be studied under the microscope almost as well as modern wood.
-This takes place under water, usually, if not always, in fresh water.
-Such fossilized wood is widely distributed in the western United States,
-the most famous cases being the Fossil Forest of Arizona, now a National
-Reservation, and the fossil trees in the Yellowstone National Park.
-
-
-Opal
-SiO₂·H₂O
-Pl. 33
-
-Non-crystalline, massive, stalactitic or nodular; hardness, 6; specific
-gravity 2; all colors; luster vitreous, resinous, or pearly; transparent
-on thin edges.
-
-Opal differs from chalcedony in having water, usually about 10%,
-incorporated in its structure. This is water of crystallization, and not
-firmly held; so that, if opal is heated in a closed tube to above 100
-C., it is given off as a vapor. Opal is distinguished from chalcedony by
-its lesser hardness, and the resinous to pearly luster. It forms in
-cavities, in layers often of extreme thinness.
-
-Opal is originally the product of the dissolution of silicate minerals
-in hot acid waters, the resulting gelatinous silica, when it is
-deposited and hardened, becoming the opal. There are many varieties,
-some of them highly prized as gems in spite of the moderate hardness and
-opacity of the mineral. Gem-quality opal gets its opalescent character
-from the successive deposition of thin films of opal, the light
-penetrating and being reflected from different films. This breaks up the
-white light and causes the play of colors which is the charm of this
-gem.
-
-Precious opal, in which the play of colors is finest, comes mostly from
-Hungary, Mexico, and Queensland. The opal was a favorite stone from
-before Roman times, and in its early history was a charm against the
-“evil eye.” During the nineteenth century for some reason it came to be
-considered an unlucky stone.
-
-Fire opal is a hyacinth-red to honey-yellow variety, which has a
-fire-like play of color, and is found in Mexico and Honduras.
-
-Common opal does not have the play of color, but comes in a variety of
-colors; is waxy or greasy in luster; and occurs mostly as fillings of
-seams or cavities, especially those in igneous rocks, like the steam
-holes in lavas, etc. It is found in Cornwall, Penn., in Colorado,
-California, etc.
-
-Opal-agate is a variety in which there are color bands, and it is widely
-distributed.
-
-Opalized wood is formed in exactly the same manner as agatized wood,
-much of the fossil wood called silicified being really opalized.
-
-Siliceous sinter is the porous mass of opal which is so frequently
-deposited about hot springs and geysers. It is readily recognized by its
-porous character.
-
-The shells of the diatoms, which are microscopic plants, are made of
-opal; and while they are so small, there is certainly no other plant so
-abundant or omnipresent, living as it does in every pool, lake, or sea
-by the millions. These shells are very indestructible so that they
-accumulate at the bottom of ponds, bogs, and sea-bottoms, making at
-times extensive deposits. This material in quantities is termed
-diatomaceous earth, or tripolite (from Tripoli where it was first used
-commercially). It is used as a polishing powder for metals, marble,
-glasses, etc.
-
-
-                             The Feldspars
-
-The term feldspar is a family name for a large variety of very common
-minerals, which altogether make up nearly 60% of the crust of the earth,
-being the predominant part of granites, gneisses, and lavas. In
-composition they are silicates of aluminum, together with potassium,
-sodium and calcium, and their mixtures. They may be tabulated as
-follows:
-
-  1. KAlSi₃O₈, _orthoclase_, the silicate of aluminum and potassium.
-  2. NaAlSi₃O₈, _albite_, the silicate of aluminum and sodium.
-  3. CaAlSi₂O₈, _anorthite_, the silicate of aluminum and calcium.
-  4. Mixtures of 1 and 2 are _alkalic feldspar_.
-  5. Mixtures of 2 and 3 are _plagioclase feldspar_.
-
-Orthoclase is monoclinic, but the rest of the feldspars are triclinic.
-If crystals are available they may be short and stout, or tabular and
-thin, but as the feldspars are mostly components of the igneous rocks,
-where perfect crystals have not had a chance to grow, they are mostly
-determined by their hardness and cleavage. The hardness of all the
-feldspars is 6 or very close to it.
-
-They all have three planes of cleavage, two of which are good and
-intersect either at 90° as in orthoclase, or at about 86° as in the
-plagioclase series; while the third cleavage plane is imperfect. In
-figure 1, Plate 34, a and b are the two perfect cleavages, while c is
-the imperfect one. Breaking into such cleavage masses as the one
-illustrated is characteristic of feldspar. The specific gravity ranges
-from 2.55 to 2.75. The luster is vitreous, and the color white, ranging
-to various shades of gray and pink, and, sometimes in recent lavas,
-colorless.
-
-Twinning is very common and helps to distinguish orthoclase from the
-plagioclase feldspars. In orthoclase the twins are simple, that is, only
-two crystals growing together, and are united on one of the faces, as if
-one of them had been revolved 180° with the other; or, while related to
-each other as in the preceding case, they may seem to grow through each
-other. On plate 34 are three orthoclase crystals showing this simple
-type of twinning. The first (A) is a simple crystal; the second (B)
-shows the simplest type of twinning where the left-hand crystal has
-revolved 180° on the p face, and the end is composed, half of the upper
-end of one crystal, and half of the lower end of the adjacent crystal.
-The presence of reëntrant angles calls attention to the twinning. The
-third figure (C) is a case of intergrowing crystals.
-
-In the plagioclase feldspars twinning is multiple, a large number of
-crystals, each thin, sometimes as thin as paper, growing side by side,
-the first one in normal position, the next at 180° with it, the third
-revolved 180° to the second and thus parallel to the first, and so on.
-The result is first of all a striated appearance, and second that, as
-plagioclase crystals have their prism faces intersecting at 86°, there
-is a series of low roofs and valleys, which are best seen by holding the
-piece of feldspar so the light reflects from a cleavage face, when it
-will appear striated; then by tilting it about 8 degrees a second set of
-reflections, also appearing striated, will appear. The light was first
-reflected from one side of the roofs, and in the second case from the
-other side. Figure D, Pl. 34, is a diagram showing the relation of the
-individual crystals in a multiple twinned piece of plagioclase, in which
-the crystals are represented as rather large. Plate 35, under
-labradorite, shows a photograph of a cleavage piece, on which is readily
-seen the striation which is characteristic of the plagioclase feldspars.
-
-Mixtures of albite and anorthite occur in bewildering numbers, one or
-the other predominating, and each mixture being uniform throughout the
-crystal and in the whole mass; so each combination is a mineral, each
-with its special properties; but the different plagioclase feldspars are
-so similar in appearance, that by the naked eye it is impossible to
-separate the closely related ones. This can be done under the microscope
-by studying the angles at which light is cut off, and also by chemical
-analyses. For our purposes six types will suffice to illustrate the
-group, and their composition may be indicated as follows.
-
-Albite is albite with up to 15% of anorthite mixed with it.
-
-Oligoclase is albite with from 15-25% of anorthite mixed with it.
-
-Andesite is albite with from 25-50% of anorthite mixed with it.
-
-Labradorite is anorthite with from 25-50% of albite mixed with it.
-
-Bytownite is anorthite with from 15-25% of albite mixed with it.
-
-Anorthite is anorthite with up to 15% of albite mixed with it.
-
-The best method for distinguishing these feldspars of the plagioclase
-group is to measure the angle between the two perfect cleavage faces,
-and even this requires careful measurement. The angles between these
-faces are as follows:
-
-               Orthoclase            90°
-               Microcline            89° 30′
-               Oligoclase            86° 32′
-               Andesite              86° 14′
-               Labradorite           86° 14′
-               Bytownite             86° 14′
-               Anorthite             86° 50′
-
-
-Orthoclase
-KAlSi₃O₈
-
-Occurs in granites, syenites, gneisses and light-colored lavas;
-hardness, 6; specific gravity, 2.57; color white to gray or pink;
-cleavage in two directions perfect and at 90°, in the third direction
-imperfect; luster vitreous; translucent on thin edges.
-
-Orthoclase is monoclinic, and when formed in cavities develops as
-crystals, but it is usually a constituent of igneous rocks, in which
-case the crystals have not had the opportunity to develop the crystal
-faces, and the orthoclase is in grains or irregular masses; and the best
-way of determining the mineral is the cleavage, the two perfect cleavage
-planes intersecting at right angles. Twinning is frequent but of the
-simple type, only two crystals being united, similar to either B or C on
-plate 34.
-
-It is found in granites, gneisses or lavas, wherever they occur, being
-especially characteristic of the granites of the Rocky Mountains.
-
-
-Microcline
-KAlSi₃O₈
-Pl. 35
-
-Occurs in granites and gneisses as crystals or irregular masses;
-hardness, 6; specific gravity, 2.56; color white to gray, pink, or
-greenish; luster vitreous; translucent on thin edges.
-
-Microcline has the same composition as orthoclase, but is in the
-triclinic system, the c axis being inclined a half degree away from a
-right angle with the b axis. This is best seen in the cleavage pieces,
-the two perfect cleavage planes meeting at 89° 30′, and this is the only
-test for determining this mineral by the unaided eye. Pike’s Peak is the
-best known locality for microcline, and there it occurs in fine large
-crystals of greenish color, which are known as _Amazon stone_.
-
-
-Albite
-NaAlSi₃O₈
-
-Occurs in small crystals, or more often in lamellar masses in granites
-or in seams in metamorphic rocks; hardness, 6; specific gravity, 2.62;
-color white to gray; luster vitreous.
-
-Albite may occur in simple crystals, in which case the two perfect
-cleavage planes meet at an angle of 86° 24′. However, it is much more
-frequently found twinned in the multiple manner, the individual crystals
-often being as thin as paper. This gives rise to a fine striation on the
-end of a crystal, or on the surface made by the imperfect cleavage
-plane. Where the crystals are extremely thin, the surface may have a
-pearly luster. Albite types of granite often inclose secondary minerals,
-that are prized as gems, such as topaz, tourmaline, and beryl.
-
-It is found at Paris, Me., Chesterfield, Mass., Acworth, N. H., Essex
-Co., N. Y., Unionville, Penn., and in Virginia, and throughout the Rocky
-Mountains.
-
-
-Oligoclase
-(NaCa)AlSi₃O₈
-
-Generally found in cleavable masses in granites and lavas, rarely in
-crystals; hardness, 6; specific gravity, 2.65; color white, greenish or
-pink; luster vitreous; translucent on thin edges.
-
-Oligoclase is a plagioclase feldspar and is distinguished by its two
-perfect cleavage planes meeting at an angle of 86° 32′, but otherwise it
-is very like albite. Crystals are not common, and it occurs mostly in
-masses, making one of the components of granite or lava.
-
-It is found in St. Lawrence Co., N. Y., Danbury and Haddam, Conn.,
-Chester, Mass., Unionville, Penn., Bakersville, N. C., etc.
-
-
-Labradorite
-(NaCa)AlSi₃O₈
-Pl. 35
-
-Usually found in cleavable masses in granites and lavas; hardness, 6;
-specific gravity, 2.71; color gray or white, often with a play of
-colors; luster vitreous; translucent on thin edges.
-
-Labradorite is distinguished by having the two perfect cleavage planes
-meet at 86° 14′. The iridescent play of color is also very
-characteristic and is generally present. It is due to the inclusion of
-minute impurities. This feldspar is usually associated with granites or
-lavas in which the dark minerals predominate. It gets its name from
-being the feldspar of the granites of Labrador, and is also found in the
-granites of the central part of the Adirondack Mountains and the Wichita
-Mountains of Arkansas.
-
-
-                              The Pyroxene Group
-
-The minerals of this group are generally associated with feldspars, and
-make the dark-colored component of granites, gneisses and lavas. This is
-especially true of those which have some iron in the crystal. Pyroxenes
-are salts of metasilicic acid (H₂SiO₃), in which the hydrogen (H) has
-been replaced by calcium, magnesium, iron, etc. The commoner minerals
-are orthorhombic or monoclinic, and all agree in their crystal habit,
-being short stout prisms, with the vertical edges so beveled that a
-cross section is eight-sided. The cleavage is good in two directions,
-parallel to the beveling faces (m in figure b, Plate 36), and they
-intersect at an angle of 87°. This is very characteristic, and if one
-has a crystal broken across, it is easy to see and measure this angle of
-intersection. These pyroxenes have the same chemical composition as the
-corresponding series of amphiboles, but the two are distinguished by
-several features. Pyroxenes are short and stout crystals, while
-amphiboles are long and either blade- or needle-like; pyroxenes are
-eight-sided in cross section, while amphiboles are six-sided; in
-pyroxenes the cleavage planes intersect at 87°, while in amphiboles they
-intersect at 55°. The minerals of this group are most frequently one of
-the components of a lava or granite, and are less frequently associated
-with metamorphic rocks. Three are common; enstatite, hypersthene, and
-augite.
-
-
-Enstatite
-MgSiO₃
-
-Usually occurs in lamellar or fibrous-lamellar masses in dark lavas;
-hardness, 5.5; specific gravity, 3.3; color gray, bronze or brown;
-luster vitreous, translucent on thin edges.
-
-Enstatite rarely occurs in crystals, but when it does they are
-orthorhombic. Usually it is in irregular masses with the cleavage
-angles, typical of pyroxene. The color is light, that is gray or
-brownish, and the streak white or nearly so. In most respects it is
-similar to hypersthene, which has the same composition, except that a
-large part of the magnesium is replaced by iron, and there are all sorts
-of gradations between the two minerals. When some iron takes the place
-of magnesium, the color darkens to, or towards bronze, until when about
-a third of the magnesium is so replaced, and the color is fully bronze,
-this variety is called _bronzite_. Bronzite is present in some of the
-dark lavas like gabbro and peridotite. Enstatite is found in the
-Adirondack Mountains, at Brewster and Edwards, N. Y., etc.
-
-
-Hypersthene
-(MgFe)SiO₃
-
-Occurs in cleavable masses in dark lavas; hardness, 5.5; specific
-gravity, 3.4; color dark-brown or greenish-brown; luster vitreous;
-translucent on thin edges.
-
-Hypersthene is a pyroxene in which magnesium and iron are present in
-about equal quantities. It is similar to enstatite, except that the
-color is darker, and the streak gray or brownish-gray in color. These
-two minerals grade into each other, so that there are cases where it is
-simply a matter of preference as to which name should be given to the
-mineral. This form is associated with dark lavas, of the gabbro or
-peridotite type, in such places as the Adirondack Mountains, Mount
-Shasta in California, Buffalo Peaks, Colo., etc.
-
-
-Augite
-CaMg(SiO₃)₂, MgAlSiO₆ + Fe₂O₃
-Pl. 36
-
-Usually occurs in short stout monoclinic crystals; hardness, 5.5;
-specific gravity, 3.3; color dark-green to black; luster vitreous;
-translucent on thin edges.
-
-Augite is a complex pyroxene having some iron and aluminum always
-present in it, but the amount not a fixed quantity. It is by far the
-commonest of the pyroxenes and has a wide distribution, both in the
-sorts of lavas in which it appears, and in the world. It is commonly the
-dark component of such lavas, as gabbros and peridotites, and also is
-common in metamorphic rocks, especially impure crystalline limestones.
-It is found at Raymond and Mumford, Me., Thetford, Vt., Canaan, Conn.,
-in Westchester, Orange, Lewis and St. Lawrence Counties of N. Y., in
-Chester Co., Penn., at Ducktown, Tenn., Templeton, Canada, etc.
-
-
-                             The Amphibole Group
-
-The amphiboles are a group of minerals made up of the same chemical
-elements as the pyroxenes, but with the molecular arrangement different,
-which appears in the forms of the crystals. The commoner ones are all
-monoclinic but contrast with the pyroxenes as follows. Amphiboles are
-long and slender crystals, while pyroxenes are short and stout;
-amphiboles are six-sided, while pyroxenes are eight-sided; amphiboles
-have the two perfect cleavages intersecting at 55° and 125°, while those
-of pyroxene intersect at 87° and 93°. With the above in mind it is easy
-to place the minerals in their proper group, but inside the group it is
-not always so easy to distinguish one from another. This group is
-associated rather with metamorphic rocks than with igneous rocks, with
-which the pyroxenes are mostly associated. The three commoner minerals
-of the group are tremolite, actinolite, and hornblende.
-
-
-Tremolite
-(CaMg)₃(SiO₃)₄
-Pl. 37
-
-Occurs in long prismatic crystals or in columnar or fibrous masses;
-hardness 5.5; specific gravity, 3; color white to gray; luster vitreous;
-transparent on thin edges.
-
-The long prismatic crystals of tremolite occur especially where
-dolomitic limestones have been altered by metamorphism. Sometimes these
-crystals grow side by side, making fibrous masses, where the long
-slender crystals can be picked apart with the fingers, and yet are
-flexible, and tough enough so that they can be felted together. This is
-termed asbestos, which, because it is infusible and a poor conductor of
-heat, is much used to make insulators, fire-proof shingles, and all
-sorts of fireproof materials. The varieties in which the crystals are
-finer and silky in appearance, like the one illustrated on Plate 38 are
-termed _amianthus_. There are other minerals, such as actinolite and
-serpentine, which occur in the same manner, and are also called
-asbestos, the serpentine variety being just now the most important
-commercially.
-
-Tremolite is found at Lee, Mass., Canaan, Conn., Byram, N. J., in
-Georgia, etc.
-
-
-Actinolite
-(CaMgFe)₃(SiO₃)₄
-
-Occurs in radiating crystals, or in fibrous masses; hardness, 5.5;
-specific gravity 3; color pale- to dark-green; luster vitreous;
-translucent on thin edges.
-
-Except for its green color, this mineral is very like tremolite. The
-difference between the two is due to the small amount of iron in the
-actinolite. It is usually found in schists, and the radiating character
-of the crystal groups is enough to determine the mineral, if it is
-already clear that it is one of the amphiboles. Occasionally it occurs
-with the crystals parallel to each other, making one of the forms of
-asbestos.
-
-Actinolite is found at Warwick, Edenville, and Amity in Orange Co., N.
-Y., at Franklin and Newton, N. J., Mineral Hill and Unionville, Penn.,
-Bare Hills, Md., Willis Mt., Va., etc.
-
-
-Hornblende
-(CaMgFe)₃(SiO₃)₄CaMgAl₂(SiO₄)₃
-Pl. 37
-
-Occurs in well-defined crystals, in grains and in masses; hardness, 5.5;
-specific gravity 3.2; color black, dark-green, or dark-brown; luster
-vitreous; translucent on thin edges.
-
-In composition hornblende corresponds to augite, but occurs in long
-slender, six-sided crystals with cleavage planes intersecting at 55°, so
-that it is a typical amphibole. It occurs in a very wide range of rocks,
-such as granite, syenite, diabase, and gabbro; and in such metamorphic
-rocks as schists and gneisses; and sometimes igneous rocks are made up
-almost entirely of hornblende, when they are known as amphibolites or
-hornblendite. It is found all through the New England States, down along
-the Piedmont Plateau, through the Blue Ridge Mountains, and in many of
-the western mountainous areas.
-
-
-                               The Garnet Group
-
-The garnets are a series of double silicates, which occur with
-surprisingly uniform characters. They are all isometric, and occur
-either as dodecahedrons, or as the 24-sided figure (the trapezohedron),
-which is formed by the beveling of the edges of the dodecahedron, and
-developing these new faces to the exclusion of the dodecahedron faces.
-Combinations of the dodecahedron and trapezohedron (36 faces) may occur.
-All the garnets have a hardness of 7 to 7.5, and the specific gravity
-runs from 3.2 to 4.3, according to the composition. In size they run
-from as small as a grain of sand up to as large as a boy’s marble, and
-occasionally even to four inches in diameter. The color varies with the
-composition, from colorless to yellow, red, violet, or green. There is
-no cleavage, and the luster is always vitreous.
-
-Garnets are usually accessory minerals, found in metamorphic rocks,
-though they are sometimes also present in granites and lavas. They are
-always segregations which have taken place in the presence of high
-temperatures. When clear and perfect several of the garnets are used as
-gems. On the other hand some of the common garnets occur in such
-quantities that they are crushed and used as abrasives, for such work as
-dental polishes, or for leather and wood polishing.
-
-The following is the composition of some of the commoner garnets.
-
-  Ca₃Al₂(SiO₄)₃    = grossularite
-  Mg₃Al₂(SiO₄)₃    = pyrope
-  Fe₃Al₂(SiO₄)₃    = almandite
-  Mn₃Al₂(SiO₄)₃    = spessartite
-  Ca₃Fe₂(SiO₄)₃    = andradite
-  Ca₃Cr₂(SiO₄)₃    = uvarovite
-
-Grossularite is chiefly found in crystalline limestones, which have
-resulted either from contact with lavas, or from general metamorphism of
-impure limestones. These garnets are colorless to white, or more often
-shades of yellow, orange, pink, green or brown, according to traces of
-impurity which they may contain. The cinnamon-colored variety from
-Ceylon is termed _cinnamon stone_, and is a fairly popular gem.
-
-Pyrope is a deep-red color and when perfect is highly prized as a gem.
-It is found in dark-colored igneous rocks, like lavas, or serpentines.
-Some of the finest come from South Africa, where they are found in
-company with the diamond.
-
-Almandite is dark-red to brown in color, the brownish-cast
-distinguishing it from pyrope. It is one of the garnets known as “common
-garnet.” In some cases it is clear and deep colored enough to be used as
-a gem, but mostly it is muddy in appearance. The name almandite comes
-from Alabanda, a city of the ancient district of Caria, Asia Minor,
-whence garnets were traded to ancient Rome. The finest garnets “Sirian
-garnets” came from the city of “Sirian” in Lower Burma, and were
-supposed to have been found near there, but careful investigation shows
-that no garnets occurred near there, and this town was therefore, even
-at that early time, a distributing point for garnets, found probably
-further to the east. The “Sirian” garnet had a violet cast and now the
-term is used to indicate a type of garnet, rather than a locality.
-
-Spessartite is dark-hyacinth-red, or red with a violet-tinge, and is one
-of the less-common garnets. It is usually found in granites. The finest
-garnets of the type come from Amelia Court House, Va., which has yielded
-some ranging from one up to a hundred carats.
-
-Andradite is another garnet which is termed “common garnet.” It is red
-in color, but with a yellowish-cast which distinguishes it from
-almandite, but these two are not easy to separate. It is found mostly in
-metamorphosed limestones. One variety is black in color and called
-_malanite_. It is found in lavas. The common yellowish-red garnets are
-found through New England and the Piedmont Plateau.
-
-Uvarovite is a rare garnet of emerald-green color, found in association
-with chromium ores.
-
-The number of localities for garnets is so great that a list would
-suggest most of the regions where metamorphic rocks occur, as all over
-New England, throughout the Piedmont Plateau, the Rocky Mountains, etc.
-Certain fine clear garnets, found in Montana, northeastern Arizona, and
-northwestern New Mexico are sold under the trade name of “Montana,
-Arizona or New Mexico rubies.” These are of fine quality and are mostly
-collected by the Indians from the ant hills and scorpion’s nests of
-those regions.
-
-Garnets are among the earliest stones mentioned in ancient languages, as
-would be expected from the way these hard and beautiful crystals weather
-out of the much softer metamorphic rocks, like schists. In the past
-they, with most any other translucent red stone, were included under the
-name _carbuncle_. This, however, is not the name of any mineral, but
-refers rather to a mode of cutting, _en cabochon_ or with a convex
-surface.
-
-
-                                Glucinum
-
-Glucinum is a rare metal, silvery-white in color, malleable, and melting
-at a fairly low temperature. It is found in the mineral beryl, from
-which has come the alternative name _beryllium_. The name comes from the
-sweet taste of its salts. Except for beryl its minerals are rare, and
-the metal has found but few uses for man.
-
-
-Beryl
-Gl₃Al₂(SiO₃)₆
-Pl. 39
-
-Occurs in hexagonal crystals in granites, gneisses and mica schists;
-hardness, 7.5; specific gravity, 2.7; color usually some tint of green;
-luster vitreous; transparent on thin edges.
-
-When this mineral occurs in coarse hexagonal prisms, with or without
-faces on the ends, it is known as beryl; when the crystals are clear and
-perfect and of a dark-green color, they are of gem value and are termed
-_emerald_; when of a light-green color, they are _aquamarine_; and when
-bright-yellow in color, they are the _golden beryl_. There is little
-difficulty in determining beryl, for only apatite occurs in such
-crystals, and is green, and this latter mineral has a hardness of only
-5. There is an imperfect basal cleavage.
-
-Ordinary beryl is fairly common in granites of the pegmatite sort, and
-less common in gneisses and mica-schists. This type often furnishes
-crystals of large size, up to two and three feet in diameter.
-
-Beryl which is free from cracks and inclosures, so it can be used as a
-gem, is so rare, that the emerald has a value above that of the diamond,
-and second only to the ruby. It is one of the gems with a long history,
-having been quarried on the west coast of the Red Sea at least 1650 B.C.
-by the Egyptians. To early people it had a power to quicken the prophet
-instinct and made the wearer see more clearly. The Spanish
-conquistadores found fine emeralds among the treasures of both Mexico
-and Peru. In the United States, Stony Point, N. C., was a notable
-locality for these gems, but now seems to have been exhausted. The name
-emerald has been applied to many other green stones, usually with some
-geographical modification, as “Oriental emerald” which is green
-corundum, “Brazilian emerald” which is tourmaline, etc.
-
-Giant beryls have been found at Acworth and Grafton, N. H., and at
-Royalston, Mass. Localities for ordinary beryl are Albany, Norway,
-Bethel, Hebron, Paris, and Topsham, Me., Barre, Goshen and Chesterfield,
-Mass., New Milford and Branchville, Conn., Chester and Mineral Hill,
-Penn., Stony Point, N. C., and many other localities in the
-Appalachians; also Mount Antero, Colo., and in the Black Hills of South
-Dakota.
-
-
-Sodalite
-Na₄Al₃Cl(SiO₄)₃
-
-Occurs in irregular masses, sometimes in dodecahedrons; hardness, 5.5-6;
-specific gravity, 2.3; color deep-blue to colorless; streak white;
-luster vitreous; translucent on thin edges.
-
-This striking mineral, with its deep-blue to azure color, is not easily
-confused with any other. It is characteristic of soda-rich igneous rocks
-such as syenite and some lavas. In this country it is found at
-Litchfield, Me., and Salem, Mass.
-
-
-Zircon
-ZrSiO₄
-Pl. 39
-
-Usually occurs in tetrahedral crystals in igneous rocks; hardness, 7.5;
-specific gravity, 4.7; color brown; luster vitreous; translucent on thin
-edges.
-
-Zircon, the mineral of the rare earth element zirconium, nearly always
-occurs in light-colored igneous rocks, like syenite. It may occur in
-schists or gneisses, but in these rocks the crystals are of microscopic
-size. Because of their great hardness and insolubility, zircon crystals
-resist weathering and are often found, along with gold, cassiterite, or
-magnetite, in sands which have resulted from the disintegration of
-syenite rocks.
-
-Zircon refracts and disperses light to a degree second only to the
-diamond, so that clear crystals are sought as gems. They are often
-called “Matura diamonds” because of their abundance at Matura, Ceylon.
-When the crystals are colorless or smoky they are termed _jargons_ or
-_jargoons_; when of a red-orange hue, they are _hyacinth_ or _jacinth_.
-Most of the zircon of gem-quality comes from Ceylon, where it is picked
-up as rolled-pebbles from the beds of brooks.
-
-The most remarkable American locality for zircon is near Green River, in
-Henderson Co., N. C., where it is found abundantly in a decomposed
-pegmatite dike, from which many tons have been obtained. It is also
-found at Moriah, Warwick, Amity and Diana, N. Y., at Franklin Furnace,
-and Trenton, N. J., in the gold-bearing sands of California, etc.
-
-
-Cyanite
-Al₂SiO₅
-Pl. 40
-
-Occurs in long blade-like crystals in gneisses and schists; hardness, 7
-at right angles to the length, and 4.5 parallel to the length; specific
-gravity, 3.6; color blue; luster vitreous; translucent on thin edges.
-
-There are only a few blue minerals, and the way in which cyanite occurs
-in long thin blade-like crystals is entirely characteristic. If more is
-still wanted to determine this mineral, its unique character in having
-the great hardness 7 when scratched parallel to the length, and only 4.5
-when scratched crossways, will settle any doubts.
-
-The mineral _sillimanite_ has the same composition as cyanite, but is
-fibrous in habit and has the hardness 6.5. If cyanite is heated to 1350°
-C. it changes its character and becomes sillimanite.
-
-Cyanite is found as an accessory mineral in metamorphic rocks, such as
-gneiss and schist, at Chesterfield, Mass., Litchfield and Oxford, Conn.,
-in Chester Co., Penn., in North Carolina, etc.
-
-
-                                The Mica Group
-
-The micas are very common minerals, easily recognized by their very
-perfect basal cleavage, as a result of which thin sheets, often less
-than a thousandth of an inch in thickness, readily split off. These are
-tough and elastic, which distinguishes mica from the chlorite group in
-which there is similar basal cleavage, but the sheets are not elastic.
-
-Micas are complex silicates of aluminum, with potassium, iron, lithium,
-magnesium and hydrogen. They are one of the principle components of many
-granites, gneisses, and schists. This mineral is always crystalline,
-being in the monoclinic system, but occurring in six-sided prisms. The
-cleavage is so dominant a character that the crystal form is usually
-overlooked, as it is seldom requisite in determining this mineral. The
-size of the sheets of mica depend on the size of the crystals, the
-larger sheets expressing great slowness in cooling from the original
-magmas. Sometimes the crystals may be two or even three feet in
-diameter. The hardness is not great, ranging between 2 and 3. The
-specific gravity lies between 2.7 and 3.2. The color varies according to
-the composition, from silvery-white, through gray, pink, and green to
-black. The luster is vitreous to pearly, sometimes gleaming in the
-darker-colored varieties. The commoner types of mica are as follows:
-
-  Muscovite, H₂KAl₃(SiO₄)₃ or potash mica.
-  Lepidolite, LiK(Al₂OH·F)Al(SiO₃)₃ or lithia mica.
-  Biotite, (HK)₂(MgFe)₂Al₂(SiO₄)₃ or iron mica.
-  Phlogopite, H₂KMg₃Al(SiO₈)₃ or magnesia mica.
-
-Muscovite is colorless, silvery-white, gray or sometimes pale-green or
-brown. It gets its name from Moscow where it was early used for window
-panes, and it is still used for stove and furnace doors, as well as in
-electric work, for a lubricant, etc.
-
-The best crystals occur in granites, in the coarse varieties of which
-large crystals may be obtained. It is found also as small scales in
-gneisses and schists, and when weathered from its original rocks it may
-be present in sandstones and shales. Muscovite is always in its origin
-an elementary component of deep-seated igneous rocks, like granite; but
-is never a component of extruded lavas. _Sericite_ is muscovite which
-has been secondarily produced by the alteration of other minerals into
-muscovite, as when feldspar, cyanite, topaz, etc., have been modified by
-the presence of heat and hot vapors, when near lavas that have come in
-contact with other rocks. Muscovite is very resistant to alteration by
-weathering, but when it does change, the greater part of it becomes
-kaolin. It is found at Acworth and Grafton, N. H., in plates, sometimes
-a yard across at Paris, Me., Chesterfield and Goshen, Mass., Portland
-and Middletown, Conn., at Warwick, Edenville, etc., N. Y., and all down
-the Appalachian Mts., also in the Rocky Mts., the Cascade Range, etc.
-
-Lepidolite is pink or lilac in color and occurs in scaly masses, mostly
-in granites. It does not come in large crystals. Lepidolite is found at
-Paris and Hebron, Me., Middletown, Conn., Pala, Calif., etc.
-
-Biotite is dark-brown or black mica. Like muscovite it is very common,
-making one of the chief components of granites, gneisses and schists;
-and, unlike muscovite, it may occur in extrusive lavas, like trachyte,
-andesite, and basalt. It resists weathering much less than muscovite, so
-that, when the rocks of which it is a component disintegrate, biotite is
-usually altered to kaolin and other compounds. It is likely to occur in
-good-sized crystals, especially at Topsam, Me., Moriah, N. Y., Easton,
-Penn., etc.
-
-Phlogopite is pale-brown, often coppery in color, and is most likely to
-occur in serpentines, or crystalline limestones or dolomites, often in
-fine crystals, of good size. While one of the less abundant micas, this
-is found at Gouverneur, Edwards, and Warwick, N. Y., Newton, N. J., and
-Burgess, Canada.
-
-
-Topaz
-Al₂F₂SiO₄
-Pl. 41
-
-Occurs in crystals mostly; hardness, 8; specific gravity, 3.5; colorless
-to pale-yellow; luster vitreous; transparent on thin edges.
-
-Topaz may be colorless, but is more often some shade of yellow, and at
-times brown or even blue. Its hardness is characteristic, there being
-but few minerals as hard, and it is used to represent the hardness 8 in
-the Moh’s scale. The crystals are orthorhombic prisms, with the edges of
-the prism beveled and often striated. The ends of crystals usually
-terminate with a basal plane, parallel to which there is good cleavage.
-Between this basal plane and the prism faces there are usually several
-sets of small faces as indicated on Plate 41.
-
-This mineral, as is also true of most minerals containing fluorine, is
-one of those which have crystallized out from hot vapors, escaping from
-igneous magmas. It is associated with such minerals, as tourmaline,
-beryl, fluorite, and cassiterite, and occurs mostly in cavities or
-seams, in or near granites.
-
-Ordinary topaz, which means crystals that are imperfect by reason of
-tiny cracks and impurities is not very rare, but crystals which are
-perfect and clear in color are considered gems. Most of the gem-topaz is
-some shade of yellow, but may be brown or blue, never, however, pink, as
-is often seen in jewelry. The “pinking” is artificial, and done by
-packing yellow or brown topaz in magnesia, asbestos, or lime, and then
-heating it slowly to red heat, after which it is cooled slowly. If
-underheated the color is salmon, if overheated all color disappears.
-Topaz has been a gem for centuries, the earliest records coming from
-Egypt. The name comes from _topazios_, meaning to seek, because the
-earliest known locality, from which it was gathered, was a little island
-of that name in the Red Sea, and this island was often surrounded by fog
-and hard for those early mariners to find. Here by mandate of the
-Egyptian kings the inhabitants had to collect topazes, and deliver them
-to the gem-cutters of Egypt for polishing.
-
-Several yellow stones are called topaz, as the “Oriental topaz” which is
-corundum and more valuable than topaz itself; and several varieties of
-yellow quartz, which go under such names as “Saxon,” “Scotch,”
-“Spanish,” and “smoky” topaz. When topaz occurs colorless as in Siberia,
-the Ural Mountains, and in the state of Minas Geraes, Brazil, in all of
-which places it is found as pebbles in brooks, it goes under the name of
-“slave’s diamonds.” Brazil is today the chief source of gem-quality
-topaz.
-
-Ordinary topaz is found in this country at Trumbull, Conn., Crowder’s
-Mt., N. C., Thomas Mts., Utah, in Colorado, Missouri, and California,
-etc.
-
-
-Staurolite
-FeAl₅OH(SiO₆)₂
-Pl. 41
-
-Occurs in orthorhombic crystals; hardness, 7.5; specific gravity, 3.7;
-color brown; luster resinous; translucent on thin edges.
-
-This mineral occurs about equally abundantly in simple crystals similar
-to the outline on Plate 41, and in twins which have grown through each
-other either at 90° or at 60°. The color is either brown or
-reddish-brown. In all cases it is an accessory mineral, occurring in
-metamorphic rocks, usually schists, though less frequently in slates and
-gneisses.
-
-From the seventeenth century on, it has been used as a baptismal stone,
-and worn as a charm, legends stating that it fell from the heavens. Fine
-crystals have been found in Patrick County, Va., and there is in this
-region the legend, that when the fairies heard of the crucifixion of
-Christ, they wept and their tears falling crystallized in the form of
-crosses, such as the one shown on Plate 41.
-
-Staurolite is found in the schists of New England as at Windham, Me., or
-Chesterfield, Mass., and all down the east side of the Appalachian
-Mountains to Georgia.
-
-
-Olivine
-(MgFe)₂SiO₄
-_Peridot_ or _Chrysolite_
-
-Occurs in grains and irregular masses in dark lavas; hardness 6.5 to 7;
-specific gravity 3.3; color bottle- to olive-green; luster vitreous;
-translucent on thin edges.
-
-Olivine rarely occurs in crystals, but when it does they belong to the
-orthorhombic system. The dark-green grains or masses are recognized by
-the color, considerable hardness and indistinct cleavage. Serpentine may
-have a similar color, but its hardness is only 4. In hydrochloric acid
-olivine decomposes to a gelatinous mass.
-
-Olivine is typically one of the constituents of the dark lavas, like
-basalt, gabbro, or peridotite. It is also a common mineral in
-meteorites. Olivine, in the presence of water, alters to other minerals,
-especially serpentine, with great facility.
-
-It occurs fairly widely wherever the dark lavas are present, as in the
-White Mountains of N. H., in Loudoun Co., Va., in Lancaster Co., Penn.,
-and in many localities in the Rocky Mountains and Cascade Range.
-
-
-Epidote
-Ca₂(AlOH)(AlFe₂)(SiO₄)₃
-Pl. 42
-
-Occurs in grains or columnar masses; hardness, 6.5; specific gravity
-3.4; color green, usually a pistachio or yellow-green; luster vitreous;
-translucent on thin edges.
-
-Rarely epidote occurs in crystals, which belong to the monoclinic
-system, and may be either short like the diagrams on plate 42 or long
-and needle-like. The color and hardness will suffice to determine this
-mineral, as almost no other has the peculiar yellowish-green color which
-is characteristic of this form.
-
-Epidote occurs primarily in metamorphic rocks at or near the contact
-with igneous rocks; or it may be a secondary mineral resulting from the
-weathering of granites, especially along seams. It sometimes occurs with
-hornblende in highly folded schists, as in New York City. It is often a
-mineral which has resulted from the alteration of other minerals, as
-pyroxene, amphibole, biotite, or even feldspars.
-
-It is found at Chester and Athol, Mass., Haddam, Conn., Amity, Munroe
-and Warwick, N.Y., East Branch, Penn., in the Lake Superior region, in
-the Rocky Mountains, etc.
-
-
-Tourmaline
-(FeCrNaKLi)₄Mg₁₂B₆Al₁₆H₈Si₁₂O₆₃
-Pl. 42 & frontispiece
-
-Occurs in three-sided prismatic crystals; hardness, 7; specific gravity,
-3.1; colorless, red, green, brown, or black; luster vitreous;
-transparent on thin edges.
-
-Tourmaline is readily distinguished from other minerals, as it always
-occurs in long to short prisms, which are three-sided in cross section.
-There is also a tendency for the sides to be curved as seen on the end
-view of D, Pl. 42. Frequently the vertical edges of the prism are
-beveled with one, two or three faces, grouped about each of the three
-original edges, and there are often striations on the prism faces. The
-ends are terminated by a low rhombohedron and again there may be a host
-of modifying faces on the edges and corners of the end. The common
-varieties are brown or black in color, but occasionally there may occur
-green, red, yellow or almost any color. When the crystals are perfect,
-that is free from impurities and without tiny cracks, tourmaline becomes
-a gem of popularity and value.
-
-Tourmaline is very complex in composition and may vary considerably, the
-sodium, potassium, lithium, magnesium, and iron being either more or
-less abundant or even lacking. The color is to some extent dependent on
-the proportions of these elements present, the dark varieties having
-more iron, and the light colored tourmalines lacking it. This mineral is
-one of those which form from superheated vapors, escaping from molten
-magmas. It will therefore occur in veins, often associated with copper
-minerals, in crystalline limestones, or in cavities in granites, where
-it is associated with such minerals, as beryl, apatite, fluorite, topaz,
-etc.
-
-If heated tourmaline crystals develop electricity, with the effect of
-making one end a positive and the other a negative pole, and then will
-attract bits of straw, ashes, etc. It was first introduced into Europe
-about 1703 from India, and its vogue as a gem has greatly increased
-since it was found on Mount Mica near Paris, Me. This Paris, Me.,
-locality was discovered by two boys, amateur mineralogists, Elijah L.
-Hamlin and Ezekiel Holmes, who in 1820 were returning home from a trip
-hunting for minerals, when, at the root of a tree, they discovered some
-gleaming green substance. It proved to be gem-quality tourmaline. A snow
-storm that night buried their “claim,” but next spring it was visited
-and several fine crystals found. Later this locality was systematically
-worked, and over $50,000 worth of tourmaline taken from the pegmatite
-seam in the granite, which lay under the crystals found on the surface.
-The figure in the frontispiece is one of the crystals from there.
-
-Well known localities are Paris and Hebron, Me., Goshen and
-Chesterfield, Mass., Acworth and Grafton, N. H., Haddam and Munroe,
-Conn., Edenville and Port Henry, N. Y., Jefferson Co., Colo., San Diego
-Co., Calif., etc.
-
-
-Kaolinite
-H₄Al₂Si₂O₉
-_Kaolin_
-
-Usually found in whitish clay-like masses; hardness, 2; specific
-gravity, 2.6; color white to grayish or yellowish; luster dull.
-
-Kaolinite does not generally occur in crystals, though crystals of
-microscopic size and monoclinic forms have been found. It is a secondary
-mineral resulting from the decomposition by weathering of feldspars, the
-calcium, potassium or sodium having been replaced by water. When found
-in place it is generally white or nearly white, and is characterized by
-its greasy feel.
-
-As granites or other feldspar-bearing rocks are weathered away, the
-kaolin is washed out by water, and with other fine material is carried
-down into lakes or the sea, where it settles to the bottom and is known
-as clay. Clay is kaolin with more or less impurities.
-
-Pure kaolin is used for the manufacture of china and white porcelain
-ware; but when it is impure, especially when it has iron in it, baking
-causes the product to turn red or brown, so that it is only suitable for
-making tile, bricks, etc.
-
-It is found almost anywhere that feldspar rocks are, or have been,
-exposed to weathering.
-
-
-Talc
-H₂Mg₃(SiO₃)₄
-
-Occurs in scales, or in fibrous, scaly or compact masses; hardness, 1;
-specific gravity, 2.7; color white, gray or pale-green; luster pearly;
-translucent on thin edges.
-
-This mineral is as soft as any, only graphite and molybdenite being of
-the same hardness, but both these latter two have a black streak, while
-the streak of talc is white. The greasy feel is also characteristic.
-Talc is very seldom found in crystals, but if they are found, they will
-appear like flakes and have a hexagonal cross section, though in reality
-they belong to the monoclinic system.
-
-Talc is a secondary mineral which usually results from the exposure of
-magnesium silicates, such as pyroxenes or amphiboles, to moisture. In
-this case, in-as-much as the original rocks were metamorphic in origin,
-the talc therefrom will occur in old metamorphic regions. Some talc is
-also formed by the action of silica-bearing waters on dolomite. This is
-likely to be the case near the contact between dolomite and igneous
-rocks. Talc is closely related to serpentine and likely to be found in
-the same regions.
-
-Talc has come to have a considerable use. Some of it is compact and then
-called soapstone, and this was used by the ancient Chinese to make
-images and ornaments; and our North American Indians used it to make
-large pots, to serve as containers for liquids. Some of these pots have
-been carved out with great skill, so as to be fairly light in proportion
-to what they would hold. Pipes and images were also carved from
-soapstone. Today we still cut soapstone into slabs to make mantels,
-laundry tubs and sinks. The scaly and fibrous varieties are ground, and
-used in making paper, paint, roofing, rubber, soap, crayons, toilet
-powders, etc. The United States produce and use over half the world’s
-production, our industries requiring over 100,000 tons of talc a year.
-Of this 38% goes into paper, 23% into paint, 18% into roofing, and so on
-down to toilet powder which uses 2½%, or 2,500 tons a year.
-
-Talc is found in metamorphosed regions, that is in New England, all down
-the east side of the Appalachian Mts., in the Rocky Mts., and the
-Cascade Ranges, with a large number of local occurrences. New York State
-is the leading producer.
-
-
-Serpentine
-H₄Mg₃Si₂O₉
-Pl. 43
-
-Occurs in compact, granular or fibrous masses; hardness, 3; specific
-gravity, 2.6; color green; luster greasy; translucent on thin edges.
-Serpentine is never in crystals. Its color and hardness serve to
-distinguish it. Like talc it is a secondary mineral resulting from the
-alteration, in the presence of moisture, of pyroxenes, amphiboles, and
-especially, olivine. As these are often in metamorphic rocks, the
-serpentine is likely to be associated with metamorphic rocks. Some
-serpentine is also the result of the action of silica-bearing water on
-dolomite, and this is likely to occur in areas of sedimentary rocks. The
-fibrous variety of serpentine, _chrysolite_, usually occurs in seams or
-veins, and when the fibers are long, it is used as asbestos. This form
-of asbestos is the one most used commercially today, as there are
-remarkably large deposits of it in the Province of Quebec, which provide
-the major part of the world supply. In the United States it is also
-found in California and Arizona but only in moderate quantities.
-
-Massive serpentine is used in considerable quantities as an ornamental
-stone, the green color varied with streaks and blotches of white, yellow
-and red, due to various impurities, making it very effective. It is,
-however, only suitable for interior work as the weather quickly spoils
-the polished surface. This is further discussed under serpentine rock,
-page 245.
-
-Serpentine is found at Newfane, Vt., Newburyport, Mass., Brewster,
-Antwerp, etc., N. Y., Hoboken, N. J., in Pennsylvania, Maryland, etc.
-
-
-Chlorite
-H₈(MgFe)₅Al₂(SiO₆)₃
-Pl. 43
-
-Occurs in monoclinic crystals of six-sided outline, or in scaly flakes
-or masses; hardness, 2; specific gravity 2.8; color green; luster pearly
-on cleavage faces; translucent on thin edges.
-
-Chlorite is a family name, covering a series of closely related
-minerals, so similar in appearance that they are best considered under
-this common name. In many respects they resemble mica, in the shape of
-the crystals and the remarkable basal cleavage. At first glance it is
-easy to confuse the two, but chlorite scales are not elastic, and when
-bent, stay bent, instead of snapping back like mica. In fact they look
-like more or less rotted micas. This is more than appearance, for
-chlorites form as a result of the alteration of micas in the presence of
-moisture. They are then secondary, and will be found where mica-rocks
-have been weathered, as in granites and schists.
-
-They may be expected anywhere that micas have been long exposed, as in
-New England, the Rocky Mountains, or the Sierra Nevada or Cascade
-Ranges. Special localities are Brewster, N. Y., Unionville and Texas,
-Penn., etc.
-
-
-                              The Zeolites
-
-The zeolites are a group of white minerals, with a pearly luster, light
-weight, and easy solubility in acids; which, because their contained
-water is lightly held, readily boil before the blowpipe. They are all
-secondary minerals, which result from the decomposition of feldspars,
-when exposed to weathering. They are almost universally found in seams
-and cavities of disintegrating lavas. From a group of a dozen or so,
-three are common enough to be considered here. They may be found by
-watching such places, as where trap rock is being quarried for road
-material, or being blasted for any reason.
-
-
-Analcite
-Na₃Al₂Si₄O₁₃ + 2H₂O
-Pl. 44
-
-Occurs as trapezohedrons in seams and cavities in lavas; hardness, 5.5;
-specific gravity, 2.2; colorless, white or pink; luster vitreous;
-transparent on thin edges.
-
-Analcite usually occurs in the 24-sided form, known as a trapezohedron,
-as illustrated in figure A, Pl. 44; but it may also occur in cubes with
-the three faces of the trapezohedron on each corner. Small crystals are
-often colorless, but the larger ones are either white or pink, and are
-opaque. While the form is the same as that of garnets, the color, lesser
-hardness, and the occurrence in lavas will serve to distinguish this
-mineral. If placed in hydrochloric acid analcite dissolves to a
-gelatinous mass.
-
-It is always found in seams and cavities in lavas, as at Bergen Hill and
-Weehawken, N. J., Westfield, Mass., in the Lake Superior region, etc.
-
-
-Natrolite
-Na₂Al₂Si₃O₁₀ + 2H₂O
-Plate 44
-
-Occurs as bristling crystals in seams and cavities in lavas; hardness,
-5.5; specific gravity, 2.2; colorless; luster vitreous; transparent on
-thin edges.
-
-Natrolite occurs as beautiful bristling tufts of needle-like crystals,
-each crystal an orthorhombic prism with a very low pyramid on the end.
-This mineral is so easily fusible that it can be melted in a candle
-flame, giving to the flame the characteristic yellow color due to
-sodium. In hydrochloric acid it dissolves to a gelatinous mass. It is
-always a secondary mineral in cavities and seams in disintegrating
-lavas, and the tuft-like manner of growth is so characteristic, that
-once seen, it will always be recognized.
-
-Natrolite is found at Weehawken and Bergen Hill, N. J., at Westfield,
-Mass., in the Lake Superior region, etc.
-
-
-Stilbite
-H₄(CaNa₂)Al₂(SiO₃)₆ + 4H₂O
-Pl. 44
-
-Usually occurs in sheaf-like bundles of fibrous crystals; hardness, 5.5;
-specific gravity 2.2; colorless to white, yellow or brown; luster
-vitreous; transparent on thin edges.
-
-Stilbite crystals are really monoclinic, but on account of almost
-universal twinning, appear as if orthorhombic. Like the two foregoing
-minerals, stilbite is found in the seams and cavities of disintegrating
-lavas. It is readily recognized by its habit of forming in sheaf-like
-bundles of fibrous crystals. It may also, but more rarely, occur in
-radiating masses. In hydrochloric acid it is completely dissolved. It is
-found in lavas, at Weehawken and Bergen Hill, N. J., in the Lake
-Superior region, etc.
-
-
-                                Calcium
-
-Calcium is one of the most abundant of metals, but never occurs as such
-in nature, nor is it used as a metal by man. In its metallic form it is
-yellowish-white, and intermediate between lead and gold in hardness.
-Exposed to air it soon tarnishes by oxidation, and in water rapidly
-decomposes the water, forming the oxide. However, it has a great
-affinity for other elements, and makes a large number of minerals, the
-most important of which are calcite, aragonite, gypsum and fluorite,
-while it is an essential component of some garnets, anorthite, epidote,
-amphibole and pyroxene. It is very widely distributed as limestone, and
-is found in solution in most all natural waters, and in the shells and
-bones of many animals and some plants.
-
-
-Calcite
-CaCO₃
-Pl. 45
-
-Occurs in well defined crystals in incrustations, and in stalactitic,
-oolitic, and granular masses; hardness, 3; specific gravity 2.7;
-colorless to white, or when impure, yellow, brown, green, red or blue;
-luster vitreous to dull; transparent on thin edges.
-
-Next to quartz, calcite is the most abundant of all minerals, and occurs
-in an almost endless variety of forms, over 300 having been described.
-It belongs to the hemihedral section of the hexagonal system, the form
-of the crystals being all sorts of variations of the rhombohedron, and
-combinations of left and right handed rhombohedrons. The cleavage is
-entirely uniform, in three directions, parallel to the faces of the
-rhombohedron, and at an angle of 74° 55′ with each other. Crystals may
-occur in the form characteristic of the cleavage, but not often. The
-commonest forms are a more or less elongated scalenohedron, made by
-combining right and left handed rhombohedrons, so that the resulting
-pyramid is six-sided, as in figure C, Plate 45. Such a scalenohedron may
-be combined with other forms in a great variety of ways. The six-sided
-prism with the ends terminated by one or more sets of rhombohedral faces
-is also fairly common. Twinning occurs occasionally.
-
-The quickest way to determine calcite is by the hardness (3), combined
-with the fact that it effervesces, when hydrochloric acid is dropped
-upon it.
-
-An interesting feature of this mineral is its marked property of
-deflecting light rays, so that a line or object placed behind a piece of
-clear calcite appears double. It was with pieces of calcite from Iceland
-that this was first seen; so that large transparent crystals of calcite
-are still called _Iceland spar_; and such calcite is used to make the
-Nichol’s prisms for microscopes, which are so useful in the study of
-minerals. This power of refracting light is present in all minerals, but
-not to such a marked degree as in calcite. The elongated scalenohedrons
-of calcite are often called “dog-toothed spar” from a fancied
-resemblance between them and the dog’s tooth.
-
-Calcite is present in solution in the water of the sea and most streams,
-from which it is withdrawn by many animals and some plants, to make
-their shells, and bones. The foraminifera, some sponges, the
-echinoderms, corals and molluscs all draw large quantities from the
-water in which they live, and build more or less permanent structures
-from it. These shells when they fall to the bottom, or after being
-broken to bits, accumulate on the bottom and make limestone, which is
-widely distributed over the country. This same limestone, when
-metamorphosed and crystalline, is marble.
-
-Calcite then is readily soluble in water, and streams flowing along
-crevices and fissures in limestone dissolve out great cavities or caves,
-like the Mammoth Cave of Kentucky. Other water, percolating through the
-limestone, comes to these cavities saturated with lime in solution and
-drips from the roofs and walls; then as part of the water evaporates, it
-deposits part of its lime in icicle-like masses, hanging from the roof.
-Such masses of non-crystalline calcite are called _stalactites_. Below
-on the floor of the cave, conical masses are built up in the same manner
-where the dripping water falls on the floor. These are _stalagmites_. In
-these limestone caves and in smaller cavities many of the most beautiful
-crystals grow. Somewhat similarly, when hot water from deep springs
-comes to the surface, it cools and can not carry as much lime, and so
-around the spring is laid down layer after layer of non-crystalline
-calcite making a mass known as _travertine_. Sometimes this is colored
-by iron or other impurities and a banded effect results. Such travertine
-as the “Suisun marble” from California, “California onyx,” “Mexican
-onyx,” and “satin spar” all belong to this class.
-
-The coral animals, especially in tropical waters precipitate an enormous
-amount of lime, until whole reefs are built of lime in this
-non-crystalline form. In places it is hundreds of feet thick and
-hundreds of miles in extent. Some of this coral has become popular for
-personal adornment. This is particularly a small, fine-grained variety,
-_Corallum rubrum_, which lives almost exclusively in the Mediterranean
-Sea. This coral is red in color, varying all the way from a deep red to
-white. It grows in small masses, three pounds being a good sized mass,
-in water 60 to 100 feet deep, requires some ten years to develop a
-full-sized mass. The making of this into beads and ornaments is an
-Italian industry. The demand is growing, while at the same time the
-supply is diminishing, and search is being widely made for more such
-coral, but up to the present time with little success. This precious
-coral is much worn as a protection against the “evil eye” and is widely
-imitated, apparently with as much protection to the wearer. When coral
-beads are offered cheap, they are probably something else, red gypsum
-being much used. This and all imitations can be readily detected by
-trying a drop of acid in the bead. Coral will effervesce, but gypsum and
-other substitutes will not.
-
-The bulk of the shells of most molluscs is made of lime, but the
-mother-of-pearl layer inside is usually aragonite. The chalk of the
-cliffs on either side of the English channel is lime, and composed of
-the shells of single celled animals. See p. 213. When lime is deposited
-in loose porous masses, as around grass, etc., and below hot springs,
-this mass is termed _calcareous tufa_.
-
-Calcite will be found almost everywhere, some of the localities for the
-finest crystals being Antwerp and Lockport, N. Y., Middletown, Conn.,
-the caves of Kentucky, Warsaw, Ill., Joplin, Mo., Hazel Green, Wis.,
-etc.
-
-
-Aragonite
-CaCO₃
-Pl. 46
-
-Occurs in crystals, in columnar or fibrous masses, or incrustations;
-hardness, 3.5; specific gravity, 2.9; colorless, white or amber; luster
-vitreous; transparent on thin edges.
-
-Aragonite has the same chemical composition as calcite, but it
-crystallizes in the orthorhombic system, either in simple forms like A
-on Plate 46, or twinned, so as to make forms which seem hexagonal. When
-in simple crystals its form easily distinguishes it from calcite and
-dolomite, but when twinned it appears much like either of these two
-minerals. From calcite it can then be distinguished by its greater
-hardness and the fact that it has cleavage in one direction only, and
-that imperfect. The cleavage is the only easy method of distinguishing
-it from dolomite. However, aragonite is most always easily distinguished
-by its habits, for it generally forms long slender crystals, which
-appear more like fibers than crystals. Neither calcite nor dolomite is
-at all fibrous.
-
-Aragonite is much less abundant than calcite, and has resulted, either
-from deposition from hot waters, or from waters having sulphates in
-solution as well as lime. Much of the travertine, and many stalagmites
-and stalactites are composed of aragonites, forming as outlined under
-calcite. The mother-of-pearl layer in the shells of bivalves is
-generally aragonite. The pearly luster of this layer is due to its being
-formed by the successive deposition of one thin layer upon another; so
-that light falling on the mother-of-pearl, penetrates, part of it to one
-layer and part to another, and is then reflected. Certain molluscs have
-this layer composed of especially thin layers, one, the _Unios_ or
-freshwater clams, the other, the “pearl oysters” or _Aviculidæ_, these
-latter, however, being only distantly related to the edible oysters. In
-the cases, where molluscs of either of these two families are of large
-size, large pieces of mother-of-pearl can be recovered, and are used for
-buttons, handles, and various ornamental objects. A further peculiarity
-of these same molluscs is the formation of pearls in the sheet of flesh,
-lining the shells. The pearls are round or rounded concretions of
-aragonite. At the center there is a grain of sand, or more often a tiny
-dead parasite. Either was an irritant to the mollusc, and to be rid of
-it, a layer of aragonite was secreted around it. Then as the mollusc
-continued to grow and secrete layers for its shell, it also added each
-time another layer around the sand-grain or parasite, until in time a
-pearl of noticeable, and then of considerable size resulted. These have
-all the pearly luster of the mother-of-pearl in a sphere which tends to
-make the luster even more marked.
-
-Pearls were in use as ornaments in China some twenty-three centuries
-before Christ, and in India over 500 B.C. They were very highly prized
-by the Romans and since their times the rulers of India have shown a
-remarkable fondness for them. Today the finest come from the Gulf of
-Persia and the Red Sea, while still others are found about Australia and
-in the Caribbean Sea. In the United States not a few are collected every
-year from the fresh water clams, some of them beautifully tinted with
-pink or yellow.
-
-Aragonite is found widely, as at Haddam, Conn., Edenville, N. Y.,
-Hoboken, N. J., New Garden, Penn., Warsaw, Ill., etc.
-
-
-Anhydrite
-CaSO₄
-Pl. 46
-
-Occurs in cleavable or granular masses, rarely in crystals; hardness,
-3-3.5; specific gravity, 2.9; color white, gray, bluish or reddish;
-luster pearly on cleavage faces; transparent on thin edges.
-
-When anhydrite occurs in crystals, they are orthorhombic, like the
-diagram on Plate 46. Usually, however, it is found in beds or layers,
-which were deposited by the evaporation of sea water, and so it is
-associated with salt. Anhydrite has three cleavage planes which are at
-right angles to one another, which produce rectangular or cube-like
-forms. Mostly anhydrite is associated with gypsum, from which it differs
-by its greater hardness, pseudo-cubic cleavage, and the fact that
-anhydrite is not readily soluble in acid, while gypsum is. Chemically it
-differs from gypsum in not having water of crystallization, which gypsum
-does have. The anhydrite is likely to occur as veins and irregular
-masses in beds of gypsum. Calcium sulphate is precipitated from sea
-water when 37% of the water has been evaporated, and it may be deposited
-either as anhydrite or as gypsum, the factors, which decide as to which
-of these two minerals it will be, being as yet unknown. After
-deposition, if exposed to moisture, the anhydrite may change to gypsum,
-irregular masses often remaining unchanged.
-
-It is found in salt mines in Elsworth Co., Kan., in limestone cavities
-at Lockport, N. Y., in veins in Shasta Co., Calif., etc.
-
-
-Gypsum
-CaSO₄ + 2H₂O
-Pl. 47
-
-Occurs in crystals, in cleavable masses, or in fibrous masses; hardness,
-2; specific gravity, 2.3; colorless, white, amber, gray, or pink; luster
-vitreous, silky or pearly; transparent on thin edges.
-
-Gypsum crystals are monoclinic as seen on Plate 47, the perfect ones
-usually occurring in clay, as at Oxford, O., or in cavities; while
-crystals of less perfect outline, but with fine cleavages, are found in
-Utah, Kansas, and Colorado. The cleavage is very perfect in one
-direction, making it possible to strip off thin sheets almost like mica,
-and less perfect in two other directions, which appear on the smooth
-surface of the first cleavage as lines intersecting at 66° 14′. Twinning
-is also common in such a way, that the two united crystals make forms
-similar to arrowheads. These cleavages and the twinning show nicely in
-the photograph of gypsum on Plate 47.
-
-Gypsum is distinguished from anhydrite by its lesser hardness, its
-cleavage and by being soluble in acids.
-
-Most gypsum occurs in beds or granular masses which were deposited from
-evaporating sea-water, coming down when 37% of the water was lost. Such
-beds are often very extensive and are quarried as a source of gypsum to
-make plaster of Paris, stucco, neat plaster, Keene’s cement, plaster and
-wall board, partition tiles, etc. The use of the gypsum for plaster of
-Paris and all these other uses is based on its affinity for water of
-crystallization. The gypsum is first heated to about 400° C., which
-drives off the water of crystallization, and causes it to crumble to a
-powder, which is the plaster of Paris. When water is added, it is taken
-up and the powder “sets,” or recrystallizes back to gypsum. This simple
-reaction has made it very useful, for making moulds, casts, hard finish
-on walls, as stucco, etc.
-
-When the granular type of gypsum is fine grained, it is known as
-_alabaster_, which is used for carving vases, statuettes, ornaments,
-etc. The fibrous variety is called _satin spar_, and is sometimes used
-for cheap jewelry and ornaments, but it is very soft and quickly wears
-out. At Niagara Falls there is a considerable trade in objects carved
-from this satin spar, tourists buying them on the assumption that the
-mineral is native and comes from under the falls. Most of it, however,
-comes from Wales, the small amount of gypsum of that region being mostly
-granular.
-
-Gypsum is found all across the United States, as in New York, Michigan,
-Virginia, Ohio, Alabama, South Dakota, Wyoming, Colorado, Utah,
-California, etc.
-
-
-                          The Strontium Group
-
-Strontium is a pale-yellow metal, ductile and malleable, but oxidizing
-quickly when exposed to the air. It does not occur in its native state
-in Nature, but always as some compound, usually either the carbonate or
-sulphate. It resembles barium, but differs in giving to the flame a
-brilliant red color, on which account the compounds of strontium are
-used mostly in making red fire in fireworks.
-
-
-Strontianite
-SrCO₃
-
-Occurs in needle-like crystals, or in columnar or fibrous masses;
-hardness, 3.5-4; specific gravity, 3.6; color white, pale-green or pale
-shades of yellow; luster vitreous; transparent on thin edges.
-
-Strontianite is orthorhombic, but appears as if hexagonal, since its
-general habit is to have three twin crystals grow together in such a way
-as to make a six-sided double pyramid. In this it is very like
-witherite, both these minerals appearing externally much alike. They can
-be readily distinguished, however, by holding a piece in the flame. If
-it gives a red color to the flame it is strontianite, if green, it is
-witherite. It effervesces readily in hydrochloric acid.
-
-Strontianite is found in veins and cavities in limestone, where it has
-been deposited after being leached from the limestone by percolating
-waters. Though known at several localities it is not now being mined in
-this country, what we use being imported mostly from Germany.
-
-It is found at Schoharie, Chaumont Bay and Theresa, N. Y., in Mifflin
-Co., Penn., etc.
-
-
-Celestite
-SrSO₄
-
-Occurs in crystals, cleavable masses and fibrous; hardness, 3; specific
-gravity, 3.9; colorless, white, pale-blue, or reddish; luster vitreous;
-transparent on thin edges.
-
-Celestite, the sulphate of strontium, is very like barite in external
-appearance and habit. It is orthorhombic and occurs in tabular crystals.
-Its cleavage is perfect on the basal plane, and imperfect in one other
-direction. The ready way of distinguishing celestite from barite is to
-hold a piece in the flame. If it is celestite it will color the flame
-red, if barite, green.
-
-Celestite is mostly found in veins or cavities in limestone, where it
-has been deposited by percolating waters, after having been leached from
-the limestone. Some years ago an important deposit of celestite was
-found on Strontian Island in Lake Erie, but that was soon worked out and
-now no veins are being worked in this country. It is also found at
-Chaumont Bay, Schoharie and Lockport, N. Y., in Kansas, Texas, West
-Virginia, Tennessee, etc.
-
-
-                            The Barium Group
-
-Barium is another metal which does not occur in its native state in
-Nature. It has only been isolated as a yellow powder, which, exposed to
-air or water, soon changes to one of the oxides. Both barium and its
-compounds are peculiar in causing a green color, whenever exposed to the
-flame. Two of its compounds are fairly abundant, the sulphate, barite,
-and the carbonate, witherite. The former is the more abundant and has
-come to be fairly widely used, something over 100,000 tons being
-annually consumed in the United States, to make the body in flat finish
-paints for interior work and light colors, for a filler in rubber goods,
-linoleum, oil cloth, glazed paper, and for a wide range of chemical
-compounds.
-
-
-Barite
-BaSO₄
-Pl. 48
-_heavy spar_
-
-Occurs in crystals or in lamellar, nodular or granular masses; hardness
-3; specific gravity, 4.5; colorless, white or almost any color; luster
-vitreous; transparent on thin edges.
-
-Barite occurs in orthorhombic crystals, which are tabular in form, and
-usually have the edges beveled, as in figure A, Plate 48. There is
-cleavage in three directions, a rather perfect basal cleavage, and two
-less perfect cleavages, which are at right angles to the basal cleavage
-plane, and intersect each other at 78°.
-
-The tabular form, the cleavage, the heavy weight, and the fact that a
-piece of barite put into the flame colors it green, all serve to
-distinguish this mineral.
-
-Barite is a secondary mineral of aqueous origin, which has been
-deposited in veins and cavities in igneous, metamorphic, or sometimes
-sedimentary rocks. It is most likely to occur in veins in igneous or
-metamorphic rocks, the barium having been dissolved from certain
-feldspars and micas by percolating water, and then redeposited in the
-fissures, as the water came into them. If in sedimentary rocks, the
-barite veins are usually in limestones. Barite is quite likely to be a
-gangue mineral for the ores of lead.
-
-It is found at Hatfield and Leverett, Mass., Cheshire, Conn., Pillar
-Point, N. Y., Cartersville, Ga., in Virginia, North Carolina, South
-Carolina, Missouri, Kentucky, Tennessee, Alabama, Illinois, Wisconsin,
-Nevada, California, Alaska, etc.
-
-
-Witherite
-BaCO₃
-Pl. 48
-
-Occurs in crystals, or in granular or columnar masses; hardness, 3.5;
-specific gravity, 4.3; color white to gray; luster vitreous; translucent
-on thin edges.
-
-Witherite is not an abundant mineral. Its crystals are really
-orthorhombic, but they are usually twinned, three crystals growing
-through each other in such a manner that the resulting crystal appears
-like a six-sided double pyramid, similar to the one figured on Plate 48.
-The commonest mode of occurrence is in compact masses. Witherite
-effervesces when cold acid is dropped upon it, which, with its heavy
-weight, and the green color it gives to the flame, serves to distinguish
-the mineral. It is used for medicines, in chemical industries, and a
-considerable amount is made into rat poisons. The chief locality for
-witherite is in northern England, but in this country it is found along
-with barite, especially at Lexington, Ky., and in Michigan.
-
-
-                                 Carbon
-
-Carbon is an element widely distributed in nature, occasionally
-appearing in its elementary form, as graphite or the diamond, but much
-more important in its compounds. Small quantities are present in the air
-as carbon dioxide, CO₂, immense quantities occurring in the carbonate
-minerals, which have been considered under their respective metallic
-salts, as calcite, malachite, siderite, cerrusite, smithsonite,
-witherite, etc., and still other large quantities being represented in
-organic compounds, which occur as rocks under the heads of petroleum,
-coal, etc. The occurrence of limestones, graphite, coal or petroleum is
-always indicative of the activity of living organisms, and in some cases
-is the only indication of life in the earlier rocks.
-
-
-Graphite
-C
-_Plumbago_
-
-Occurs in hexagonal scales or flakes, in layered masses, or earthy
-lumps; hardness, 1; specific gravity, 2.1; color black or steel-gray;
-streak gray; luster metallic; opaque on thin edges.
-
-Like the diamond graphite is pure carbon, but in this case it is in
-non-crystalline form. It occurs in both igneous and metamorphic rocks.
-In the former case it is either in flakes in the rock, or in veins, and
-has been derived directly from the molten magmas, having either
-precipitated in the hardening granite or lava, or having been carried
-into the fissures and there precipitated to make the veins of graphite.
-In either case the graphite probably represents organic deposits which
-have been melted into the igneous magma at the time of its formation.
-Graphite may also occur in metamorphic rocks, beds of coal or other
-organic deposits being altered by the heat. Such beds are often of
-considerable extent and economic importance.
-
-The extreme softness, greasy feel, and the dark-gray streak readily
-distinguish graphite.
-
-It is widely used in making crucibles and furnace linings for foundries,
-lead pencils, paint, lubricating powders, etc.
-
-Graphite is found at Brandon, Vt., Sturbridge, Mass., Ashford, Conn., in
-Essex, Warren and Washington Cos., N. Y., Clay, Chilton and Coosa Cos.,
-Ala., Raton, N. M., Dillon, Mont., etc.
-
-
-Diamond
-C
-
-Occurs in octahedral crystals; hardness, 10; specific gravity, 3.5;
-colorless to yellow, brown, blue, etc., luster adamantine; transparent
-on thin edges.
-
-Like graphite the diamond is pure carbon, but in this case in crystal
-form. It is the hardest of all minerals, and as brilliant as any; so
-that in spite of being by no means the rarest, it may easily be
-considered the most popular of all gems. Tiny diamonds have been made
-artificially under great heat and pressure; so that this mineral is
-thought of as forming in Nature in dark igneous lavas at great depths.
-The diamond has good cleavage parallel to the octahedron faces, and, in
-spite of some traditions to the contrary, is brittle.
-
-There are not many diamond localities, the most famous being the
-Kimberley district of South Africa, which produces many times as many
-diamonds as all the others put together, though all the time some are
-being found in Borneo and Brazil. A very few have been found in the
-United States, only one locality however yielding them in the original
-matrix. That is at Murfreesboro, Ark., where they are mined in a
-disintegrating peridotite (a dark lava, mostly peridot), which has been
-extruded through the sedimentary rocks of that region. This matrix is
-similar to the “blue earth,” the matrix of the diamonds of South Africa,
-which occurs in “pipes,” representing the necks of ancient volcanoes.
-The American diamonds are of small size, averaging considerably less
-than a third of a carat in weight, which does not allow great value to
-the individual diamonds.
-
-From time to time, especially large diamonds have been found in
-different parts of the world, the largest being the Cullinan diamond,
-found at the Premier Diamond Mine of South Africa. It weighed 3025
-carats or about a pound and a quarter, and was valued at over
-$3,000,000. It was presented to King Edward VII, who had it cut into 11
-brilliants, four of which are larger than any other diamond yet found.
-Other famous diamonds, like the Kohinoor, 106 carats, found in India in
-1304; the Regent, 136 carats, also found in India; the Orloff, 193
-carats, set in the eye of an Indian idol; the South Star, 125 carats,
-the largest ever found in Brazil; the blue Hope, etc., have in many
-cases romantic and interesting stories woven about them.
-
-Though for ages diamonds have been highly prized gems, it is only in
-comparatively recent times that cutting and polishing have been resorted
-to, for the purpose of enhancing their brilliancy. This is done by
-grinding reflecting faces on the original stone, by the aid of discs of
-iron or tin in which diamond dust has been embedded. Diamond chips and
-cloudy or imperfect diamonds are used for making tools for cutting
-glass, rock drills, etc.
-
-
-                               Phosphorus
-
-The element phosphorus at ordinary temperatures is an almost colorless,
-faintly yellow, solid substance of glistening appearance and waxy
-consistency. In Nature it does not occur pure, but always as one of its
-compounds. It is of great importance to man for it is one of the
-essentials for plant growth and also for the higher animals, being
-required for the bones and to some extent for nervous tissue. Originally
-it is found in all the igneous rocks. Some of the phosphorus is removed
-by solution and carried to other regions and to the sea. From this
-distribution it comes into the sedimentary rocks, and, when they are
-altered by heat, into the metamorphic rocks. Thus it has a wide, though
-by no means even, distribution. The soils formed by disintegration of
-these rocks probably all have some phosphorus in them; but where there
-is vigorous plant growth, it soon tends to become exhausted, and must be
-renewed. For this reason the use of phosphates has become of prime
-importance in Agriculture. The possession of beds of rock carrying
-phosphorus has come to be of international importance. The United States
-is particularly fortunate in this respect, and produces over 25% of the
-world’s supply of phosphates. Most all the phosphorus is recovered
-either from phosphate minerals, the most important of which is apatite,
-or from the non-crystalline and impure mixtures of phosphate minerals
-and other substances, discussed under phosphate rock.
-
-
-Apatite
-Ca₅F(PO₄)₃
-Pl. 49
-
-Occurs in crystals, concretionary nodules, or in bedded masses;
-hardness, 5; specific gravity, 3.2; color reddish-brown or green, rarely
-white or colorless; luster vitreous; translucent on thin edges.
-
-Apatite occurs in hexagonal prisms, usually with the ends truncated by a
-basal plane, and with one or more sets of pyramidal faces between the
-prism and the basal plane. Crystals range in size from tiny to over a
-foot in diameter. There is but one cleavage and that is basal. The
-crystal form, cleavage, and hardness will easily determine this mineral.
-Apatite is usually associated with igneous or highly metamorphic rocks,
-such as granites, gneisses, and crystalline limestones. While the
-phosphoric acid of apatite is highly desirable for use in fertilizers,
-the crystals do not occur in sufficient abundance to make them
-commercially available, and non-crystalline phosphate rocks are resorted
-to for this purpose.
-
-Crystals of apatite are found at Norwich and Bolton, Mass., Rossie and
-Edenville, N. Y., Suckasunny and Hurdstown, N. J., Leiperville, Penn.,
-Wilmington, Del., etc. Templeton, Canada, is perhaps the best known
-locality for fine apatite.
-
-
-Turquois
-H₅[Al(OH)₂]Cu(OH)(PO₄)₄
-
-Occurs in seams and incrustations; hardness, 6; specific gravity, 2.7;
-color bluish-green; streak blue; luster waxy; translucent to opaque on
-thin edges.
-
-In this country this complex phosphate of aluminum and copper is found
-in streaks and patches in volcanic rocks, but in Persia comes from
-metamorphic rocks. To the Persians it was a magical stone, protecting
-the wearer from injuries, and among the Pueblo Indians it was regarded
-as of religious value in warding off evil. The best turquois comes from
-Persia, but it has been found at several points in the United States, as
-in Los Cerrillos and Burro Mts., N. M., in Mohave Co., Ariz., San
-Bernardino Co., Cal., in Nevada and Colorado.
-
-
-                                Fluorine
-
-At ordinary temperatures the element fluorine is a colorless gas, which
-was not obtained pure until 1888, because it could not be contained in
-vessels of glass, gold, platinum, etc. At that time it was made and kept
-in a vessel composed of an alloy of platinum and iridium. Its most
-important compound is hydrofluoric acid, a fuming liquid, which is
-mostly used to etch or dissolve glass. It occurs in several minerals,
-like tourmaline, turquois, etc., but the only one used to obtain the
-hydrofluoric acid is fluorite.
-
-
-Fluorite
-CaF₂
-Pl. 50
-_Fluor spar_
-
-Occurs in crystals and cleavable masses; hardness, 4; specific gravity,
-3.2; colorless or some shade of violet, green, yellow, or rose; luster
-vitreous; transparent on thin edges.
-
-Fluorite usually occurs in beautiful cubic crystals, often with the
-edges and corners beveled by smaller faces, and occasionally in twins,
-which seem to have grown through each other. There is perfect cleavage
-parallel to each of the octahedral faces, which often, as in the
-illustration on Plate 50, show as cracks cutting off the corners.
-
-Since fluorite loses weight and color on heating, it is concluded that
-the colors are due to the presence of hydrocarbon compounds. The red and
-the green fluorite when heated to above 212° F. become phosphorescent,
-as may be seen if they are thus heated and exposed to the light, then
-taken into the dark.
-
-Fluorite is quite commonly the gangue mineral associated with metallic
-ores, and is also likely to occur with topaz, apatite, etc. It is
-generally in such places that it seems to have been deposited from hot
-vapors, rising from igneous magmas.
-
-It is the only mineral at all common from which fluorine can be
-obtained, and is used for making hydrofluoric acid, and other chemical
-compounds of this element. It is, however, of much greater importance as
-a flux in reducing iron, silver, lead and copper ores. In the industries
-it finds a place, being used to make apochromatic lenses, cheap jewelry,
-and for the electrodes in flaming arc lamps.
-
-Fluorite is widely distributed, some of the better known localities
-being Trumbull and Plymouth, Conn., Rossie and Muscalonge Lake, N. Y.,
-Gallatin Co., Ill., Thunder Bay, Lake Superior, Missouri, etc.
-
-
-Halite
-NaCl
-Pl. 50
-_Salt_
-
-Occurs in crystals, and in cleavable and granular masses; hardness, 2.5;
-specific gravity, 2.1; colorless to white; luster vitreous; transparent
-on thin edges.
-
-Halite is common salt, occurring in cubic crystals, with perfect cubic
-cleavage. Its form, hardness, taste, and solubility in water make it
-easy to determine.
-
-Halite is the most abundant salt in sea water, making about 2.5% out of
-the total of 3.5% of solids in solution. It is also a prominent, when
-not the leading, salt in solution in the waters of inland lakes, like
-Great Salt Lake, or the Dead Sea, there being 20% of halite in the
-former and 8% in the latter, though the total of solid in solution in
-the water of the Dead Sea is greater than that in Great Salt Lake.
-
-The great salt deposits are mostly the result of the evaporation of the
-water of arms or isolated portions of former oceans; the salt, gypsum,
-etc., left by the drying sea, having been buried beneath later
-sediments. Other bodies of salt represent the disappearance of ancient
-lakes. There are also the curious “salt domes” of Louisiana and Texas,
-which are immense, roughly circular, subterranean masses of salt
-extending to as yet unknown depths which are thought to have been formed
-by masses of salt from some deep source bed pushing their way upward
-through the overlying formations by plastic flowage. As the upthrust
-took place the sediments were arched into domes. Some of these domes are
-today important sources of rock salt.
-
-There are extensive beds of salt under parts of New York, Michigan,
-Ohio, Oklahoma, Kansas, etc., which are mostly worked by drilling wells
-into the salt layer, then introducing hot water to dissolve the salt.
-The brine thus formed is pumped to the surface, and the salt recovered
-by evaporation in pans. During the process, skeleton crystals of salt
-with concave faces may form, but in Nature the crystals are uniformly
-solid cubes.
-
-
-Boracite
-Mg₇Cl₂B₁₆O₃₀
-
-Occurs in small crystals or granular masses; hardness of crystals, 7; of
-the masses, 4.5; specific gravity 3; colorless to white; luster
-vitreous; transparent to translucent on thin edges.
-
-Small crystals, associated with salt and gypsum, occur in the beds and
-incrustations, which result from the drying up of alkaline lakes,
-especially in Nevada and southern California. The crystals are
-orthorhombic, but appear like perfect cubes, with the edges beveled and
-part of the corners cut. They are not easily dissolved in water, but
-quickly go into solution in hydrochloric acid.
-
-
-Colemanite
-Ca₂B₆O₁₁ + 5H₂O
-
-Occurs in crystals or compact masses; hardness, 4.5; specific gravity,
-2.4; colorless to white; luster vitreous; translucent on thin edges.
-
-The crystals when they occur, are monoclinic; but usually colemanite is
-a bedded deposit, which has resulted from the drying up of a saline
-lake. It was first found in Death Valley, Cal., in 1882, then near
-Daggett, Cal., and since then in several similar locations in Nevada and
-Oregon. The deposits are of all grades of purity, the colemanite being
-mixed with varying quantities of mud. Today this mineral is the chief
-source of borax, which is used in medicines, cosmetics, colored glazes,
-enamel, and as a preservative.
-
-
-Borax
-NaB₄O₇ + 10H₂O
-
-Occurs in crystals or in powdery incrustations; hardness, 2; specific
-gravity, 1.7; colorless to white; luster vitreous; translucent on thin
-edges.
-
-The crystals are tiny and monoclinic, this mineral being usually
-obtained by the evaporation of the saline waters of such lakes as Clear
-and Borax Lakes in southern California, or from the muds of salt
-marshes, like Searles Borax Marsh in California. Originally most of our
-borax came from a large saline lake in Tibet, but now most of it is
-obtained from colemanite. Borax is soluble in water, giving it a
-sweetish taste.
-
-
-Sulphur
-S
-Pl. 51
-
-Occurs in crystals, incrustations or compact masses; hardness, 2;
-specific gravity, 2; color yellow; streak yellow; luster resinous;
-translucent on thin edges.
-
-Aside from the numerous compounds, such as the sulphides of the metals
-like pyrite, galena, sphalerite, etc., and the sulphates, like gypsum,
-barite, anglesite, etc., sulphur occurs in its elemental form in Nature.
-In this case it may be in crystals, which are orthorhombic and usually
-occur as octahedrons, with the upper and lower ends truncated, either by
-a basal plane, or by a lower octahedron, or by both. Incrustations and
-compact masses are, however, much the commoner mode of occurrence. The
-incrustations are found mostly about volcanic regions, where the sulphur
-has risen from the molten lavas as a sublimate, and on cooling has been
-deposited in crevices or on the adjacent surfaces. Irregular masses of
-sulphur are often found where sulphide minerals, like pyrite or galena
-have been decomposed in such a way as to leave the sulphur behind. The
-extensive beds of sulphur are usually associated with gypsum, and are
-thought to be the result of water, containing bituminous matter, so
-acting on gypsum as to remove the calcium and oxygen as lime, and leave
-the sulphur. Finally many waters carry sulphates in solution, from which
-the sulphur may be precipitated by certain sulphur bacteria, making thus
-incrustations on the bottom of ponds or lakes.
-
-Sulphur is used for making matches, gunpowder, fireworks, insecticides,
-in medicine, vulcanizing rubber, etc. It is widely distributed, however,
-most of the present world’s production is from deposits associated with
-the “salt domes” of Texas and Louisiana. A “caprock” of gypsum and
-anhydrite overlies many of these which often contains elemental sulphur.
-Wells are drilled into this, and the sulphur is melted by the
-introduction of hot steam. This melted sulphur is then pumped to the
-surface and run into molds.
-
-Some of the best known localities are Sulphurdale, Utah, Cody and
-Thermopolis, Wyo., Santa Barbara Co., Cal., Humboldt Co., Nev., and
-about the hot springs of the Yellowstone Park.
-
-
-Ice
-H₂O
-Pl. 51
-_water_
-
-Occurs solid as ice, snow and frost, or liquid as water; hardness, 2;
-specific gravity, .92; colorless to white; luster adamantine;
-transparent on thin edges.
-
-Though we seldom think of ice, and its liquid form, water, as a mineral,
-still it is one, and perhaps the most important of all minerals, as well
-as the most common. Ice melts at 32° F. and vaporizes at 212° F., being
-then termed steam. Because it is so common and liquid at ordinary
-temperatures it acts as a solvent for a host of other minerals, and is
-therefore the agent by which they are transported from place to place
-and redeposited in veins and beds.
-
-Not only does water act as a transportation agent for minerals in
-solution, but is also the agent of erosion and weathering. Water
-vaporizes slowly when exposed to the air at all temperatures above
-freezing, and so it is slowly rising from the surface of the sea or
-lakes or moist ground into the air, where it would accumulate until the
-air was saturated, if the air would only keep still and at a uniform
-temperature. The air will hold a given amount of water vapor, which is,
-for example, 17 grams per cubic meter when the temperature is 68° F.,
-but at 59° F. it will hold only 12½ grams, or at 50° F. only 9 grams.
-Thus the air is more or less completely saturated at higher
-temperatures, and when the temperature is lowered the air can not hold
-all it has taken up, and it is precipitated in dew, rain or snow, most
-often as rain. When the rain falls it mechanically carries away, and
-more or less slowly transports to other places particles of rock, being
-thus the agent of erosion; and when it is slowed down, as on entering
-the quiet water of a lake or the sea, it drops the mechanically carried
-sediment and makes sedimentary deposits.
-
-Another very important and unique feature of water is that on freezing
-it expands about ¹/₁₁th of its former bulk, so that, as a result, ice
-floats, and also wherever water in crevices is frozen, the crevices are
-enlarged. In locations where this freezing and melting take place
-repeatedly throughout a year, there the breaking up of rocks is rapid.
-
-This is hardly the place to take up a complete discussion of water, but
-its action as a solvent, mechanically, and in freezing, melting, and
-vaporizing is the basis of a large part of the study of geology.
-
-When water crystallizes, as in forming ice, it is in the hexagonal
-system. It tends to twinning and a snow-flake is made up of a large
-number of twinned crystals, each diverging from the other at 60°. When
-ice is formed in the air or on the surface of water it forms these
-complex and beautiful multiple twins, of which but a couple are
-suggested here. Beneath the surface the hexagonal crystals grow downward
-into the water, parallel to each other, making a fibrous structure,
-which is very apparent when ice is “rotten,” which is the time at which
-the surfaces of the prisms are separating, because the molecules leave
-the crystal in the reverse order to which they united with it. Frost in
-marshy or spongy ground will often show this fibrous growth beautifully.
-
-
-
-
-                               CHAPTER IV
-                               THE ROCKS
-
-
-Broadly speaking a rock is an essential part of the crust of the earth,
-and includes loose material, like sand, mud, or volcanic ashes, as well
-as compact and solid masses, like sandstone and granite. Rocks are
-aggregates of minerals, either several minerals grouped together, as are
-mica, quartz and feldspar to make granite, or large quantities of a
-single mineral, like quartz grains to make sandstone.
-
-The rocks are most conveniently classified according to their mode of
-origin, into three main groups, igneous, sedimentary, and metamorphic.
-The igneous rocks are those which have solidified from a molten magma,
-like lavas, granites, etc. The sedimentary rocks are those which
-represent accumulations of fragments or grains, derived from various
-sources, usually the weathering of other rocks, and deposited by such
-agents as water, wind and organisms. Metamorphic rocks are those which
-were originally either igneous or sedimentary, but have been altered by
-the actions of heat, pressure and water, so that the primary character
-has been changed, often to such an extent as to be obscured.
-
-Rocks once formed in any of the above ways are being constantly altered
-in character by the various processes of nature. Those exposed on the
-surface are weathered to pieces, and the fragments are transported by
-wind or water to accumulate elsewhere as sedimentary rocks. Those buried
-deep beneath the surface are affected by the high temperature and
-pressure of the depths of the earth and thus metamorphosed. For instance
-a granite exposed on the surface is slowly weathered, some parts being
-carried away in solution by the rain water, others less soluble
-remaining as grains of quartz, mica or kaolin. These are transported by
-water and sorted, the finer kaolin being carried to still and deep
-water, the quartz and mica accumulating in some lowland as sand. This
-sand will in time be cemented to a sandstone, later slowly buried
-beneath the surface. If buried deep it will feel the effect of the
-interior temperature, which increases as one goes down at the rate of
-one degree F. for every 50 feet. If this should be in a region where
-folding and mountain-making takes place, the material under the folds
-would be melted (because of the relief from pressure which would permit
-the high temperature to act freely) and become igneous rock, either
-coming to the surface as lava, or remaining below the surface and making
-a granite or similar rock; while the sedimentary material not melted but
-near enough to the molten material to be affected, would be
-metamorphosed, in this case to a quartzite. Much of the interest and
-profit in studying rocks, will come from the understanding which they
-will give as to the history of that particular part of the earth’s crust
-where they are found.
-
-
-                             Igneous Rocks
-
-Igneous rocks are those which have formed from material that has been
-melted, which involves temperatures around 1300° C.; or, if there is
-water in the original material, temperatures as low as 800° C. will
-suffice. Considering the increase of temperature to be a degree for
-every 50 feet downward, this involves the rocks having been at depths of
-5 to 10 miles below the surface. While at such depths the temperature
-must be high enough to melt rocks, the great pressure of the overlying
-rocks seems to keep them solid; for we know that the center of the earth
-is solid, as is shown by a variety of observations, such as the rate at
-which earthquake waves are transmitted through the earth, the lack of
-tidal effects, etc. However, there is every reason to believe that if
-the pressure is removed from the rocks which are five to ten miles below
-the surface, there is heat enough at those depths to melt them. When the
-crust of the earth is folded, as when mountain ranges are formed, the
-areas under the arches or upward folds are relieved of pressure. Then
-those rocks, which are under the arches and are relieved, become molten.
-The molten magma may well up and fill the space beneath the arch where
-it would cool again very slowly; or, if there is fissuring during the
-folding, some of the molten material may be forced out through the
-fissures and pour out over the surface as lava. Another area in which
-pressures may be locally relieved is in the region of faulting, where
-the crust of the earth is broken into blocks, between which there are
-readjustments, some being tipped one way, some another, some uplifted.
-Here again there would be areas of relieved pressure and molten magmas
-would form, some of them solidifying in place, others rising to the
-surface.
-
-The molten material is termed the magma, and when it reaches the
-surface, great quantities of water vapor and other gases escape: or
-these gases may even escape from magmas which do not reach the surface,
-rising through fissures. As these hot vapors pass through the fissures,
-they are cooled, and may deposit part or all of their dissolved
-compounds in the fissure, making veins. Lava is the magma minus the
-vapors. Magmas vary greatly from place to place, indicating that they
-are formed locally and do not come from any general interior reservoir,
-as has sometimes been suggested.
-
-When the molten magmas escape to the surface, they are termed extrusive,
-and as they spread out in a layer this is termed a sheet. This rise and
-overflow may be quiet, and from time to time one outpouring may follow
-another making sheet after sheet. Or after one outpouring, the pressure
-below may cease for a time and allow the lava to solidify and make a cap
-or cover over the opening. Before more lava can rise, this cover must be
-removed. This usually happens in an explosive manner, the lava below,
-with the increasing pressure exerted by its expanding gases, finally
-exerting enough pressure, so that the cover is broken, or shattered and
-thrown in thousands of fragments into the air, as happened at Mt. Pelée
-on the Island of Martinique in 1902. The fragments thrown into the air
-are often termed volcanic ashes, though this is not a good word for
-them, for they have not been burned.
-
-In case the molten magmas under the relieved areas do not reach the
-surface they are termed intrusive. Such magmas may remain in the space
-under a mountain fold, or be forced in fissures part way to the surface.
-When the magma is forced into more or less vertical cracks and there
-solidifies, and these are exposed by erosion, they are termed dikes.
-Sometimes the magmas have risen part way to the surface and then pushed
-their way between two horizontal layers of rock and there hardened, in
-which case they are termed sills, when uncovered. The Palisades along
-the Hudson River are the exposed edge of a sill. Again the molten magmas
-may well up and spread between two horizontal layers, but come faster
-than they can spread horizontally, and then the magma takes the form of
-a half sphere, and the overlying layers of rock are domed up over it.
-Such a mass is termed a laccolith. In all these cases the mass of
-igneous rock is only discovered when the overlying rocks have been
-eroded off. The great mass of molten magma under the arches of mountain
-ranges simply cools slowly into a granitic type of rock. These masses
-are exposed when the thousands of feet of overlying rock are eroded off.
-When these masses are exposed, if of but a few miles in extent, they are
-called stocks, but, if of many miles in length and breadth, they are
-batholiths, and are very characteristic of the heart of mountain ranges.
-
-In all the above cases the exterior of the molten mass cools first, and
-forms a shell around the rest. The shell determines the size of the
-mass. As the cooling continues into the interior, it also solidifies,
-and as all rocks shrink on cooling, cracks develop, separating the mass
-into smaller pieces. There is usually no regularity about these cracks
-and the mass is divided into blocks from six inches to three feet in
-diameter. However, in some cases, especially in sills and laccoliths
-where the cooling is slower, the shrinkage may be marked by a regular
-system of cracks which bound the rock into more or less regular
-hexagonal columns. The Palisades and the Devil’s Tower in Wyoming (See
-Plate 52) show this structure. The Devil’s Tower is the remnant of a
-laccolith, all except the central core of which has been eroded away.
-All of the above terms have nothing to do with composition, but refer
-entirely to the manner of occurrence.
-
-While the igneous rocks are classified according to their composition,
-the rate at which they cooled has much to do with their texture, and
-certain names apply to the texture. For instance when the molten lava
-cools very rapidly, there is no time for the formation of crystals, and
-the resulting rock is glassy or non-crystalline. If the cooling is slow
-as in large bodies, crystals have time to form and grow to considerable
-size as in granites. Between these all grades may occur; and one
-classification of igneous rocks expresses their rate of cooling, in such
-terms as the following.
-
-Glassy—lavas which have cooled so quickly that they are without distinct
-crystallization, such as obsidian, pitchstone, etc.
-
-Dense or felsitic—lavas which have cooled less rapidly, so that crystals
-have formed, but in which the crystals are too small to be identified by
-the unaided eye, such as felsite or basalt.
-
-Porphyritic—magmas from which, in solidifying, one mineral has
-crystallized out first and the crystals have grown to considerable size,
-while the rest have remained small.
-
-Granitoid—magmas which have solidified slowly, so that all the minerals
-have crystallized completely, and the component crystals are large
-enough to be recognized readily, as in granite.
-
-Fragmental—a term applied to the fragments which have resulted from
-explosive eruptions of igneous rocks. These fragments may be loose or
-consolidated. Volcanic ashes are typical.
-
-Porous—a term applied to the lava near the upper surface, which is
-filled with gas cavities, such as pumice.
-
-Amygdoloidal—is the term applied to porous lavas, when the cavities have
-been filled by other minerals, such as calcite or some of the zeolites.
-
-
-In determining a rock, first decide whether it is igneous, sedimentary
-or metamorphic. The igneous character is recognized by its being either
-glassy, or composed of masses of crystals irregularly arranged, there
-being neither layering nor bedding.
-
-
-                    CLASSIFICATION OF IGNEOUS ROCKS
-
-   Texture                         Excess of light colored minerals                                   Excess of dark colored minerals
-
- Glassy       obsidian, perlite, pumice, pitchstone                                       scorias, trachylyte, basalt-obsidian
-
-                      Feldspar orthoclase                                Feldspar Plagioclase                                 No feldspar
-              Mica and/or hornblende and/or augite         Mica and/or hornblende               with pyroxene          augite and/or hornblende
-                                                                                                                              and/or mica
-                   +quartz            -quartz           +quartz            -quartz           +olivine      -olivine   +olivine       -olivine
-
- Dense        rhyolite           trachite           dacite (felsite)  andesite (felsite)  basalt                                 augitite or
-                                                                                                                                 hornblendite
- Porphyritic  rhyolite-porphyry  trachite-porphyry  dacite-porphyry   andesite-porphyry   basalt-porphyry                        augitite-porphyry
- Granitoid    granite            syenite            quartz-diorite    diorite             olivine-gabbro   gabbro    peridotite  pyroxenite
- Fragmental   rhyolite, tuff     trachite, tuff     Dacite, tuff or   andesite tuff or    Basalt tuffs and breccias
-              or breccia         or breccia         breccia           breccia
-
-When it is located as igneous, turn to the key on page 177 and decide as
-to which type of texture is present. If glassy, the color, luster and
-type of construction will place it. If the rock is crystalline, first
-decide whether feldspar is present, and if present, what type: then
-determine the dark mineral, and lastly whether quartz or olivine is
-present. In dense rocks the presence of quartz may be determined by
-trying the hardness, for none of the other constituents of igneous rocks
-have so great hardness. For example, if it is found that a rock is
-composed of orthoclase hornblende and quartz, and the texture is
-granitoid, it is granite: or if the rock is plagioclase feldspar and
-pyroxene of any sort, it is gabbro, etc.
-
-
-Granite
-Pl. 53
-
-The combination of orthoclase feldspar (or microcline), quartz, and
-either mica, hornblende or augite is termed granite, if the texture is
-coarse enough so the individual minerals can be recognized with the
-unaided eye. The rock is light-colored because the feldspar and quartz
-dominate. Accessory minerals may be present such as apatite, zircon,
-beryl or magnetite. Varieties of granite are distinguished according to
-the dark mineral present. When this is muscovite, it is a
-_muscovite-granite_; when it is biotite, a _biotite-granite_; if it is
-hornblende, a _hornblende-granite_; etc. The size of crystals in granite
-varies widely. When they are as small as ¹/₁₂ of an inch in diameter, it
-is termed fine grained; from ¹/₁₂ to ¼ of an inch, it is medium-grained;
-when larger, it is coarse-grained. In some cases the crystals may be
-over a foot in diameter which is known as _giant granite_.
-
-Originally granite was a great mass of molten magma, which has cooled
-very slowly, having been intruded or thrust up in great stocks or
-batholiths beneath overlying rocks, which acted as a blanket to prevent
-rapid cooling. These overlying rocks, in their turn, have been acted
-upon by the heat and metamorphosed. Granite is particularly likely to
-have been formed under mountain folds; so that, after the mountains have
-been more or less completely eroded away, the great masses of granite
-have come to the surface to mark the axes of the ranges; and even after
-the mountains have been wholly worn away, the granite remains to mark
-the sites on which they stood.
-
-In the granite mass itself, there are often veins and dikes, which
-probably resulted from the shrinkage of the cooling granite, and they
-are filled with a different and usually coarser granite known as
-pegmatite. This pegmatite formed from the residual magmatic material, so
-that as some of the elements had already crystallized out, the granite
-in these dikes is of different composition. The extreme coarseness of
-these pegmatites seems to be due to the character of the mineralizing
-agents left in the dikes. In some of these pegmatites the feldspar and
-quartz are so intergrown, that when broken along the cleavage surface of
-the feldspar, the quartz appears like cuneiform characters, and this
-variety has been given the name _graphic granite_ (See Plate 53).
-
-When granite is exposed to weathering, the feldspar is the first mineral
-to be decomposed, altering eventually into carbonates, quartz and
-kaolin. The dark minerals are only slightly less susceptible and they
-break down into carbonates, iron oxides and kaolin. The original quartz
-remains unchanged. Of these products the carbonates, some of the iron
-oxide and a little of the quartz are carried away in solution. The
-kaolin and some of the iron oxide is in fine particles and they are
-carried by the water until it comes to the lakes or the sea. The quartz
-is left in coarser grains, which are more slowly transported, and
-deposited in coarser or finer sand and gravel beds.
-
-Granites are widely used for building stone, because they can be worked
-readily in all directions, and have great strength and beauty. The color
-depends largely on the color of the feldspar, which may be white or
-pink, in which case the granite will be gray to pink.
-
-Granites occur throughout New England, the Piedmont Plateau, the Lake
-Superior Region, the Black Hills, Rocky Mountains, Sierra Nevada, etc.
-
-
-Syenite
-Pl. 54
-
-The combination of orthoclase and either mica, hornblende, or augite is
-syenite, the texture being coarse enough so that the individual minerals
-can be distinguished by the unaided eye. It differs from granite in the
-absence of quartz. Syenite is a light-colored rock with the feldspar
-predominating. Minerals like apatite, zircon, or magnetite may occur in
-it, as accessory minerals. The foregoing would be an ideal syenite, but
-usually there is some plagioclase feldspar also present. If this occurs
-in such quantities as to nearly equal the orthoclase feldspar, the rock
-is termed a _monzonite_; if it predominates, the rock becomes a diorite.
-The presence of quartz would make this rock into a granite. Such a
-compound rock has its type form, and when the proportions of the
-component minerals are changed, it grades into other types.
-
-Like the granite, syenite is an intrusive rock, which occurs in stocks
-and batholiths along the axes of present or past mountain ranges. The
-original magma welled up under the mountain folds, where it cooled
-slowly, metamorphosing the adjacent rocks. Like granite it has only been
-exposed after a long period of erosion has removed the overlying layers
-of rock.
-
-Syenites are not as abundant as granites, but they occur in the White
-Mountains, near Little Rock, Ark., in Custer Co., Colo., etc.
-
-
-Quartz-Diorite
-
-The combination of plagioclase feldspar, quartz and either mica or
-hornblende makes quartz-diorite, sometimes called _tonalite_. The above
-would be the typical quartz-diorite, but there is usually some
-orthoclase present, which if it equals the plagioclase feldspar in
-amount makes this into a monzonite; or if it dominates, it makes the
-rock a granite. Quartz-diorite is darker colored than the two preceding
-rocks, the dark minerals being about as abundant as the light-colored
-ones, such as feldspar and quartz. For this reason the weight is also
-somewhat greater.
-
-Like the others this is an intrusive rock, occurring in stocks and
-batholiths, and indicative of great molten masses thrust up under
-mountain folds, and only exposed after the overlying rocks have been
-weathered away. It is by no means an abundant type of rock, but occurs
-at Belchertown, Mass., Peekskill, N. Y., in the Yellowstone Park, etc.
-
-
-Diorite
-
-Plagioclase feldspar with hornblende or mica, or with both, is known as
-diorite. It is distinguished from quartz-diorite by the absence of
-quartz. There is generally some augite in it, but if this should be
-equal to, or exceed the hornblende, the rock is then a gabbro. There may
-also be a small amount of orthoclase present, without taking this rock
-out of the diorite class, but if the orthoclase feldspar becomes
-dominant, then the rock is a syenite. Thus there is gradation into other
-groups in all directions. Apatite, magnetite, zircon, and titanite often
-occur in small quantities as accessory minerals. Generally the
-hornblende is in excess of the feldspar, so that the rock is a
-dark-colored one.
-
-Diorites occur in much the same manner as granites, being in stocks,
-batholiths or dikes, and are often associated with granites and gabbros.
-They are great intruded masses, associated with mountain making, and
-like the preceding rocks, cooled far below the surface, and have been
-exposed only after great thicknesses of overlying rocks have been
-weathered away.
-
-Peekskill, N. Y., the Sudbury nickel district in Canada, Mt. Davidson
-above the Comstock Lode in Nevada, etc., are typical localities for
-finding diorite.
-
-
-Olivine-Gabbro
-
-The combination of plagioclase feldspar with augite (or any of the
-pyroxenes) and olivine makes olivine-gabbro. The feldspar is usually one
-of those with considerable calcium in it, like labradorite; and as the
-dark minerals predominate, the rock is dark-colored. It is an intrusive
-rock, usually in dikes or stocks, where it solidified far below the
-surface, and was only exposed after the overlying rocks were weathered
-off. It is by no means an abundant type of rock, but is found in the
-Lake Superior Region, and near Birch Lake, Minn.
-
-
-Gabbro
-Pl. 54
-
-Plagioclase feldspar with any one of the pyroxenes, most commonly
-augite, is gabbro. There is a wide range in the relative proportions of
-the two minerals making gabbro. At one extreme are rocks made entirely,
-or almost entirely, of plagioclase feldspar, which are known as
-anorthosites, and occur in parts of the higher mountains of the
-Adirondacks like Mt. Marcy, in several places in eastern Canada, etc.
-Then there are the typical gabbros where the feldspar and augite are
-more or less equally represented. At the other extreme come those
-gabbros in which the pyroxene predominates, in the most marked cases the
-feldspar being entirely lacking, and the rock being termed a pyroxenite.
-When the pyroxene of a gabbro is either enstatite or hyposthene (usually
-the latter) the gabbro is often called norite. Magnetite, biotite, and
-hornblende may occur in small quantities as accessory minerals.
-
-Gabbro is a common intrusive rock, occurring in stocks, batholiths, and
-dikes, and often varies considerably in different parts of the mass.
-Like granite the mass solidified far below the surface, under some
-mountain fold, and has only been exposed as the result of weathering
-away the layers of overlying rock. Gabbros appear much like diorites,
-but are distinguished by the fact that the dark mineral is one of the
-pyroxenes, instead of an amphibole or a mica. They are widely
-distributed, being found in the White Mountains, near Peekskill, N. Y.,
-Baltimore, Md., about Lake Superior, in Wyoming, the Rocky Mts., etc.
-
-
-Peridotite
-
-A rock made up of olivine and augite (or any of the pyroxenes) is
-peridotite. As it contains no feldspar, and both augite and olivine are
-dark-green to black in color, these rocks are always dark green to black
-in color and of considerable weight. They are usually rather coarsely
-crystalline. Peridotite is usually associated with gabbro, making dikes
-which lead from the main gabbro mass. Less frequently it occurs
-independently, making up an intrusive mass. Hornblende and mica may be
-present in small quantities, as accessory minerals.
-
-In general these are rather rare rocks, making dikes connected with
-stocks or batholiths of gabbro. Peridotite is found near Baltimore, Md.,
-in Custer Co., Colo., in Kentucky, etc.
-
-
-Pyroxenite
-
-This represents the extreme among coarsely crystalline igneous rocks, a
-whole mass made up of one mineral, and that some one of the pyroxene
-group. If the mineral can be exactly determined, the rock may be still
-more definitely named. For instance if it is all augite, then the rock
-would be called augitite. Like the preceding rocks, pyroxenite is an
-intrusive rock, usually found in dikes, which are connected with gabbro,
-and it represents the segregation of one mineral out of the gabbro, and
-its solidification at one point. Hornblende, magnetite and pyrrhotite
-may be present as accessory minerals. This is not a common rock, but it
-illustrates the fact that all possible combinations do occur, if the
-circumstances have warranted it. It is found near Baltimore, Md.,
-Webster, N. C., and in Montana.
-
-
-Rhyolite
-
-This is a combination of orthoclase feldspar, quartz, and either
-hornblende, mica or augite in which the crystals are of such small size
-that they can not be identified with the naked eye. In composition it
-corresponds to granite, but it is much finer in texture. It differs from
-trachite by having quartz while the latter has none. This can usually be
-determined by trying the hardness as none of the other minerals are as
-hard as 7. It is much harder to distinguish it from dacite which differs
-only in having plagioclase feldspar in place of the orthoclase, and only
-the microscope will enable one to make this distinction. Where the
-distinction cannot be made these light-colored lavas are often called
-felsite.
-
-Rhyolite is usually an extrusive lava, occurring in sheets, but
-sometimes it is intrusive, occurring in sills, dikes, and laccoliths. In
-all these cases the lava has solidified so rapidly, that the crystals
-are tiny, and only the general effect of a crystalline structure is
-distinguishable. Rhyolites may occur with porphyritic structure, in
-which case the presence of the larger feldspar crystals will help to
-distinguish whether they are orthoclase or not, making the determination
-easier. The color of rhyolites is green, red or gray, always a decided
-light shade.
-
-Rhyolites are abundant in the western states, as in the Black Hills, the
-Yellowstone Park, Colorado, Nevada, California, etc.
-
-
-Trachite
-
-The combination of orthoclase feldspar with mica, hornblende or augite
-is termed trachite, if the texture is dense. It is usually an extrusive
-lava of light color (green, red or gray), and corresponds in composition
-to syenite. It can be distinguished from rhyolite by having no quartz,
-and so nothing to show a hardness above 5.5; but it is difficult to
-distinguish it from andesite, which differs only in having plagioclase
-feldspar in place of orthoclase. It sometimes occurs with a porphyritic
-structure, in which case the feldspar crystals are usually large enough
-to be distinguished.
-
-Trachites are not abundant in America, but some are found in the Black
-Hills of South Dakota, in Custer Co., Colo., and in Montana.
-
-
-Dacite
-
-The union of plagioclase feldspar, quartz, and either hornblende or mica
-is termed dacite, if the texture is dense. It is an extrusive lava,
-occurring mostly in sheets and dikes. It corresponds in composition to
-quartz-diorite. As the texture is dense it is difficult to distinguish
-dacite from rhyolite, for both have quartz and differ only in the
-character of the feldspar, so it is quite common to use the term felsite
-which does not distinguish between the two, and only states that the
-rock is dense, light-colored and extrusive. When, as often occurs, the
-texture is porphyritic, and the feldspars are the large crystals, then
-exact determination is fairly easy.
-
-Dacites are rather common, occurring on McClelland Peak, Nev., in the
-Eureka district, Nev., on Lassen’s Peak, Calif., Sepulchre Mt. in the
-Yellowstone Park, etc.
-
-
-Andesite
-
-The union of plagioclase feldspar with mica, hornblende or augite, makes
-andesite if the texture is dense. The lack of quartz, and so no mineral
-which has a hardness of over 5.5, makes it possible to distinguish
-andesite from dacite or rhyolite, but it is hard to distinguish this
-rock from trachite, which differs only on having orthoclase feldspar in
-place of plagioclase. When the texture is porphyritic and the feldspars
-are the large crystals, then it is easy to make the distinction.
-Andesite gets its name from being the characteristic lava of the Andes
-Mountains, and is the commonest of all the extruded, light-colored
-lavas, being the lava of hundreds of flows throughout the western United
-States.
-
-The union of plagioclase feldspar and biotite is the commonest type.
-Plagioclase with hornblende or augite is less common, and, when they do
-occur, they are usually distinguished as _hornblende-andesite_ or
-_augite-andesite_. Magnetite, apatite and zircon may be present as
-accessory minerals.
-
-The lavas of Mt. Hood, Shasta, Rainier and others of the volcanic peaks
-of the Cascade Range, those at Eureka and Comstock in Nevada, in the
-Yellowstone National Park, and the porphyries of many peaks in Colorado,
-like the Henry Mts., etc., which are exposed laccolithic intrusions, are
-all andesites, as are many more.
-
-
-Basalt
-
-The combination of plagioclase feldspar with olivine and augite (or any
-other pyroxene) makes a heavy, dark-colored, black to dark-brown rock
-which, if its texture is dense or porphyritic, is termed basalt. This
-usually has more or less magnetite in it as an accessory mineral, indeed
-the magnetite may be so abundant as to be a component part of the rock.
-This magnetite makes trouble for anyone trying to use a compass on or
-about basalt rocks. These are extrusive or intrusive rocks and
-correspond in composition to gabbro.
-
-Basalts are among the commonest of igneous rocks, and are popularly
-designated “_trap_,” much used as a road ballast on account of its
-toughness, which is largely due to its dense texture. The coast of New
-England is seamed with dikes of basalt, and through the Adirondack and
-White Mountains there are a host of these dikes. The crests of such
-mountains, as the Holyoke Range, the Tom Range, the Talcott Mts., East
-and West Rocks at New Haven, etc., are all basalt sheets. The Palisades,
-First Wachung and Second Wachung Mountains of New Jersey are sills of
-basalt. The Lake Superior region is crisscrossed with basalt dikes. That
-greatest of all lava fields the Columbia Plateau, covering over 200,000
-square miles on the Snake and Columbia Rivers in Oregon, Washington and
-Idaho, is all basalt. So it goes all down through Nevada, New Mexico and
-California.
-
-
-Porphyry
-Pl. 55
-
-This is a term which properly refers to texture alone, indicating a
-lava, which has cooled in such a manner that one mineral has
-crystallized out of the magma first and developed to a larger size,
-while the mass of the material formed tiny crystals in which the larger
-ones are embedded. The large crystals are technically known as
-_phenocrysts_. The surrounding mass of tiny crystals is termed the
-_matrix_. This porphyritic structure is especially characteristic of
-lavas which have been extruded in large masses, and of intruded lavas in
-such places as sills and laccoliths.
-
-The term porphyry today has the above precise meaning. It is a much
-abused word, and has had all sorts of meanings. In the past it was first
-used to refer to lavas in general, then it came to be applied to lavas
-which had been erupted before Tertiary times, that is to all ancient
-lava sheets. This idea soon proved incorrect, lavas being of the same
-composition whether ancient or recent. In the West the word is often
-colloquially used today to designate almost every kind of igneous rock
-occurring in sheets or dikes, if in any way connected with ore deposits.
-
-When the composition of a rock with porphyritic textures can be
-determined, the name due to the composition is coupled with that due to
-texture, making such terms as _trachite-porphyry_, _basalt-porphyry_,
-etc.
-
-
-Tuff
-
-Tuff, a term not to be confused with tufa on page 215, is the name used
-to designate the finer fragmental ejecta of volcanic eruptions, which
-are also often referred to as “volcanic ash,” but the word, ash, conveys
-the false impression that the rock is a remnant of something burned, and
-is therefore not a good term. When first ejected, tuff is loose
-material, but it is usually soon cemented to make a more or less firm
-mass of rock, for which the term, tuff, is still retained. In some
-cases, while still loose, it is carried by streams to a distance and
-deposited in more or less sorted and layered beds: and the finer tuff is
-often carried by the winds and laid down, at a considerable distance
-from its source, in so called “ash beds.” In both these cases,
-sedimentary characteristics have been added to the tuff, and layering
-which is characteristic of sedimentary deposits, is present. These
-transported tuff beds are really sedimentary, but as there is little
-change in the material, they are referred to here and not again. These
-tuff beds are not at all uncommon in the sedimentary deposits of
-Tertiary age in the Rocky Mountain region. The coarser material of
-volcanic eruptions usually goes under the head of breccia.
-
-
-Breccia
-
-This term is used to describe the coarse fragmental ejecta of volcanic
-eruptions. It is also used, in the section under sedimentary rocks, in a
-broad sense to include all angular unworn fragmental material, whether
-of igneous or sedimentary origin. For this reason, when dealing with
-igneous rocks, it is usual to designate the fragments according to their
-composition, making such terms as _trachite-breccia_,
-_rhyolite-breccia_, etc.
-
-While still loose (and also even when cemented into beds of rock), it is
-customary to designate the smaller fragments, from the size of a grain
-of wheat up to an inch or two in diameter, as _lapilli_; the larger
-fragments, from two inches up to a foot or so in diameter, as _bombs_;
-and the largest masses, often tons in weight, as _volcanic blocks_.
-
-
-Obsidian
-Pl. 55
-
-Lavas, which have cooled so quickly that crystals have not had time to
-form, have a glassy appearance, and are termed obsidian. If the color is
-dark, due to the presence of large amounts of those elements which make
-dark minerals, this lava is termed _basalt-obsidian_. Obsidian is
-characterized by its glassy texture, a hardness around 6, and by
-breaking with a conchoidal fracture, so called because the surface is
-marked by a series of concentric ridges, something like the lines of
-growth on a shell. Obsidians vary greatly in color, but are usually red
-or green to black, and translucent on thin edges. While glassy, all the
-obsidians contain embryonic crystals, which appear like dust particles
-floating in the glassy matrix, or there may even be a few larger
-crystals present, which are often arranged in flow lines. Most all large
-masses of obsidian have streaks or layers of stony material in them
-where crystallization has set in, in a limited way.
-
-Near the upper surface, obsidians usually have gas cavities scattered
-through them, and these may be small and few, or large and numerous.
-Indeed the cavities may be so numerous as to dominate and give the rock
-a frothy appearance. In this case, if the cavities are small and more or
-less uniform, the rock is called _pumice_; if they are larger it is
-_scoria_. If, as often happens when the lava is ancient and has been
-buried beneath other rocks, the cavities have been filled with some
-secondary mineral, then the lava is called an _amygdoloid_.
-
-Obsidian is found in many localities, especially where there are recent
-volcanoes, the most famous places being the obsidian cliffs in the
-Yellowstone Park, those near Mono Lake in California, and many other
-localities in the Rocky Mountains, the Sierra Nevadas, and the Cascade
-Mountains.
-
-
-Pitchstone
-
-This is very like obsidian in appearance, but differs in that the glassy
-material contains from five to ten per cent of water in its composition,
-the most obvious effect of which is to make the luster resinous, instead
-of vitreous, as is characteristic of obsidian. The colors are commonly
-red, green or brown. Pitchstone is associated with recent volcanoes, and
-some fine specimens have come from Silver Cliffs, Colo., and various
-parts of New Mexico and Nevada.
-
-
-Perlite
-_pearlstone_
-
-Perlite is a glassy lava, containing two to four per cent of water,
-which, on cooling, has cracked into numerous rounded masses, with a
-concentric structure, reminding one of the layers of an onion.
-
-
-Scoria
-
-While lava is cooling, there is a constant escape of gases, mostly
-steam, and as these rise through the molten mass they make cavities,
-near the upper surface, that portion on top often becoming frothy. If
-this solidifies quickly so that the gas cavities are preserved it is
-scoria. When the gas cavities are small and uniformly distributed, the
-rock is called pumice, and often used as a scouring agent. When the
-cavities are large and irregular the term scoria is generally used.
-Molten lavas may form various structures, according to the conditions
-under which they cool, dripping through cracks or from the roof of
-caves, which often form where the molten lava escapes from a hardened
-shell, and making stalactites, stalagmites, etc. The very thin lava of
-the Hawaiian volcanoes may even be blown by the wind into fine threads,
-known as “Pele’s hair.”
-
-The presence of the gas cavities is so characteristic of the upper
-surface of lavas which have been extruded; that, where one is dealing
-with older lavas, now buried beneath other rocks, this fact helps to
-determine whether the mass is a sheet, rather than a sill; for, in the
-case of the sill, the lava was forced between layers of sedimentary
-rocks, and the burden of the overlying rocks did not permit the escape
-of steam and therefore the upper surface of sills does not have the
-scoriaceous structure.
-
-
-Amygdoloid
-Pl. 56
-
-When the upper surface of a lava is filled with steam holes, and this
-lava has been buried beneath other rocks, the seeping waters slowly
-bring such minerals as quartz, calcite and zeolites and fill the
-cavities. Such a rock is known as an amygdoloid. It is often confused
-with porphyry; but, if examined closely, it will be seen that the
-outlines of the gas cavities are rounded, while the outlines of a
-crystal, like a phenocryst, are always angular. This will be clear if
-the amygdoloid on Plate 56 is compared with the porphyry on Plate 55.
-
-
-                         The Sedimentary Rocks
-
-To this class belong all those rocks which have been laid down by water
-or wind, or are the results of organic depositions. They include loose
-material like sand or day, and also the same materials, when cemented
-into more or less solid rocks, like sandstone or shale. So long as the
-material has not been altered from what it was when laid down, the rock
-is termed sedimentary.
-
-In general the material of which these rocks are composed comes from the
-weathering and disintegration of other rocks. This does not apply to the
-organic deposits, for each type of which there is a peculiar mode of
-formation. To illustrate the typical formation of sedimentary rocks, we
-may look at the fate of a granite when exposed. At once the surface is
-attacked by changes of temperature, frost and rain. The various minerals
-of the granite expand and contract with every change of temperature, but
-each component mineral has a different coefficient of expansion under
-heat, so that minute cracks are quickly formed between the minerals.
-Water gets into these cracks and begins to dissolve the minerals.
-Feldspar is the most easily attacked, part of it being dissolved and
-carried away, a small part changing to quartz, and by far the largest
-part changing to kaolin. The dark mineral is also attacked and partly
-dissolved, and partly changed to kaolin and iron oxides. The quartz
-resists solution almost completely. Of these products the kaolin and
-iron oxides are carried far away and deposited in still water. The
-quartz and perhaps some of the dark mineral are heavier and carried more
-slowly, being deposited as sand. This happens to granite everywhere, but
-in the regions where there is frost the action is greatly hastened; for
-water gets into the cracks and expands every time it freezes and thus
-widens the cracks rapidly, which greatly facilitates the entrance and
-movement of water in the rock. In a similar way any original rock will
-be disintegrated, and the residue, after the soluble part has been
-carried away, becomes sand or clay or mud.
-
-Particles of quartz, kaolin, and lime, separately, or mixed, loose or
-more or less cemented, with accompanying impurities, make up the great
-bulk of the sedimentary rocks. They are usually arranged in layers, of
-varying thickness, as they were laid down by water or the wind. In the
-same way layered accumulations which are either products of plants or
-animals, or parts of the plants or animals, are considered sedimentary,
-as for instance, coal, chalk, petroleum, etc.
-
-
-                 A Classification of Sedimentary Rocks
-
-  Inorganic origin:
-    1.  Coarse fragmentary material          talus
-        resulting from weathering
-    2.  The same fragmentary material        breccia
-        cemented
-    3.  Unsorted material resulting from     soil
-        rock weathering
-    4.  Coarse fragments rounded by the      gravel
-        action of water and wind
-    5.  The same material cemented           conglomerate
-    6.  Finer material deposited by water    sand
-        or wind
-    7.  The same material cemented           sandstone
-    8.  The finest material, mostly          clay
-        kaolin, deposited by water
-    9.  The finest material, deposited by    loess
-        wind
-   10.  The same material cemented           shale
-   11.  Fine particles of lime, pure or      marl
-        impure
-   12.  The same material cemented           limestone
-   13.  Unassorted material left by the      till
-        glacial ice
-   14.  The same material cemented           tillite
-  Organic Origin:
-   15.  Limes made from shells, etc.         coquina, chalk, coral rock,
-                                             etc.
-   16.  Silica from the shells of plants,    diatomaceous earth, etc.
-        etc.
-   17.  Carbon from plants                   peat, lignite, coal, etc.
-   18.  Hydrocarbons from animals            petroleum, asphalt, amber,
-                                             etc.
-   19.  Phosphates from animals              guano, phosphate rock, etc.
-
-
-Talus
-
-Where weathering is very active, especially on or below steep mountain
-slopes, a mass of loose, angular fragments accumulates. This material is
-termed talus, a term which refers only to the physical character of the
-material, and not at all to its composition. If weathering continues
-these fragments will be further broken up into one of the finer grained
-rocks, which the water can carry away and deposit elsewhere. There is
-little or no layering in talus. If the talus is not carried away but is
-cemented where it was formed, the resulting mass is termed breccia, but
-this is not very commonly the case.
-
-
-Breccia
-Pl. 58
-
-The term breccia is used to cover all those rocks which are composed of
-angular fragments, of any composition, and above sand in size, when they
-are cemented into a solid mass, by any sort of cementing agent. Here the
-term is used in its broad sense, as compared with the way it was used
-under igneous rocks.
-
-Breccias may result from the cementing of talus, but more often the
-breaking up of the material into angular fragments was due to other
-causes, such as crushing along a fault plane, or in the movements
-involved in mountain making. In such cases the breccia is of limited
-extent, but may occur repeatedly in the same neighborhood. Limestone,
-which has been crushed and then recemented, often makes a rock which
-takes a good polish and is used in several localities as an ornamental
-stone in place of marble, in fact often goes in trade circles under the
-name of “marble.” The breccia figured on Plate 58 is such a limestone.
-
-
-Soil
-
-Over most of the earth’s surface there is a covering of rock waste, the
-product of weathering, some of which is unassorted, and some of it
-sorted by water or wind. This is all termed soil. It is an ever-moving
-cover resulting from the decomposition of the underlying rocks, to which
-have been added in places layers of rock waste brought from afar by the
-streams. Some soils are rock waste which had been carried clear to the
-ocean and deposited on the floor of the sea, and is now above sea level,
-because the floor of the sea has been elevated. Inasmuch as the
-underlying rocks vary in composition, and as there are areas of
-transported material, it is clear that the composition of soils must
-vary from place to place, both as to composition and texture.
-
-Soils range from the finest, composed mostly of clay, to coarse ones,
-composed of sand, gravel or even boulders. Clay, the finest grained
-soil, is composed of particles only about ¹/₁₀₀₀th of a millimeter in
-diameter, of which it would take 720,000 billion particles to make a
-gram’s weight. Ordinary soils however have about 2 to 5 million
-particles to the gram.
-
-The average specific gravity of soil with the usual amount of humus in
-it is from 2.55 to 2.75. In this case however the specific gravity is of
-less importance than is the volume weight. A cubic foot of water weighs
-62½ pounds, that of soil from 75 to 80 pounds, the extremes being 30 lb.
-for peaty soil and 110 lb. for calcareous sand. The terms “heavy” and
-“light,” used in agriculture do not refer to the volume weight, for clay
-which is actually relatively light (70-75 lb. per cubic foot) is classed
-as a “heavy” soil; while sand, of much greater actual weight, is classed
-as a “light” soil. These terms as used in agriculture refer to the ease
-with which the soils are worked, and to their penetrability by plant
-roots.
-
-Soil is usually divided into an upper darker-colored layer, termed loam,
-and into a lower, lighter-colored layer, termed subsoil. The presence of
-humus, resulting from the decomposition of plant and animal remains is
-the factor which darkens the color and distinguishes the loam; so that
-loam is a complex of inorganic rock particles plus more or less humus,
-colloid compounds, bacteria, living plants and animals. The subsoil is
-mainly rock particles. The distinctions between these two layers break
-down in arid soils, and often also in swampy regions.
-
-It is this layer of soil on which the water of every rain and flood
-works, picking part of it up and carrying it along, step by step, to the
-sea. Though the amount moved on any one day is small, the sum of all the
-soil transported is enormous, a large river carrying annual incredible
-amounts. For instance the Mississippi annually deposits in the Gulf of
-Mexico 476,900,000 metric tons (2204 lb. to the metric ton), of which
-about a third is in solution. At this rate it takes about 7000 to 9000
-years to remove a foot from over the whole drainage basin. This is
-considerably slower than is the case of some other rivers. While on the
-one hand soil is being continuously carried away from the surface, on
-the other hand it is being constantly renewed from below, by the
-weathering action of water, air and temperature.
-
-
-Gravel
-
-Gravel is a mass of loose fragments of rock, which have been rounded by
-water and deposited with little or no sorting, so that larger and
-smaller pebbles and sand all occur together. It is the deposit laid down
-by comparatively fast water in inland lakes or along the storm-beaten
-shores of the sea. Where a swift stream enters quiet water, as where it
-empties into a lake, there it quickly drops its coarse material as
-gravel, usually thus building a delta. Gravel also occurs in stream
-beds, where for any reason the rate of flow is checked. During the
-recent glacial period, the ice sheet brought down great masses of
-unsorted material, which was deposited as till, or in moraines. Much of
-this was then picked up by the running water and moved longer or shorter
-distances, so that, all over the glaciated country of the northern and
-eastern United States, there are unusually large numbers of gravel
-deposits. Gravels are all water laid, and usually show more or less
-clearly the bedded or stratified structure.
-
-The size of the component pebbles of gravel ranges from great boulders
-to fine sand, and the finer gravels grade into the coarser sands, the
-line between gravel and sand being drawn at about the size of a pea, the
-coarser being gravel, the finer sand.
-
-Gravel is widely used as ballast for railroads and in making highways,
-because of its tendence to pack well, while the hard pebbles resist
-wear. It is also widely used in concrete work, bonding in well with the
-cement, and making it go from three to five times as far.
-
-
-Conglomerate
-Pl. 58
-
-Conglomerates are composed of rounded pebbles and sand of varying sizes,
-cemented together into a solid rock. The pebbles may run up to boulders
-in size, but they have all been more or less rounded by water, and
-transported some distance. The pebbles may all be of the same
-composition, or may represent a variety of rocks. When the pebbles are
-all, or most all, of one sort, the resulting conglomerate is termed a
-_quartz-conglomerate_, a _limestone-conglomerate_, a
-_gneiss-conglomerate_, etc. So too the cementing material varies in
-kind, silica, calcite and iron oxide being the commonest. The color will
-depend on both the component pebbles and the cement, sometimes one
-dominating, sometimes the other. There are some of the quartz- and
-limestone-conglomerates which can be cut and polished to make very
-handsome stone.
-
-Conglomerates represent consolidated gravels, and always indicate an
-aqueous origin, quite often the delta of an ancient stream, or the
-invasion of the sea over the land; so they have become of importance to
-geologists in interpreting past events.
-
-
-Sand
-
-Sand is a mass of small rock particles, from the size of a pea down to
-¹/₅₀₀ of an inch in diameter. The material may be any sort of rock, or a
-mixture of two or more kinds. Sand may be the result of the
-disintegration of older rocks at the point where it is now found, in
-which case the grains have the shapes they had in the original rock; but
-more often the sand grains have been transported greater or lesser
-distances, and in the process have been more or less rounded.
-
-Those sands, which lie where they were formed are called _residual_, and
-such sand is usually composed of a mixture of angular grains, some
-harder and others softer, such as quartz, feldspar, mica and hornblende,
-all mixed together. Where the sand has been transported, only the more
-resistant minerals have remained, such as quartz, magnetite,
-cassiderite, etc.; with which there are at times rarer minerals, such as
-gold, platinum, garnets or topaz. Such sands are known as
-_gold-bearing_, _topaz-bearing_, etc.
-
-The sands from different localities differ greatly. The streams gather
-the rock particles, and sort them according to the size, which the water
-flowing at any given rate can carry. When the water is slowed down, it
-drops all the particles above the size which the new rate of speed can
-handle. The grains of sand from the bed of a stream are usually more or
-less angular. The further they are carried, the more they are knocked
-together and rounded; so that after being carried to the sea, and then
-thrown up on the beaches, they have been well rounded, especially the
-larger grains. As the air is less viscid than the water, sand which is
-transported by the wind, is even more rounded; so that desert sands show
-the most complete rounding, indeed are even polished; and this is true
-even of the smaller grains. It is the wind-blown, or desert sands, which
-flow so evenly in an hourglass. Between the angular residual sands and
-the polished desert sands, there are of course all grades. Glacial sands
-are angular or “sharp” almost to the degree characteristic of residual
-sands; and lake-shore sands are between river sands and sea sands in the
-degree of rounding.
-
-Sands made of particles of lime, _calcareous sands_, are less resistant
-to wear than are those of quartz. In regions where the water is “soft”
-(free from lime), they do not last long, as they are dissolved; but in a
-limestone region where the water is “hard” (saturated with lime), the
-grains are not so quickly dissolved and may accumulate into beds of
-great thickness, as in Florida. Along some shores of the ocean, there
-occur “green sands,” which are ordinary quartz sands mixed with the dark
-green mineral glauconite, which is a potassium iron silicate, forming on
-the ocean bottom as a result of the action of decaying animal matter on
-iron-bearing clays and potassium-bearing silicates, like feldspar. This
-is particularly characteristic of some of the sands along the coast of
-New Jersey.
-
-In places, especially in the beds of rivers, there occur “quicksands.”
-This is a deposit of fine sand, mixed with a considerable amount of
-clay, and saturated with water; so that it will not support the weight
-of a man or an animal. Much that goes under the name of quicksand is a
-fluid mud, covered with a thin layer of sand.
-
-Sand is used for a wide variety of commercial purposes, and under these
-conditions gets various trade names; for instance “glass sand” is a
-pure, colorless to white, quartz sand, which is used as one of the
-components in making glass. It must be free from impurities, as these
-color the glass, and much of the sand used for this purpose is quartz,
-crushed to a fine sand-like condition. “Moulding sand” is a rather
-fine-grained quartz sand, with a small but very definite admixture of
-clay, and this is used to make the moulds for castings in foundries.
-“Polishing sand” is one composed of angular fragments of quartz, usually
-from stream beds or glacial deposits, or even crushed quartz, and is
-used for cutting and polishing marble, for sandpaper, and for polishing
-wood and softer stones. There are many other special uses, like
-building, ballast, filters, furnaces, etc., in which quartz sand is
-used, being screened if necessary to get the right sizes.
-
-
-Sandstone
-
-When sand of any sort is cemented so as to make a solid rock, it is
-termed sandstone, which varies widely according to the size, color and
-composition of the grains, and also with the sort and amount of the
-cement. When the size of the grains is larger than that of a pea,
-sandstone grades into conglomerate; when smaller than ¹/₅₀₀th of an
-inch, especially if mixed with clay, it grades into shale. There are all
-grades of firmness, due to the amount and kind of cement, ranging from
-those which have little or no cement, but are compact as a result of the
-pressure of the overlying rocks, to those in which the cement has filled
-all the pore spaces. In general there is a considerable amount of space
-between the grains of sand; so that a sandstone will absorb large
-amounts of water, up to 25% of its bulk. In moist climates where it
-freezes, this makes many sandstones unsuitable for use as building
-stones, as they are likely to spale, or chip off, as is seen in the
-“brown stone” so much used in New York City.
-
-Sandstones are usually bedded rocks and are relatively easy to quarry,
-and most of them are not so firmly cemented, but that they can be
-readily worked or cut into shape by the stone cutter; and so, certain
-sandstones are very popular for building stone or for trimming on
-buildings, where they are not too much exposed to the weather.
-
-Sandstone gets a variety of names according to the cement.
-
-Siliceous sandstone is cemented with silica and usually very hard.
-
-Calcareous sandstone is cemented with lime and usually rather soft.
-
-Ferruginous sandstone is cemented with one of the iron oxides.
-
-Argillaceous sandstone is held together with clay impurities, and is
-usually both soft and of undesirable color.
-
-According to their composition there is also a number of varieties.
-
-Arkose is a sandstone composed of quartz and feldspar grains, usually
-derived from the disintegration of granite and not transported far.
-
-Graywacke is a sandstone composed of quartz, feldspar, and some other
-mineral, like hornblende-augite, etc., also derived from the
-disintegration of granites and not transported far.
-
-Grit is a term applied to a coarse sandstone, composed of angular quartz
-fragments, and used to a considerable extent for millstones.
-
-Flagstone is a thin bedded sandstone, often with mica, which splits
-easily and uniformly along the bedding planes; so that it can be
-quarried in large slabs. It was widely used for sidewalks before the
-advent of concrete.
-
-Freestone is a thick-bedded sandstone, not over hard, so called, because
-it can be worked freely and equally well in all directions.
-
-
-Clay
-
-Clay is a term used to describe a mass of fine particles, the most
-prominent property of which is plasticity when wet. Clays range from
-masses of pure kaolin to masses of kaolin and related minerals mixed
-with as much as 60% of impurities, which may be sand, lime, iron oxides,
-etc. The particles of a fine clay range around ¹/₁₀₀₀ of a millimeter in
-diameter, while the impurities may be, and usually are, of larger size,
-up to the size of sand grains.
-
-All clays are of secondary origin, the result of weathering, especially
-of feldspars, though clays may also result from the weathering of
-serpentines, gabbros, etc. In some cases after the weathering of
-feldspar or limestones, the clay may remain just where it was formed, as
-a residual deposit; but, being so fine-grained, it is usually
-transported by rain water or by the wind and deposited somewhere else as
-a sedimentary bed. The quiet waters of a lake are favorable places for
-such deposits, and many clay beds represent former lake bottoms. Impure
-clays are often laid down on the flood plains of sluggish streams. In
-fresh water the settling of the clay is a very slow process, requiring
-days, or when very fine, weeks, before the water wholly clears. In salt
-water, however, the clay sort of coagulates, the particles gathering
-together in tiny balls, which settle rapidly, so that the water is soon
-clear.
-
-According to their mode of origin clays are classified as residual,
-sedimentary, marine, swamp, lake, flood-plain, eolian, etc. But when
-their uses are considered a very different classification is made, based
-mostly on their composition, and we speak of China clays or kaolins,
-fire or refractory clays, paving-brick clays, sewer-pipe, stone-ware,
-brick, gumbo and slip clays.
-
-The kaolin or china clays are residual clays, usually resulting from the
-decomposition of pegmatite dikes. They must be white when burned, free
-from iron oxides, and fairly plastic. A good deal of china clay is made
-by crushing feldspar.
-
-Ball clays are sedimentary clays which remain white when burned, are
-usually very plastic, and free from iron oxides. They are mostly used in
-the making of various sorts of china.
-
-Fire clays may or may not have iron oxides in them, but they must be
-free or nearly free from fluxing materials, such as lime, magnesia and
-the alkalies (sodium and potassium compounds). They may be more or less
-plastic, the essential quality being their ability to withstand high
-temperatures without fusing. Silica (as sand) tends to diminish the
-refractory quality; so that a clay otherwise suitable, if it has sand in
-it, becomes at best a second grade fire clay. In coal mining sections it
-is customary to term those beds of clay either above or below the coal,
-“fire clay”; but this is an unfortunate designation, for though some of
-them are true fire clays, the most of them are not.
-
-Stone-ware clays are those with considerable sand and up to five per
-cent of fluxing materials. They must be plastic enough to be readily
-worked, and then burn to a dense body at comparatively low temperatures.
-
-Sewer-pipe clays must be plastic, and carry a considerable amount of
-fluxing material, as the surface of the pipe is expected to vitrify in
-the burning.
-
-Brick clays are low grade clays and vary greatly in composition. The
-main requisites are that they mould easily and bake hard at relatively
-low temperatures with as little warping and cracking as possible. As
-most clays shrink both in the air drying and in the baking, sand is
-added when the clay is being mixed. The color is mostly due to the
-presence of iron impurities. If there are iron oxides and little or no
-lime, the brick bakes to a red color, but if there is an excess of lime
-over the iron oxides, it bakes to a cream or buff color, which on
-vitrifying turns green.
-
-Paving-brick clays range from surface clays, to semirefractory clays,
-shale being often used. The essential component is enough fluxing
-material, so that the bricks shall begin to vitrify, or fuse, at not too
-high temperatures.
-
-Slip clays are those with a high percentage of fluxing material; so
-that, when baked at moderate temperatures, the surface fuses into a
-glassy brown or green glaze.
-
-Adobe is an impure calcareous clay, widely used in the western United
-States for making sun-dried bricks.
-
-Gumbo is a term applied to fine-grained plastic clays which shrink too
-much in the burning to be useful in manufactures. They can be burned to
-make an excellent ballast for railroads and highways. They are
-especially abundant in the Middle Western States.
-
-
-Loess
-
-This is the name given to a fine grained homogeneous clay-like material,
-which is a mixture of clay, fine angular fragments of sand, flakes of
-mica and more or less calcareous matter. It is usually without
-stratification, and cleaves vertically, so that, when eroded, it forms
-steep cliffs. Loess covers great areas in the Mississippi Valley, in the
-Rhine Valley, and in North Central China. By some it is thought to be an
-accumulation of dust in those regions where the prevailing winds were of
-diminished velocity and where the grass or other vegetation has served
-to catch and hold the material; by others it is thought of as a river
-and lake deposit; and by still others it is thought to be due to the
-combination of the two modes, wind and flood. The writer inclines to the
-first view expressed.
-
-
-Shale
-Pl. 59
-
-When pure or impure clays, or loess, are consolidated, they are all
-grouped under the name shale. It usually possesses a layered or
-stratified structure, which makes it possible to split it into thin
-layers. Of all the sedimentary rocks shale is the commonest, and it may
-occur in all the places where clay could occur, but the most widely
-distributed shale is that which made the sea bottom of former times and
-is more or less calcareous, like the piece on Plate 59, in which bits of
-shells are still visible. Shale has the same wide variation in
-composition as has clay, the various types being designated according to
-the impurity which is present, as:
-
-_argillaceous shale_, made mostly of clay,
-
-_arenaceous shale_, shale with more or less sand as an impurity,
-
-_calcareous shale_, or one with more or less lime as an impurity,
-
-_ferruginous shale_, or one with iron compounds as impurities,
-
-_bituminous shale_, or one colored black by the presence of organic
-matter, remains of either plants or animals.
-
-While of no value as building material, shale may be ground or crushed,
-and used as a substitute for any corresponding clay, and thus many
-manufacturers use shale in making fire-clay products, bricks, tile, etc.
-
-
-Marl
-
-Where limestones or shells of any sort have been pulverized, and mixed
-with more or less impurities, especially clay, the resulting
-unconsolidated mass is known as marl. It is usually associated with
-marine formations, and is the finer débris which has settled on the
-ocean bottom well out from shore, that is out beyond the sandy and mud
-deposits. Finding it therefore usually indicates a sea bottom recently
-elevated. It is very characteristic of the southern coastal states, from
-Maryland all along to Texas.
-
-
-Limestone
-
-Any mass of marl, or aggregate of calcareous shells, corals, etc., which
-has become consolidated is known as limestone. It may, and usually does,
-have a wide range of impurities, chief of which are clay, sand, iron
-oxides, and bituminous matter, like plant or animal remains. Pure
-limestone is white, but due to impurities it ranges through grays,
-greens, browns, to black, and even red, but this last is rarer. It is
-easily identified by the presence of calcium carbonate, which
-effervesces in hydrochloric acid. It most often represents deposits in
-fairly deep water on ocean bottoms of the past, but there is also a wide
-range of limestones which were formed in fresh water.
-
-Limestone is often burned at temperatures just above 900° C, at which
-point carbon dioxide goes off as a gas, and leaves calcium oxide, or
-lime. When this is mixed with water it makes calcium hydroxide, or
-slaked lime, which is mixed with sand to give it body, and is used as
-mortar. When exposed to the air, the slaked lime gives up water, and
-takes back from the air carbon dioxide, and again becomes calcium
-carbonate with its original hardness. Limestone is also used as one of
-the elements in all cements. It is also considerably used as a building
-stone, which, however, suffers in moist climates from the solution of
-its lime by rains, but has stood up very well in dry climates.
-
-The varieties of limestone are mostly distinguished according to their
-mode of origin, some of them being as follows.
-
-Bog Lime is a white calcareous powdery deposit on the bottom of ponds in
-limestone regions, a deposit precipitated from solution by the action of
-the plants inhabiting the ponds.
-
-Coquina (Plate 59) is the rock formed by the rather loose consolidation
-of shells and shell fragments. It is particularly characteristic of
-tropical regions, and is very abundant near St. Augustine, Fla., in
-which region it was, and still is, cut into blocks and used for building
-stone. In that mild climate it has stood very well.
-
-Chalk (Plate 60) is a soft fine-grained limestone, formed in the ocean
-by the accumulation of myriads of the tiny shells of Foramenifera, which
-are single celled animals, living either a floating life near the
-surface of the sea, or a creeping life on the bottom. Chalk is composed
-mostly of the shells of floating Foramenifera, which when the animals
-died, settled to the bottom and there accumulated, mostly at depths of
-600 feet or more. When the mass of unconsolidated shells is dredged up
-from depths of 50 to 2000 fathoms, it is known as _Foramenifera ooze_.
-Chalk beds are then indications of an uplifted sea bottom. When
-consolidated, if pure or nearly so, it makes a white chalk, and the beds
-may be of considerable thickness, as is the case of the famous cliffs
-near Dover on either side of the English Channel. One of Huxley’s most
-famous lectures is the one on chalk, found in his _Essays and Lay
-Sermons_.
-
-Coral Rock is made by the cementation of fragments of corals. The
-binding material, as in most stones, is lime; and this sort of rock is
-associated with coral reefs of either the past or the present. One of
-the best illustrations of this being the “Dolomite Mountains” in Tyrol.
-Coral rock, like coquina, has been cut into blocks and used as building
-stone, as in Bermuda.
-
-Encrinal Limestone (Plate 60) is a rock made by the cementation of
-fragments of the skeleton of crinoids. These animals belong to the
-group, echinoderms, and are now extinct except for a few so called
-“sea-lilies.” They were animals with a central mouth surrounded by long,
-jointed, flexible arms in multiples of five, and below this a small body
-inclosed in calcareous plates, all at the top of a long jointed stem.
-They lived in the sea and in the earlier geological times must have been
-very abundant; for their remains are so common in places as to make
-whole layers of limestone.
-
-Hydraulic Limestone is a fine-grained, compact, yellowish limestone with
-from 13 to 17% of sand, and some clay; which, when it is burned at a
-temperature a little higher than that used in burning lime, makes a
-product, that, while not as strong as Portland cement, still like it
-sets under water.
-
-Lithographic Limestone is a very fine-grained, compact limestone with
-clay impurities, the finest of the grain making it usable for making the
-stone plates used in lithographic printing. On slabs of this limestone
-figures are drawn in reverse with a special crayon. Then the slab is
-treated with acid, those parts which are not protected by the drawing
-being etched away, while the points protected by the drawing remain in
-low relief. From this slab figures can then be printed.
-
-Travertine is a general name, applied to calcareous deposits from fresh
-water lakes or streams, and has been precipitated either as a result of
-cooling or evaporation. Some travertines are porous, while others are
-dense; some are white, while others are colored, often beautifully, by
-impurities in the water.
-
-Porous deposits of travertine, when made on grass or other like
-substances, are known as tufa or _calc sinter_. Such masses are common
-around Caledonia, N. Y., Mammoth Hot Springs in the Yellowstone Park,
-etc.
-
-Onyx marble is a dense travertine, usually formed as a result of the
-deposition of lime from the water of springs. It is often banded, due to
-the presence of impurities in the water at one time, and their absence
-at other times.
-
-
-Till
-
-Till is an unconsolidated mass of boulders, pebbles, sand and fine clay,
-the unsorted material left behind by glaciers when they melted. The
-boulders and pebbles, while they show some wear, are not rounded like
-those that have been transported by streams, but have a more or less
-angular shape; and some of them are polished or striated on one side,
-where, while frozen in the ice, they were rubbed along the bottom.
-
-One of the most recent geological events in America was the extension of
-the ice sheet, now covering Greenland, down over north and northeastern
-North America, until it extended as far south as northern New Jersey,
-the Ohio River and the Missouri River, and as far west as the Rocky
-Mountains, but not over the Great Basin, the Cascade Ranges or Alaska.
-This great mass of ice, thousands of feet thick, moved from two centers,
-one either side of Hudson Bay, scraping up the loose soil, and grinding
-off the exposed surfaces of the underlying rock. All this material it
-carried southward, until the melting along its lower margin equaled the
-rate at which it advanced. When the melting was faster than the advance
-the glacial sheet retreated. At the southern limit of the advance this
-débris was dropped, either making long ridges (moraines) or while the
-ice was retreating, thicker or thinner sheets. This deposited débris is
-till.
-
-The soil, and especially the subsoil, in all the regions formerly
-covered by the ice sheet, is made up very largely of this till; which,
-where it is undisturbed is often called “hardpan.” When till is mixed
-with humus it becomes loam. This mixture of material, varying all the
-way from the fine powdered products of the ice grinding to the great
-boulder it picked up and carried south, is characteristic of this or any
-other glaciated country. When this section of country was settled, the
-boulders and stone were a hindrance to cultivation, and were picked up
-and piled into stone walls, which are one of the first features to
-strike the eye.
-
-
-Tillite
-
-When till is consolidated into solid rock, it is known as tillite. In
-several cases it has been found buried far beneath the more recent
-sedimentary rocks; testifying that there were other glacial periods
-beside the last one which furnished the till.
-
-
-                            The Coal Series
-
-Disregarding minor constituents, the plants are largely made up of
-cellulose, which is a combination of carbon, hydrogen, and oxygen,
-(C₆H₁₀O₅). If this is heated in the air, where there is plenty of
-oxygen, it disintegrates, or burns, making carbon dioxide and water; but
-if the heating is done where the oxygen is excluded, as in a kiln, the
-hydrogen and oxygen will be driven off and the carbon will remain behind
-as charcoal. In Nature similar reactions go on, but more slowly.
-Vegetable matter, exposed to the air, disintegrates into carbon dioxide
-and water, and there is no solid residue. However, if the vegetable
-matter is under water, which excludes the air more or less completely
-including the oxygen in it, then disintegration still takes place, but
-the products formed are water, (H₂O) marsh gas (CH₄), and some carbon
-dioxide (CO₂), but a considerable part of the carbon remains behind and
-accumulates.
-
-Thus in bogs, swamps and ponds, where dead vegetation, especially that
-growing in the water, piles up, the oxidation is incomplete; so that
-there gradually accumulates on the bottom a layer of brown to black mud,
-known as _peat_. More plant remains are constantly being added, and the
-layer may increase to several feet in thickness. The decomposition is
-incomplete and some oxygen and hydrogen remain, but the carbon is in a
-constantly increasing ratio and in proportion far above that in
-cellulose. In the cold northern climates sphagnum moss is the most
-efficient peat producing plant, but in temperate and tropical climates
-the moss is replaced by the leaves, twigs, trunks, etc., of trees,
-bushes, and vines.
-
-If these peat beds are buried beneath a layer or layers of sediment,
-especially clay, the peat is sealed up and oxidation stops almost
-entirely. With the pressure of the superincumbent beds, the peat becomes
-more and more compact, and changes to a dark-brown or black color. It is
-then known as _lignite_. If this lignite is buried still deeper, with
-consequently more pressure and more time, it changes into the still
-denser black _bituminous coal_. This is as far as it will go unless some
-new agent is added to the forces already working.
-
-The next step in the series of changes forming coal is associated with
-mountain making. In case the layers of rock containing beds of coal are
-folded, and that presupposes at least a moderate increase in heat, the
-bituminous coal is altered to _anthracite_, which is still denser, and
-so hard that it breaks with a conchoidal fracture. Alteration may be
-carried a step still farther, in case the rocks between which lie beds
-of coal are effected by such high temperatures as accompany
-metamorphism. Then all the associated hydrogen, oxygen and moisture are
-driven off, and only the carbon remains, which is then known as
-_graphite_. All steps between the stages especially designated occur.
-The following represent steps only in the series of changes.
-
-
-Peat
-
-Peat is a mass of unconsolidated vegetable matter, which has accumulated
-under water, and in which the original plant remains are still, at least
-in part, discernible. It contains a large amount of water, so that
-before it can be used as a fuel, it is cut out in blocks, which are
-piled up and left for a time to dry before using. It burns with a long
-flame and considerable smoke. This country is so well supplied with
-other fuels, that so far peat has been but little used.
-
-
-Lignite
-_brown coal_
-
-Lignite is more compact than peat, and is found buried to some depth
-under layers of clay or sandstone. It is dark brown to black in color,
-and still retains pretty clear traces of the plants from which it was
-derived. It also usually contains a considerable amount of moisture, and
-when this is dried out, it tends to crumble badly, so that it is
-undesirable to handle it much, or to ship it far, before using. It has a
-fair fuel value and is fairly widely used; but it is very desirable that
-some method be found, by which lignite could be treated to obtain its
-by-products, and at the same time make it more compact, so it would not
-crumble with the handling incident to using it in furnaces. There are
-extensive lignite deposits in this country in North and South Dakota,
-Montana, Wyoming, Colorado, New Mexico, Texas, Louisiana, and
-Mississippi.
-
-
-Bituminous Coal
-_soft coal_
-
-This type of coal is compact, black in color, and breaks readily, but
-does not crumble as badly as lignite. It contains considerable water,
-and still has some hydrogen and oxygen compounds in it. Bituminous coal
-is the product of plant remains which have been preserved for long
-periods, (millions of years), sealed from the air by the overlying beds
-of rock. The pressure has made it compact, and nearly all traces of the
-original plants have disappeared.
-
-Bituminous coal is our most abundant fuel, occurring the world over in
-seams from less than an inch in thickness to some over fifteen feet
-thick. The United States is peculiarly fortunate in the abundant and
-easily accessible deposits of this type of coal, in Pennsylvania, West
-Virginia, Ohio, Kentucky, Tennessee, Indiana, Illinois, Michigan, Iowa,
-Missouri, Kansas, Nebraska, Texas, Utah, and Colorado.
-
-The volatile constituents, hydrogen and oxygen compounds, of bituminous
-coal may be driven off by heating the coal in closed ovens, and the
-residual mass is known as _coke_, almost pure carbon. This is
-distillation, and the ovens in which this is done, without trying to
-save the volatile products, are called bee-hive ovens, while the more
-modern ovens which save the by-products are called by-products ovens. A
-ton of bituminous coal treated in the typical by-products oven, will
-yield on the average 1410 lb. of coke, 7.1 gallons of tar, 18.9 pounds
-of ammonia sulphate, etc., 2.4 gallons of light oils, 10440 cubic feet
-of illuminating gas, about half of this last being used to furnish the
-heat for the distillation. The coal-tar dye industry is built on the tar
-thus produced. Toluol, benzol, etc., come from the light oils; and half
-the gas produced is available for household illumination, etc. Coke is
-demanded, as it is a superior fuel for melting iron ores, iron and
-steel, and is made regardless of whether the by-products are used. The
-coke thus produced is hard, clean, and vesicular; but for some reason as
-yet unknown, by no means all bituminous coal will produce a coke which
-has this porous structure. These latter are known as “non-coking,” and
-are of little use to the steel industry.
-
-
-Cannel Coal
-
-This is a compact variety of non-coking bituminous coal, with a dull
-luster and a conchoidal fracture. It contains the largest proportion of
-volatile hydrocarbon compounds of any variety of coal; so that when the
-supply of petroleum and natural gas gives out, this will be one of the
-important sources of obtaining substitutes. Cannel coals occur in Ohio,
-Indiana, and eastern Kentucky. This cannel coal owes its peculiar fatty
-nature to the material from which it is derived, it being supposed to
-have resulted from the accumulation of the spores of lycopod trees, and
-their conversion to jelly-like masses by bacteria in the fresh-water
-marshes of those ancient days.
-
-
-Anthracite
-_hard coal_
-
-Anthracite coal is hard, black, has a luster, and breaks with a
-conchoidal fracture. It contains but a low percentage of volatile
-matter, and so burns with a short flame, and less smoke, than is the
-case with the other coals. It is always associated with folded rocks,
-and appears to have been formed as a result of the combined pressure and
-the higher temperatures, which accompanied mountain making. Still the
-temperature was not high enough to metamorphose the adjacent rocks. Most
-of our anthracite comes from northeastern Pennsylvania.
-
-
-Carbonite
-
-Carbonite is natural coke. It occurs in coal seams which have been cut
-by dikes or intrusions of igneous rocks, the coal having been thus coked
-by natural processes. It is not vesicular like artificial coke, for
-which reason it is not useful as a fuel. Some carbonite is found in the
-Cerillos coal field of New Mexico, in Colorado, and Virginia.
-
-
-Jet
-
-Jet is a dense variety of lignite, a fossil wood of black color, which
-takes a high polish and cuts easily into various ornamental shapes. It
-has been used for ornaments since early ancient times, beads of jet
-being found in the early bronze period in England, the supply probably
-coming from the Yorkshire coast, whence the principal supply comes even
-to the present day. In Switzerland and Belgium it was used still
-earlier, even as far back as the Palæolithic age. Jet seems then to have
-had a talismanic value, and to have been worn to protect the owner.
-About 700 A.D. crosses and rosaries began to be made of jet, the custom
-starting at Whitby Abbey, the material being obtained nearby, so that it
-came to be known as “Whitby jet,” and in the eighteenth century became
-very popular. In recent times it has been used mostly as jewelry
-suitable for mourning.
-
-
-Amber
-Pl. 61
-
-Amber is a gum which oozed from coniferous trees and was petrified. It
-is associated with lignite beds of middle Tertiary age. It is usually
-pale-yellow in color, but at times has a reddish or brownish tinge, and
-is more or less transparent. It occurs in rounded irregular lumps, up to
-ten pounds in weight, though most pieces are smaller; and is mostly
-picked up along certain coasts where it is washed ashore by the waves.
-Since the earliest records amber has been cast up on the shores of the
-Baltic, and it was used by peoples as early as in the stone age for
-ornaments and amulets. It has been found among the remains of the cave
-dwellers of Switzerland, in Assyrian and Egyptian ruins of prehistoric
-age, and in Mycenæ in the prehistoric graves of the Greeks, the first
-recorded reference to it being in Homer, and the Greek name for amber
-being _elektron_ from which our word electricity comes. All these finds
-were of Baltic amber which was doubtless gathered and traded by those
-early men. Even down to the present many men make their living, riding
-along the shore at low tide and hunting for the amber washed ashore by
-the waves. As early as 1860 the German geologists concluded that the
-source of the amber must be lignite beds outcropping beneath the sea
-level, and started mining for the amber with fair success, so that today
-two types of Baltic amber are distinguished, “sea stone” which is washed
-ashore, and “mine stone” taken from the mines. Beside the Baltic
-locality, it is found along the shores of the Adriatic, Sicily, France,
-China, and occasionally of North America.
-
-Some pieces of amber are found with insects inclosed and preserved
-almost as perfectly as if collected yesterday. They were apparently
-entangled in the gum while still viscid and completely embedded, before
-fossilization.
-
-
-                          The Petroleum Series
-
-Certain sedimentary rocks contain larger or smaller quantities of
-natural gas, petroleum, mineral tar and asphalt. These are compounds of
-carbon and hydrogen, or hydrocarbons, and range from gases to solids,
-each being a mixture of two or more hydrocarbon compounds. The crude
-petroleum may have either a paraffin base or an asphalt base: in the
-former case, when the gas, gasoline, kerosene, etc., have been removed
-by distillation, the solid residue will be paraffin, as in most of the
-Pennsylvania crude oils; while in the latter case, the solid residue
-will be an asphalt, as in most of the California and Texas crude oils.
-In the case of the paraffin series all the compounds belong to the
-paraffin group, while the asphalt is due to the presence, in addition to
-the paraffin group, of some of the benzine series of hydrocarbons.
-
-Petroleum is found in sands and shales, which were originally deposited
-on ancient sea bottoms, the shales generally being the real source of
-the petroleum. The oil was once the fatty portion of animal bodies
-(perhaps to some extent of plant bodies), and was separated during
-decomposition as a result of bacterial activity. Oil thus produced is in
-tiny droplets, which have a great affinity for clay. After being freed
-by the bacteria, the oil droplets in muddy water attach themselves to
-particles of clay, and as the clay settles the oil is carried down with
-it, the two eventually making a bituminous shale. In clear water, or in
-water which is in motion, the oil droplets rise to the surface and
-eventually distill into the air.
-
-The oil, or petroleum, may stay diffused through the shales, in which
-case we have _oil-bearing shales_, with sometimes as much as 20% of oil.
-Were there but ¹/₁₀₀₀ of a per cent of oil in a layer of shale 1500 feet
-thick, this would amount to 750,000 barrels per square mile which is
-equal to a rich production from wells. When the oil in shale amounts to
-three per cent or more, it is commercially usable. There are large
-stretches of petroleum-bearing rocks in New York, Pennsylvania, Ohio,
-Indiana, and all the way out to the Pacific coast, some of them with oil
-so abundant, that a blow of the hammer will cause them to smell of
-petroleum.
-
-In case these oil-bearing shales have been heavily overburdened and
-compressed, the petroleum may have been more or less completely pressed
-out of them. Then the droplets uniting have formed a liquid, which has
-moved out from the shale, and gone wherever it could find open spaces.
-Sandstones have frequently offered their pore space, and as it filled,
-have been thus saturated with petroleum. If the sandstones were open to
-the air, or if fissures extended from them to the surface, the oil has
-escaped to the surface and evaporated into the air. But in those cases
-where the sandstone (or other permeable rocks) was covered by an
-impervious layer, like a dense shale or clay, the oil was confined below
-the covering layer of rock. Crude oil is lighter than water; so that
-when natural gas, petroleum and water were all present in the rocks, the
-gas lies on top, the petroleum next, and the water underneath. With this
-in mind it is easy to see, that in slightly folded or undulating layers
-of rock, the gas and petroleum would be caught under upraised folds and
-domes. This is the basis of prospecting for oil.
-
-If petroleum-bearing layers are depressed far enough beneath the surface
-to be affected by the high temperatures of the earth’s interior, or have
-been near volcanic activity, of course the petroleum has been distilled
-by natural processes, and at most only the residues, like paraffin or
-asphalt, have remained. For this reason it is impossible to find
-petroleum in igneous or metamorphic rocks.
-
-
-Natural gas
-
-Natural gas is the lightest portion of crude oil, and consists mostly of
-marsh gas (“fire damp,” CH₄) together with other light hydrocarbons,
-like ethane (C₂H₆), ethylene (C₂H₄), and some carbon dioxide and
-monoxide. It is colorless, odorless, and burns with a luminous flame.
-Mixed with air it is explosive. It is found in sedimentary rocks, mostly
-sandstones, either with or without petroleum. Usually it is under
-considerable pressure, and escapes with great force wherever a hole
-permits. In time the gas all escapes through the hole or well, and then
-the well “runs out.” If petroleum is present under the natural gas, the
-hole may become an “oil well,” from which petroleum may be pumped, until
-it in turn is exhausted. The end of an oil supply is usually indicated
-by the appearance of water in the well. Natural gas is mostly associated
-with oil districts, as in Pennsylvania, Ohio, Illinois, Texas,
-California, etc.
-
-
-Petroleum Crude Oil
-Pl. 61
-
-Petroleum is a mixture of paraffin compounds all the way from the gases,
-through gasoline, kerosene, lubricating oils, and vasoline to paraffin.
-In some of the crude oils there is also an admixture of compounds from
-the benzine series, in which case, when all the volatile compounds have
-been distilled off, an asphalt remains. The different components of
-petroleum may be separated out by heating the crude oil in closed tanks,
-and drawing off the various substances at the proper temperatures.
-
-Petroleum occurs in sedimentary rocks of marine origin, usually rocks
-which also contain the shells of some of the animals, the soft parts of
-which made the oil. To have been preserved the millions of years since
-the petroleum was first formed, the oil-bearing layers must have been
-covered by some impervious layer of rock, beneath the domes and
-anticlines of which the oil has lain ever since. When such a dome or
-anticlinal fold is perforated by a well, the released oil flows to the
-surface with a greater or less rush, according to the pressure. Wells
-may keep flowing for 20 years, sometimes more, sometimes much less.
-Those which flow with the greatest pressure usually are relatively short
-lived, at times lasting only a year or two. When this easily obtained
-oil is exhausted, there is an even greater supply to be obtained by the
-distillation of the bituminous shales. Petroleum never occurs in igneous
-or metamorphic rocks, but is found in either sandstones or shales, in
-places favorable for accumulation, all across that great stretch of
-ancient sea bottoms, extending from the Appalachian Mountains to the
-Rocky Mountains, and in the Great Basin between the Rocky Mountains and
-the Sierra Nevada Range, and also to the west of the Sierras.
-
-
-Bitumen
-
-Where petroleum has escaped through pores in the rocks, or by way of
-fissures, and has come to the surface of the earth, the lighter
-components, thus exposed to the air, have vaporized and escaped, leaving
-behind a more or less solid residue, which is known as bitumen. If the
-escape was through a fissure, the bitumen may have accumulated in the
-fissure until it was filled, making vein bitumen. Or the escape may have
-been so rapid that the petroleum formed a pool or lake from the surface
-of which evaporation took place. In time such a pool will give off the
-gases and volatile compounds, only a residue remaining to make a pitch
-lake, like the one at Rancho Le Brea near Los Angeles, or an asphalt
-lake like the one on the island of Trinidad. On account of their varying
-hardness and composition, some of these bitumens have received special
-names; as:
-
-Albertite, a black bitumen with a brilliant luster on broken surfaces, a
-hardness between 1 and 2, and a specific gravity a shade over 1.
-
-Grahamite, a black bitumen, which is brittle, but has a dull luster, a
-hardness of 2, and a specific gravity of 1.15.
-
-Gilsonite or Uintaite, a black bitumen with a brilliant luster and a
-conchoidal fracture, a hardness of 2 to 2½, and a specific gravity of
-1.06.
-
-Malta is a semi-liquid viscid natural bitumen, which has a considerable
-distribution in California.
-
-The above varieties of bitumen look a good deal like coal, but are
-easily distinguished by their lightness (weight about half that of
-coal), and the fact that with only moderate heat they melt, and become a
-thick liquid like tar.
-
-
-Guano
-
-Guano is the accumulation of the excrement of birds (or of other animals
-like bats) on areas so dry that, though soluble, it is not leached and
-washed away. It may also contain some of the bones and mummified
-carcasses of the birds which died on the spot. The greatest of these
-deposits are on several small islands, just off the west coast of Peru,
-and now “farmed” by the Peruvian government. In this country there are
-no true guano beds, except a few accumulations of bat guano in certain
-caves of Kentucky and Texas, but these are not large enough to become of
-commercial importance.
-
-
-Phosphate Rock
-
-Phosphate rock is one composed chiefly of calcium phosphate along with
-various impurities, such as clay and lime. It occurs in beds, irregular
-masses, or as concretionary nodules in limestone or sand.
-
-The bedded varieties are in the older sedimentary rocks, in which the
-phosphate runs from a small percentage up to as high as 85%. Ultimately
-the phosphate came from either animal excrement, or from bacterial
-decomposition of animal carcasses and bones. In all the beds it seems to
-be true that in the first instance the phosphate was laid down as a
-disseminated deposit in marine beds, usually limestones. Later by the
-action of water leaching through the rocks, the phosphate was dissolved,
-and then redeposited elsewhere in a more concentrated form. This may be
-either in the underlying sandstones, but is more often in limestones,
-replacing the original lime.
-
-In these secondary deposits, if the phosphate has been laid down in
-cavities, the resulting phosphate will be in nodular masses. In the case
-of the Florida and Carolina deposits, these nodules have been freed from
-their matrix and washed along the river beds, remaining as pebbles in
-the river sands. The bed deposits are mostly in Kentucky and Idaho. The
-commercial use for such phosphate rocks is of course the making of
-fertilizers.
-
-
-Diatomaceous Earth
-Pl. 62
-
-Diatoms are tiny single-celled plants living in uncounted millions in
-the fresh and salt water. Each diatom builds around itself two shells
-which fit into each other like the cover and box of a pill-box, and each
-shell is marvelously ornamented. The shells are composed of silica of
-the opal type. In size the diatoms range from ¹/₅₀₀₀ of an inch in
-diameter up to the size of a pin head, and they live in such numbers
-that ordinary surface waters have hundreds of them to the quart, and
-where they are flourishing up to 250,000 in a quart. When the plants
-die, or in order to reproduce abandon the shells, these shells fall to
-the bottom of the pond or the sea, and there accumulate, often making a
-layer from a few inches thick up to hundreds of feet in extreme cases.
-If unconsolidated, this mass of tiny shells is known as diatomaceous
-earth; but if they are consolidated it is called tripolite, so named
-because the first of them used commercially came from Tripoli.
-
-As the shells are tiny and uniform in size and have a hardness of 6, the
-diatomaceous earth is used to make a great variety of polishes, scouring
-soaps, tooth paste, as a filler in certain kinds of paper, in making
-waterglass, as an absorbent for nitroglycerine, and as packing in
-insulating compounds, where asbestos would otherwise be used.
-
-Deposits of freshwater diatoms are found all over the United States,
-usually in thin layers of limited extent, especially in Massachusetts,
-New York, Michigan, etc. The marine deposits of diatoms are on a much
-larger scale, there being beds of diatoms in Anne Arundel, Calvert and
-Charles Counties, Md., up to 25 or 30 feet in thickness. In Santa
-Barbara County, Cal., there is one bed 2400 feet thick and another 4700
-feet thick, beside many other smaller ones. The enormous former wealth
-of life indicated by these great deposits may be suggested, when it is
-remembered that it takes about 120,000,000 to make an ounce in weight.
-They reproduce on an average about once in five days, so that from a
-single diatom the offspring possible under favorable conditions would
-amount to over 16,000,000 in four months or over 60 tons in a year. Of
-such an order is the potential increase of animals or plants, no matter
-how small, if the rate of reproduction is high.
-
-
-                           Metamorphic Rocks
-
-Either a sedimentary or an igneous rock, which has been altered by the
-combined activities of heat, pressure and chemical action, becomes a
-metamorphic rock. The process is essentially one, during which the
-layers of rock come under the influence of such temperatures as are
-associated with the formation of granite or lavas. Such material as is
-actually melted becomes igneous rock, but adjacent to the masses
-actually melted are other rocks which do not melt but, according to the
-temperature, are more or less changed, and these are the metamorphic
-rocks. At a distance from the molten masses the changes are minor, but
-close to the molten magmas extensive changes take place. Though not
-actually melted the rock near the heat center may be softened, usually
-is, in which case pebbles and grains or even crystals become soft and
-plastic, and, as a result of the great pressure, are flattened, giving
-the rock, when it cools again, a striated appearance. At these high
-temperatures the water in the rock and also some other substances
-vaporize, and the hot steam and vapor are active agents in making a
-great many chemical changes. In some cases material like clay is changed
-into micas, or chlorite, etc.; in other cases the elements of a mineral
-will be segregated and large crystals will appear scattered through the
-metamorphic rock, such as garnets, staurolites, etc.
-
-If one studies a layer of rock both near and far from the molten mass,
-all grades of change will appear. For example, at a distance a
-conglomerate maybe unaltered; somewhat nearer the molten mass, the heat
-and steam may have softened (but not melted) the pebbles and then the
-pressure has flattened them as though they were dough; and nearest the
-molten mass, the outlines of the pebbles are lost, only a layered effect
-remaining, and many of the materials have changed into new minerals,
-like mica, garnets, etc., but still the layered effect is preserved.
-
-One of the effects of heat and pressure is to flatten the component
-particles of the rock, so that it tends to split in a direction at right
-angles to the direction of the pressure, just as particles of flour are
-softened and flattened under the pressure of the roller; and then when
-the crust is baked it splits or cleaves at right angles to the direction
-in which the pressure was exerted by the roller. This tendency to split
-is not to be confused with either the layering, characteristic of
-sedimentary rocks, nor the cleavage characteristic of minerals. It has
-nothing to do with the way the particles were originally deposited, nor
-with their cleavage; but is due to the pressure, and resembles the pie
-crust splitting, being irregular and flaky. This is designated
-_schistosity_ if irregular and _slaty cleavage_ if regular. Schistosity
-refers to the flaky manner of splitting into thin scales as in mica
-schists. Slaty cleavage is more regular, this being due to the fact that
-the material of which slate is made is small particles of clay of
-uniform size.
-
-The metamorphic rocks are generally more or less folded, as they are
-always associated with mountain making. These major folds are of large
-size, from a hundred feet across to several miles from one side to the
-other. Such folds may also occur in sedimentary rocks or even in igneous
-rocks and simply express the great lines of yielding, or movement of the
-crust of the earth. In addition to this there is minor folding or
-contorting which is characteristic of metamorphic rocks only. When the
-rocks were heated by their nearness to the molten igneous magmas, they
-must expand, but being overburdened by thick layers of other rocks,
-there is no opportunity for yielding vertically, so the layers crumple,
-making minor folds from a fraction of an inch to a few feet across. Such
-crumpling, which is so very conspicuous especially where there are bands
-of quartzite in the rock, is entirely characteristic of metamorphic
-rocks. It is seen on hosts of the rocks about New York City, all over
-New England, and in any other metamorphic region. Plate 63 is a
-photograph of such a crumpled rock which has been smoothed by the
-glacial ice.
-
-The metamorphic rocks are the most difficult of all the rocks to
-determine and understand, because the amount of change through which
-they have gone is greatest, but for this same reason they offer the most
-interest, for the agents which caused the changes are of the most
-dramatic type of any that occur in Nature. From one place to another a
-single layer of metamorphic rock changes according to the greater or
-less heat to which it was subjected, making a series of related rocks of
-the same composition but with varied amount of alteration. For this
-reason in naming metamorphic rocks, a type is named, and from that there
-will be gradations in one or more directions, both according to
-composition, and according to amount of heat involved. If it is possible
-to follow a given layer of metamorphic rock from one place to another
-this is of great interest; for by this means, many variations in the
-type will be found, both those resulting from a different amount of
-heat, and those due to the local changes in the composition of the
-original rock.
-
-One further consideration has to be kept in mind. When a rock is
-metamorphosed the high temperatures either drive off all water, or the
-water may be used up in the making of some of the complex minerals. When
-such a metamorphic rock later comes near the surface and is exposed to
-the presence of ground water, and that leaching down from the surface
-into the rocks, several of the minerals formed at high temperatures will
-take up this water and make new minerals such as serpentine, chlorite,
-etc. They are always associated with metamorphic rocks, and have been
-metamorphic rocks, but since then have become hydrated, forming minerals
-not at all characteristic of high temperature.
-
-The following shows the relation of the sedimentary and igneous rocks to
-their metamorphic equivalents.
-
-    _Loose sediment_       _Consolidated sediment_          _Metamorphic
-                                                            equivalent_
-
-  gravel                conglomerate                    gneiss
-  sand (quartz)         sandstone                       quartzite
-  mud (sand and clay)   shale                           schist
-  clay                  shale                           slate or phyllite
-  marl                  limestone                       marble
-  peat                  bituminous coal                 anthracite to
-                                                        graphite
-                        coarse igneous rocks such as    gneiss
-                        granite, syenite, etc.
-                        fine igneous rocks such as      schist
-                        trachite, rhyolite, etc.
-
-In working out the past history of any given region, much of it is done
-on the basis of this series of equivalents. The finding of limestone,
-for instance, indicates that the given area was at one time under the
-sea to a considerable depth, that is from 100 to 1000 feet, but not
-ocean-bottom depths which run in tens of thousands of feet. Marble
-indicates the same thing, and so one can go on through all these types
-of rock.
-
-
-Gneiss
-Pl. 64
-
-Gneiss is an old word used by the Saxon miners, and is often very
-loosely used. Here it is used in its structural sense, and a gneiss may
-be defined as: a banded metamorphic rock, derived either from a
-sedimentary or an igneous rock, and is composed of feldspar, quartz, and
-mica or hornblende, and is coarse enough, so that the constituent
-minerals can be determined by the eye. It corresponds to a granite, or
-some sedimentary rock like gravel or conglomerate.
-
-Due to the action of pressure, all the gneisses are banded, and the
-original constituent particles or crystals are distorted. The lines of
-banding may be long or short, straight, curved or contorted. When the
-banding is not conspicuous, the gneiss tends toward a granite. When the
-banding is thin and the structure appears flaky, the gneiss tends toward
-a schist. The color varies according to the constituent minerals, from
-nearly white, through red, gray, brown, or green to nearly black. Plate
-64 shows one gneiss which is in a less advanced stage, the pebbles being
-simply flattened and the matrix partly altered to micaceous minerals,
-and a second gneiss which is so far advanced that the original
-constituents are all altered to other minerals and only the banded
-structure remains. This latter type would have required but little more
-heat to have completed the melting and changed this to a granite.
-
-Gneisses are very compact and have little or no pore space in them. They
-are hard and strong and resist weathering well, so that they are widely
-used as building stone: but they are not as good as granite for this
-purpose, as they split more readily in one direction and can not
-therefore be worked so uniformly as can granite.
-
-There are many varieties of gneiss, based either on their origin,
-composition, or their structure, as follows:
-
-  Granite-gneiss is one derived by metamorphism from granite.
-  Syenite-gneiss is one derived by metamorphism from syenite.
-  Diorite-gneiss is one derived by metamorphism from diorite.
-  Gabbro-gneiss is one derived by metamorphism from gabbro.
-  Biotite-gneiss is one composed of quartz, feldspar and biotite.
-  Muscovite-gneiss is one composed of quartz, feldspar and muscovite.
-  Hornblende-gneiss is one composed of quartz, feldspar and hornblende.
-  Banded-gneiss is one in which the banded structure shows clearly.
-  Foliated-gneiss is one in which there is thin irregular layering.
-  Augen-gneiss is one which has concretionary lumps scattered through
-          it.
-
-Gneisses have a wide distribution over all New England, most of Canada,
-the Piedmont Plateau, the Lake Superior region, the Rocky Mountains, the
-Sierra Nevada and the Cascade Ranges.
-
-
-Quartzite
-
-Quartzite is metamorphosed sand or sandstone, and frequently grades into
-one or the other. It is a hard compact crystalline rock, which breaks
-with a splintery or conchoidal fracture. It is distinguished from
-sandstone by the almost complete lack of pore spaces, its greater
-hardness and by its crystalline structure. In practice it may be
-distinguished by the fact that a sandstone in breaking separates between
-the grains of sand, while a quartzite breaks through the grains.
-
-Some quartzites are almost pure quartz, but others contain impurities of
-clay, lime or iron, which were in the original sandstone. These alter in
-the metamorphism to such accessory minerals as feldspar, mica, cyanite,
-magnetite, hematite, calcite, graphite, etc. The color of quartzite when
-pure is white, but may be altered to red, yellow, or green by the
-presence of these accessory minerals.
-
-On account of the difficulty of working the quartzites, they are not
-much used in building, though they are very durable. When crushed they
-often make excellent road ballast, or filling for concrete work. The
-pure varieties are sometimes ground and used in the manufacture of
-glass.
-
-According to the accessory mineral, the following varieties may be
-distinguished; chloritic-quartzite, micaceous-quartzite,
-feldspathic-quartzite, etc.
-
-Quartzites are common in the New England, the Piedmont Plateau, and Lake
-Superior metamorphic regions, and also in many western localities.
-
-
-Schist
-Pl. 65
-
-Schist is a loosely used term, but is used here in its structural sense.
-It includes those metamorphic rocks which are foliated or composed of
-thin scaly layers, all more or less alike. The principle minerals are
-recognizable with the naked eye. In general schists lack feldspar, but
-there are some special cases in which it may be present. Quartz is an
-abundant component of schists; and with it there will be one or more
-minerals of the following groups: mica, chlorite, talc, amphibole or
-pyroxene. Frequently there are also accessory minerals present, like
-garnet, staurolite, tourmaline, pyrite, magnetite, etc.
-
-All schists have the schistose structure, and split in one direction
-with a more or less smooth, though often irregular, surface. At right
-angles to this surface they break with greater or less difficulty and
-with a frayed edge. As they get coarser, the schists may grade into
-gneisses, losing their scaly structure: while on the other side, as the
-constituent minerals become finer and so small as to be difficult of
-recognition, schists may grade into slates.
-
-The varieties of schist are based on the mineral associated with the
-quartz; as mica-schist, chlorite-schist, hornblende-schist, talc-schist,
-etc.
-
-The color also is due to the constituent minerals other than quartz and
-ranges widely, mica-schists being white to brown or nearly black,
-chlorite-schists some shade of green, hornblende-schists from dark green
-to black, talc-schists white, pale-green, yellowish or gray, etc.
-
-Schists are found all over the same regions as gneisses and quartzites,
-_i.e._, New England (especially good exposures of schist being seen
-about New York City), the Lake Superior region, Rocky Mountains, etc.
-Beside these regions where it occurs native, there are boulders of
-schist all over the glaciated areas of eastern and northern United
-States.
-
-
-Slate
-
-Slate is a metamorphic rock which will split into thin or thick sheets,
-and is composed of grains so fine as to be indistinguishable to the
-unaided eye. The cleavage is the result of pressure during metamorphism,
-and has nothing to do with the bedding or stratification of the
-sedimentary rock from which it was derived. The original bedding planes
-may appear as streaks, often more or less plicated, and running at any
-angle with the cleavage. If these bedding streaks are abundant or very
-marked, they may make a slate unsuitable for commercial uses. The slaty
-cleavage may be very perfect and smooth so that the rock splits into
-fine sheets, in which case it is often used for roofing slate; but by
-far the greater part of the slates have a cleavage which is not smooth
-or perfect enough so that they can be so used. Slates are the
-metamorphic equivalents of shales and muds, and represent the effect of
-great pressure but with less heat than is associated with schists or
-phyllite, and consequently with less alteration of the original mineral
-grains.
-
-The color ranges from gray through red, green and purple to black. The
-grays and black are due to the presence of more or less carbonaceous
-material in the original rock, the carbon compounds having changed to
-graphite. The reds and purple are due to the presence of iron oxides,
-and the green to the presence of chlorite.
-
-While the particles of slate are so small as to be indistinguishable to
-the unaided eye, the use of thin sections under the microscope shows
-that slate is composed mostly of quartz and mica, with a wide range of
-accessory minerals, like chlorite, feldspar, magnetite, hematite,
-pyrite, calcite, graphite, etc.
-
-According to their chief constituents slates may be distinguished as
-argillaceous-slate or _argillite_, bituminous-slate, calcareous-slate,
-siliceous-slate, etc.
-
-Slate will be found here and there in the metamorphic areas of New
-England, the Piedmont Plateau, the Lake Superior region, and in many
-places in the west.
-
-
-Phyllite
-Pl. 66
-
-Phyllite is a thinly cleavable, finely micaceous rock of uniform
-composition, which is intermediate between slate and mica schist. In
-this case the flakes of mica are large enough to be distinguishable to
-the eye, but most of the rest of the material can only be identified
-with the aid of a microscope. It is mostly quartz and sericite. Phyllite
-represents a degree of metamorphism greater than for slate, but less
-than for schist; and it may grade into either of these other rocks.
-Garnets, pyrite, etc., may be present as accessory minerals. The color
-ranges from nearly white to black, and it is likely to occur in the same
-places as do slates.
-
-
-Marble
-Pl. 66
-
-This is a broad term, and includes all those rocks composed essentially
-of calcium carbonate (limestones) or its mixture with magnesium
-carbonate (dolomite), which are crystalline, or of granular structure,
-as a result of metamorphism. It takes less heat to metamorphose a
-limestone, and for this reason the marbles have a more crystalline
-structure than most metamorphic rocks; and they do not have the tendency
-to split or cleave which is so characteristic of most metamorphic rocks.
-It is only when there is a large amount of mica present that the typical
-schistosity appears. Commercially the term marble is used to include
-true marble and also those limestones which will take a high polish; but
-in this book, and geologically speaking, no rock is a marble unless it
-has crystalline structure.
-
-Marbles range widely in color according to their impurities. Pure marble
-is white. Carbonaceous material in the antecedent limestone is changed
-to graphite in the metamorphic process, and makes the marble black, but
-appears usually in streaks or spots, rather than in any uniform color.
-An all black “marble” is usually a limestone. The presence of iron
-colors the marble red or pink. Chlorite makes it green, etc.
-
-Various accessory minerals are common in marbles, such as mica,
-pyroxene, amphibole, grossularite among the garnets, magnetite, spinel,
-pyrite, etc., through a long list.
-
-Because it cuts readily in all directions and takes a high polish,
-marble is widely used as a building stone. In the moist climate of the
-United States it suffers in being soluble in rain water when used on the
-outside of a building: but for interior decoration it furnishes some of
-the finest effects.
-
-The largest marble quarries are developed in Vermont, Massachusetts, New
-York, Pennsylvania, Georgia, Alabama, Colorado, California, and
-Washington.
-
-
-Steatite
-_Soapstone_
-
-Steatite is a rock composed essentially of talc, which is associated
-with more or less impurities, such as mica, tremolite, enstatite,
-quartz, magnetite, etc. It is found in and with metamorphic rocks, and
-is a rock which has been modified by hydration from a metamorphic
-predecessor. It was probably first a tremolite or enstatite schist, in
-which, after the metamorphic rock came into the zone where ground water
-exists, the tremolite or enstatite was altered to talc, the impurities
-remaining much as they were in the first place.
-
-It is bluish-gray to green in color, often soft enough to cut with a
-knife, and has a greasy feel. It is very resistant to heat and acids;
-for which reasons it has proved very useful commercially in making
-hearthstones, laundry tubs, and fire backs; and, when powdered, in
-making certain lubricants. The Indians, in the days before Columbus,
-took advantage of the ease with which it is cut, to make from it large
-pots for holding liquids, which are today among the greatest treasures
-in collections of Indian relics. They also carved pipe-bowls and various
-ornaments and amulets from soapstone.
-
-It is found in Vermont, Massachusetts, New York, New Jersey,
-Pennsylvania, Maryland, Virginia, North Carolina, Georgia and
-California.
-
-
-Serpentine
-Pl. 67
-
-Pure serpentine is the hydrated silicate of magnesium, as described
-among the minerals on page 138. Serpentine rock is serpentine with more
-or less impurities, such as pyroxene, amphibole, olivine, magnetite,
-chromite, calcite, magnesite, etc. It often also contains mica and such
-garnets as pyrope, as accessory minerals. Serpentine, like steatite,
-always occurs in and with metamorphic rocks, and was originally a
-metamorphic rock, but has since been changed by the hydration of its
-silicates, when it came into the zone in which ground water is present.
-In the first instance it was some sort of shale, clay and dolomite,
-which was metamorphosed to an amphibole or pyroxene schist. When this
-was exposed to the action of ground water, the amphibole or pyroxene
-minerals were changed to serpentine, resulting in a rock composed mostly
-of serpentine, but retaining the impurities which were in the
-metamorphic rock, and perhaps adding to them such amphiboles and
-pyroxenes as were not altered during the hydration process. The above is
-the commonest type of serpentine rock. It can and sometimes has been
-formed in a similar way from an igneous predecessor, by the hydration of
-its silicate minerals. In this latter case the serpentine would not be a
-modified metamorphic rock, but a modified igneous one. It is a case
-where such a rock as a diorite or a gabbro is exposed to ground water
-and the pyroxene present altered to serpentine. A serpentine formed in
-this way would be a very impure one.
-
-Serpentine rock is used as an ornamental stone for interior decoration,
-because it takes a high polish and has pleasing colors, various shades
-of green. It is however decidedly soft and will stand very little
-exposure to weather, and it is also filled with seams which make it
-difficult to get out large slabs.
-
-Serpentine rock occurs fairly commonly in the metamorphic belt of New
-England and the Piedmont Plateau, and in some of the western states,
-especially California, Oregon, and Washington.
-
-
-Ophiolite
-_Ophicalcite_
-
-This name is given to marbles which are streaked and spotted with
-serpentine. They are a mixture of green serpentine and a white or nearly
-white calcite, magnesite or dolomite in variable proportions.
-
-Ophicalcite occurs in and with metamorphic rocks, and represents an
-impure limestone which has been metamorphised, the lime becoming marble,
-and the impurities becoming such silicates as pyroxene, amphibole, or
-olivine. This metamorphic rock has then come into the zone of
-ground-water and the silicate minerals have been changed by hydration to
-serpentine. Ophicalcite is then a metamorphic rock, in which secondary
-chemical changes have since taken place. It may have a wide range of
-accessory minerals present, such as magnetite, chromite, pyrope among
-the garnets, olivine, etc. Verde antique is a trade name for one of the
-ophiolites.
-
-While not abundant, ophicalcite is in good demand as an ornamental stone
-for interior work; for it takes a high polish, and is beautiful; but, on
-the other hand, it will not stand exposure to the weather for the
-calcite is soluble, and there are numerous seams and cracks in it making
-it difficult to obtain large slabs.
-
-It occurs in Quebec, Canada, in the Green Mountains of Vermont, and in
-the Adirondack Mountains.
-
-
-
-
-                               CHAPTER V
-                          MISCELLANEOUS ROCKS
-
-
-There are a few rocks which do not fit into any of the three groups
-described, such as concretions, geodes, meteorites, etc., and they are
-gathered together here. There is also one type of rock, which really
-belongs among the minerals, but is likely not to be so recognized at
-first glance, and that is the material filling veins. These last are
-sometimes designated “vein rocks,” but are really massive deposits of
-one, two or more minerals, and should be referred to the minerals when
-found.
-
-
-                              Concretions
-
-In the sedimentary rocks there frequently occur inclusions of a nature
-different from the surrounding rock. In shape they are usually rounded,
-nodular, spherical, discoidal, ovate, flattened, elongated or
-ring-shaped, or combinations of the foregoing, making often curious and
-fantastic forms. In size they range from a fraction of an inch in
-diameter to several feet through. When broken, they may show a nucleus,
-around which more or less concentric layers have formed, or neither
-nucleus nor concentric structure may be visible. The layered structure
-of the surrounding rock in some cases continues right through the
-nodular mass. These structures are called concretions, and their
-formation in all cases is at least due to similar reactions.
-
-In general the concretions differ from the surrounding rock in
-composition, but are usually composed of some one of its impurities, of
-lime in the clays or silica in limestones, of iron oxide in sandstone,
-etc. They seem to have originated as a result of the solution of the
-minor mineral, and then its redeposition around some center or nucleus.
-In many cases the nucleus is organic, such as a leaf, a shell, a bone,
-etc., so that when the concretion is split, in its center will be found
-the perfect imprint of the leaf, or the shell of a mollusk, or a bone of
-a higher animal, sometimes a whole skeleton. Again the nucleus may be
-inorganic like a grain of sand; and in still other cases no nucleus can
-be found, though there was probably one in the beginning. What has
-happened is somewhat like the case of accessory minerals in igneous and
-metamorphic rocks. A layer of sediment was laid down, including in it,
-here and there, something foreign to the run of the rock. Later when the
-water leaches through this rock, impregnated with lime for instance, it
-comes to the point where a leaf is decomposing. The products of the leaf
-decomposition are different from what is already present in solution,
-and may precipitate some of the lime in that neighborhood. As long as
-leaf decomposition continues the precipitation in that region will
-continue and increase the size of the concretion. This sort of action
-accounts for many of the concretions, especially those about organic
-remains. In some other cases where there is no nucleus, as the flint in
-chalk, what has taken place is that the small amounts of silica in the
-lime have been dissolved, and then around some center has constantly
-been added more and more non-crystalline silica until a mass of flint
-has accumulated. There may be a considerable variety of ways to account
-for different concretions, but in all cases solutions of one mineral
-have come in contact with solutions of a different kind, and
-precipitation about a center has resulted.
-
-
-Clay stones
-Pl. 68
-
-Of all the concretions these are perhaps the commonest, being found in
-the clays of all types and in many regions. They are made of lime and
-precipitated around some nucleus of foreign matter. The shapes vary
-widely, usually discs, flattened ovals or even rings, in most all cases
-however flattened. This is indicative of the water moving though the
-clay more freely in some layers than others. Often clay stones occur so
-abundantly that two or more have grown together making fantastic shapes,
-sometimes resembling animals, and all sorts of fancied but unrelated
-objects. As the clay stones have grown the clay has not been pushed
-aside, but has been incorporated within the concretion; so that when a
-concretion is dissolved in acid, it yields not only the lime, which is
-its reason for being, but also a large amount of clay.
-
-Claystones are found in clays most anywhere, usually occurring in
-certain layers and being absent from others.
-
-
-Lime concretions
-
-These are found mostly in shales which carry a high percentage of clay
-as impurities, and are characteristic of the older geological
-formations, especially ancient sea bottoms. They are likely to have as a
-nucleus some shell, fish bone, or a leaf, which when the concretion is
-split, reveals a wonderfully preserved portion of an animal or a plant,
-which was buried millions of years ago. The lime concretion is closely
-related to the claystone, and is really a claystone which has been
-buried so long that the surrounding matrix has changed to a shale
-instead of remaining clay.
-
-One of the most famous localities for these lime concretions is Mazon
-Creek, Illinois, where thousands of these concretions have been picked
-up and split to study the organic remains included. The commonest
-objects found are fern leaves, like the one on Plate 68. But about once
-in a thousand times they inclose a spider or insect, and once in ten
-thousand times the skeleton of an amphibian, which is of especial
-interest, as here have been thus found the remains of the very earliest
-of the land animals. These remains were inclosed in these concretions
-during the coal age, probably 50,000,000 years ago, and once inclosed
-all the hard parts have been as well preserved after that long interval,
-as they were immediately after being inclosed in the concretion. Lime
-concretions range from less than an inch in diameter to several feet
-through. They are not confined to shales, but sometimes occur in
-sandstones, in this case also usually having as a nucleus either a
-shell, or the bone, or bones, of some animal.
-
-They are likely to be found anywhere in the limestone belt, from the
-Appalachian Mountains to the Rocky Mountains, or in the Great Basin, or
-on the Pacific Coast. Often they have been mistaken for turtles and
-other objects. A good many of the cases where the head or body of
-animals “petrified with all the flesh” are reported, it is one of these
-concretions which has a shape sufficiently like the part described, for
-the imagination to construct the rest.
-
-
-Septeria
-Pl. 69
-
-Septeria are lime concretions, which, after they had formed, have shrunk
-and developed a series of cracks running through them in all sorts of
-directions, and since then the cracks have been filled with various
-minerals, such as calcite, dolomite, and siderite. These make a series
-of veins which intersect the concretion, in a sort of network. Septeria
-are mostly of considerable size, ranging from six inches in diameter to
-several feet through. They are characteristic of the shales of ancient
-sea bottoms, especially those of Devonian age in New York, and
-Pennsylvania, and those of Cretaceous age in Wyoming, Montana and the
-Dakotas.
-
-
-Flint concretions
-
-The silica in limestones is often segregated into nodular masses of
-varying sizes, to make concretions of flint. Such masses have grown in
-the limestone, and, while growing, have either pushed away, or dissolved
-the adjacent limestone, so that the flint nodule is pure silica. They
-are especially characteristic of the chalk beds, and of ancient
-limestones which formed on the floor of the sea, like the Helderberg
-Limestone of New York, Pennsylvania, Ohio, etc. When thin sections are
-cut through these flints, and examined under the microscope, many
-remnants of the shells of plants and animals are still recognizable. A
-nucleus is seldom found, but in some cases there is a fossil in the
-nodule about which the concretion doubtless formed. The spicules of
-sponges, shells of diatoms, and of radiolarians seem to have contributed
-most of the material from which flint concretions are formed. In
-addition to the silica there are frequently inclosed in these nodules
-the horny jaws of various sea worms, and a host of spiny balls the
-relationships of which are still unknown.
-
-
-Sandstone concretions
-
-There are two types of sandstone concretions, first those which are
-cemented with lime, and second those cemented with iron oxide. The
-concretions bound by lime are especially characteristic of sandstones
-which were laid down as river deposits, either in the channels or on the
-flood plains, and also the sandy deposits resulting from wind
-deposition. In these cases the concretions will mostly be found to have
-formed around some organic nucleus, most frequently about a bone, or
-group of bones, of some ancient animal. In this country they are mostly
-found in the arid and semiarid sections of the West, where the present
-day wind erosion exposes the harder parts of bluffs, etc.
-
-The second type of sandstone concretion is the one in which the cement
-is most often limonite, less often hematite. These concretions are less
-dense than the lime ones, and in some cases the limonite is only
-precipitated at a distance from the nucleus, which has resulted in the
-formation of a hollow shell, filled with loose sand. This is especially
-characteristic of certain concretions, found in a gravel or coarse sand
-in the region of Middletown, Del.
-
-
-Oolites
-
-In large bodies of water like the sea and some larger lakes we find
-concretions which have formed, or are still forming, about tiny grains
-of sand, which are still being moved about by the waves and currents. In
-such cases not only are great masses of concretions formed but they have
-very clearly marked the concentric layering, which shows that they have
-increased in size, sometimes more rapidly and sometimes more slowly.
-Where great masses of such concretions have formed the resulting rock
-appears like a great mass of small eggs, whence the term oolite. The
-cement may be any one of several substances, but lime, silica, and
-hematite are perhaps the most common. Here and there are found larger or
-smaller masses of this oolite. In some cases it would appear that the
-material was precipitated by the action of bacteria. Such for instance
-is probably the origin of the Clinton iron ore, a bed of oolitic
-hematite, extending from New York State all down the Appalachian
-Mountains to Alabama.
-
-
-Pisolite
-Pl. 69
-
-When the concretions, formed in exactly the same manner as in the case
-of oolite, are of a size bigger than a pea, then the rock is known as
-pisolite.
-
-
-                           Other Concretions
-
-Though less abundant concretion may form from still other substances.
-Hematite has been mentioned, and when concretions are made of this
-material, either they have been deposited by bacteria, or were formed as
-limonite and the water of crystallization of this latter mineral driven
-off.
-
-Manganese concretions are found on the floor of the ocean at maximum
-depths, and brought to the surface by dredging.
-
-
-                                 Geodes
-
-Geodes are nodules, which, when broken open, are found to be hollow and
-the cavity lined with one or more minerals. They represent a special
-case of minerals in a cave. There was in the first place a cavity in the
-surrounding rock, usually of sand or clay. As the water leached through
-the surrounding rock, it became saturated with one or more minerals and
-then coming into the cavity, deposited the minerals, either as crystals,
-or as a non-crystalline mass, lining the cavity. Thus the inside is
-often a beautiful cluster of bristling crystals, or it may be simply
-layer on layer of chalcedony of any color. Before this process had gone
-so far as to completely fill the cavity, erosion had dislodged the mass,
-and it has been found. One usually recognizes that it is a geode by the
-fact that it is far too light to be a solid rock, and then it may be
-carefully broken. They are characteristic of certain formations; so that
-having accidentally broken the first one, others can be carefully opened
-to display the beauty of the interior. The geode illustrated on Plate 70
-is lined with quartz crystals, but near by were found many others, some
-of which had chalcedony and some jasper as a lining. Such crystallined
-nodules are usually called geodes so long as they occur in a softer
-matrix so that they are easily dislodged, and until they reach a size of
-three or four feet in diameter.
-
-
-                                Pebbles
-
-When picked up either from brook beds, sea beaches, or the open plain,
-there are few forms of rock which tell a story of the past more
-completely than do pebbles; and any one, who enjoys reading a story
-written in form, structure and composition, will find in pebbles one of
-the most satisfying and at the same time testing exercises. The story
-may be complex or simple according to what has happened to the parent
-rock, and to that is added what happened since the pebble left the ledge
-where it was a part of a great mass. One must not forget to take into
-consideration where the pebble was found and the character of its
-associates. This sort of exercise is recommended to all interested in
-rocks. It will yield something upon first trying, and more on prolonged
-study; and the fullness with which it is done will test one’s knowledge
-of the meaning of rocks as nothing else will do. As a sample of this
-sort of exercise let us take the two pebbles illustrated on Plate 71.
-
-The upper one is a common quartz pebble picked up in a New England brook
-bed. Such pebbles are common all over the country formerly covered by
-the glacial ice sheet. It is crystalline quartz, but the individual
-crystals are not distinguishable, and such quartz is typical as the
-filling of veins. It therefore goes back to a time when the rocks were
-fissured, probably in connection with the folding accompanying mountain
-making far to the north in Canada. Into the fissures thus formed seeped
-the water which had been leaching through the adjacent rocks, and it was
-saturated with silica which it had dissolved from those rocks. In the
-open fissure the quartz was deposited as crystals, which grew finally
-filling the fissure and crowding each other so that all the faces were
-obliterated. The quartz vein was complete, but it must have been far
-below the surface of the ground. Time must have passed, thousands of
-years of it, until, in the weathering away of the mountain system, the
-many feet of overlying rock were removed and this vein was brought to
-the surface. As the quartz is harder than the adjacent rocks, the vein
-soon projected as a ledge. The effect of changes of temperature in
-alternately expanding and contracting the rocks developed cracks, into
-which water worked its way, and then the breaking was hastened by the
-expansion which takes place when water freezes, and in exposed regions
-is so effective, because the freezing and thawing are so often repeated.
-Finally an angular fragment of quartz was dislodged and lay on the
-surface, resistant to the solvent power of the rain. In this case this
-happened just before the advance of the great ice sheet. When that came
-to the place where the fragment lay, it was picked up along with all
-other loose material and partly shoved in front of, but probably mostly
-carried frozen in the ice, and journeyed one, two, three hundred,
-perhaps a thousand miles. This took many years for the ice moved only a
-few feet a day. Finally however it came to the point where the ice
-melted as fast as it advanced, and our quartz fragment was dropped at
-the front of the ice sheet along with other great masses of till. Here
-there was abundant water, partly from the melting of the ice, and partly
-from the storms which must develop where there are such contrasts in
-temperature, as there would be over the ice, on one hand, and over the
-bare land in front of the ice on the other hand. A torrent picked up our
-fragment and started it on a second journey, banging against other
-stones as it rolled along down the stream bed, every time it struck
-another stone bruising the corners which soon became rounded. Thus from
-time to time during high water the quartz fragment, becoming rounder
-every time it moved, journeyed down stream, until it came to the point
-where the stream emptied into a lake. Here the current was checked and
-the stone dropped to the bottom along with other larger stones to make
-the delta at the mouth of the stream. There it lay as long as the lake
-existed, and would be lying now, but that in New England a tilting
-movement of the land tipped the north end of the lake up and the water
-all ran out. Then the stream began to flow over its own delta and in
-time of freshet tore a channel down through the old delta carrying the
-pebble still further down, until it came to the level stretch which
-represented the old lake’s bottom and there it dropped the pebble in its
-bed. And there it was found and picked up to become the pebble which
-told the above story of its life, and to repeat it as often as anyone
-will look at it with a seeing eye.
-
-
-The second pebble is quite a different one. It was picked up in a gravel
-bank along a railroad cut, just at the foot of Mt. Toby in
-Massachussetts, and the writer has used it many times to test his
-students, to see if they could read the story which it tells.
-
-It consists of two sorts of rock, the one, angular fragments of a
-hornblende schist, the other, a fine-grained granite filling all the
-spaces between the fragments of schist, even in cracks less than a
-quarter of an inch wide. The schist is the older rock and in its first
-appearance represents a deposit of mud (clay and sand) on the floor of
-the ocean, well out from the shore, and somewhere off to the east of Mt.
-Toby, perhaps ten miles, perhaps more, from the place where it was
-found. This was back in early Palæozoic times, millions of years ago.
-
-This deposit was buried by further layers of sediment on the sea bottom
-and cemented into a shale. Then during a mountain making period the
-region was folded, and the sediments were altered by the combined
-pressure and heat, our layer of rock becoming a hornblende schist. After
-that happened considerable time must have passed, but just how much is
-not indicated by the pebble, before another period of disturbance took
-place, during which this deep seated schist was faulted, and shattered
-to fragments along the line of breaking. This accounts for the angular
-fragments. Then into the fissure thus formed was pressed a molten magma,
-which while liquid enough to flow and be squeezed into every opening
-could not have been very hot; for not even the corners of the schist
-fragments are melted or altered, so as to appear any different from the
-mass of the schist. The molten magma cooled rather slowly, making a
-fine-grained granite. This must all have taken place far below the
-surface, or the magma would have cooled into a felsite or dense lava.
-
-Again a long time must have elapsed, while the rock overlying our piece
-was eroded away, so it could come to the surface. Just about the time it
-did come to the surface, the Connecticut Valley was formed by a great
-block, 95 miles long by fifteen to twenty miles wide, dropping down six
-or eight thousand feet (probably not all at once but by one or two
-hundred feet at a time) between two north and south faults. This took
-place in the Triassic Period. Of course the streams then began to wash
-sand and stones of all sizes into the hole. Our pebble was one of these.
-While still an angular fragment, lying perhaps ten miles east of the
-Connecticut Valley, a stream started it moving, and as it rolled along
-the brook bed, it was battered and rounded to its present shape, and
-finally tumbled over a waterfall to the bottom of the great hole, which
-had been formed as described above. Here with other stones it formed
-part of a coarse gravel, coarsest near the sides of the hole, and finer
-toward the middle; for the material was further distributed in the
-bottom of the valley. Our stone stayed pretty near the side and was soon
-buried beneath hundreds of feet of similar material. The leaching water
-dissolved enough iron rust so that this acted on the lower layers as a
-cement and bound the whole mass into a conglomerate.
-
-Here for some millions of years our pebble rested, while above it was
-piled sand and gravel and a couple of sheets of lava, until the hole was
-filled, and our pebble was near the bottom of the mass. Later movements
-of the land raised the whole region, fully six thousand feet, and
-erosion went on for other millions of years. The conglomerate and
-sandstone wore away faster than the metamorphosed rocks on either side
-of the filled valley, so that a new valley, the present Connecticut
-Valley, came into existence.
-
-When our pebble finally came near to the surface on the side of Mt. Toby
-(a mound of conglomerate which somehow was protected and wore down a
-little less rapidly than the conglomerate on either side of it), it was
-just about the time of the glacial period. The great ice sheet went over
-the mountain removing all the loose material and some more of the solid
-conglomerate. This brought our pebble to the surface, but too late to be
-moved by the ice. However as soon as the ice left the Mt. Toby region,
-the rains fell, and in the further weathering of the conglomerate, the
-cement holding our pebble in place was dissolved and it was freed. At
-once a tiny brook started it rolling down the side of the mountain, a
-brook so small that when the pebble reached the foot of the slope it did
-not have power to carry it further. Here there gathered a fan-shaped
-mound of such pebbles, known as an alluvial fan. It rested here not over
-a couple of thousand years, when the Central Vermont R. R. cut a groove
-through the fan, using the material for ballast, and here the pebble was
-found and brought home.
-
-
-                               Meteorites
-
-Meteorites can hardly be called common, but there is always a chance of
-finding one, and their interest is so great, that none should escape
-because unrecognized.
-
-Meteorites are visitors to the earth from space, and they bring to us
-knowledge of the composition of planets and solar systems, other than
-our own. It is of interest to note, that while they have brought to us
-some combinations of elements which do not occur in the earth, still
-they have not brought any element with which we were not already
-familiar. They are popularly known as “falling” or “shooting stars,”
-though of course they are not stars, but only small masses of matter
-which are entirely invisible until they come inside our atmosphere.
-
-In space there are many small (compared with the size of the earth)
-chunks of matter, each pursuing its solitary way around the sun, or
-wandering through space along paths entirely unrelated to the sun. From
-time to time one of these passes near enough to the earth, so as to be
-influenced by its attraction, and then comes rushing toward it at
-tremendous speed, 20 to 30 miles per second. As soon as it comes into
-the atmosphere, even the very attenuated atmosphere, a couple of hundred
-miles above the surface, friction heats the surface of the meteor until
-it glows, and by that light we see the so-called shooting star, often
-with a trail of luminous matter streaming out behind. Of course in using
-this term “shooting star,” we understand the meteor is no star, for they
-are bodies as big as our sun, shining at distances billions of miles
-away.
-
-As the meteor rushes through the atmosphere it may all burn up, no large
-fragment reaching the earth’s surface. The luminous matter streaming out
-behind is material which has melted and dripped off the main mass. As
-this oxidizes and cools, that part which did not become gaseous will
-finally fall to the earth as fine dust. When however a meteor actually
-falls to the earth, its surface is still hot, though probably there has
-not been time enough for much heat to be transmitted to the interior. At
-any rate they do not show any alteration due to this cause. On landing
-and sometimes before they land meteors break into two or more pieces.
-When found the surface always shows the effects of the heat generated by
-the friction of passing through the air, the surface being smoothed, and
-covered with stream lines and melted out pits and hollows, and the outer
-surface consisting of a thin crust, making an appearance, which once
-seen, can hardly be mistaken.
-
-There are two types of meteorites, those made wholly or largely of iron
-with some nickel, and appearing like great chunks of iron, and those
-which are stony and resemble a granite boulder. In collections the first
-sort, _i.e._ iron meteorites, are most abundantly represented, because
-most easily recognized when found. They consist of masses of iron and
-nickel with small amounts of other elements, ranging in size from the
-Cape York meteorite, which fell in northern Greenland in 1894 and was
-later brought by Peary to the American Museum, and weighs some 36 tons,
-down to small grains as small as a grain of wheat. The largest one which
-has fallen in the United States was the Willamette meteorite weighing
-some 15 tons, and falling 19 miles south of Portland, Oregon. These and
-all iron meteorites have the iron in crystalline form which is readily
-seen if the meteorite is cut, and the surface thus made polished, then
-etched with acid, which is put on and quickly washed off. Every
-meteorite has its particular pattern, as illustrated on Plate 72, and by
-these patterns can be identified. Meteorites have a high value and are
-eagerly sought by certain large institutions and collectors. Since the
-crystalline structure is so characteristic of each fall, when a new
-meteorite is found, it is usually cut in two, and one part retained by
-the finder or some institution; while the other part is cut into small
-pieces, an inch or two on a side and a quarter of an inch thick, but
-each large enough to show the characteristic pattern. These are
-distributed largely by sale to other collectors. Thus a great meteorite
-collection consists of a few large meteorites and a great many small
-portions of other meteorites.
-
-The second type of meteorite is the stony meteorite. Where meteorites
-have been located as they fell and recovered, the majority of them were
-of this type, so that probably more than half of the meteorites which
-fall are of the stony type. However when the stony meteorite is exposed
-to weathering it takes only a very short time before the surface is
-eroded off and then such a meteorite looks like any other boulder and
-probably most of them fail to be recognized, and so have been lost.
-Because they have so much greater variety, they are in many ways of
-greater interest than the iron type.
-
-It is desirable that every one have his eye out for meteorites, and when
-found it is desirable that the fact should be reported to some one of
-the great institutions which collect them, such as the National Museum
-in Washington, or the American Museum in New York. Each one should be on
-record even if it is desired to keep it in a private collection.
-
-
-                                Fossils
-
-In the sedimentary rocks one is apt to find remains of some of the
-animals and plants that lived at the time the rock was forming. While
-the soft parts of animals decompose rapidly, shells and bones are likely
-to be buried in the sediments, and if the conditions have been
-favorable, these remains may be preserved more or less perfectly. All
-through the millions of years that sedimentary rocks have been forming
-in the sea, in lakes, on river flood plains and in wind swept deserts,
-there was an abundance of life, as much as there is today; and our
-knowledge of that life is derived from these buried fossil remains, so
-that fossils have a great historic interest.
-
-However as there have lived and died several times as many different
-kinds of animals as live today, the study of fossils becomes a separate
-subject, which cannot be treated in this book. Should any collector of
-rocks and minerals come upon fossils, he is opening a new field, and it
-will be necessary to turn to other sources for their identification.
-General books on this subject are scarce, but one or two are given in
-the literature list.
-
-
-   A List of the Elements, the Abbreviations Used for Them, and Their
- Atomic Weight, Which Is Approximately the Number of Times Heavier They
-                           Are Than Hydrogen.
-
-                          Name               Oxygen = 16
-
-              Aluminium, Al                           27
-              Antimony, Sb                           122
-              Argon, Ar                               40
-              Arsenic, As                             75
-              Barium, Ba                             137
-              Beryllium, Be                            9
-              Bismuth, Bi                            209
-              Boron, B                                11
-              Bromine, Br                             80
-              Cadmium, Cd                            112
-              Cæsium, Cs                             132
-              Calcium, Ca                             40
-              Carbon, C                               12
-              Cerium, Ce                             140
-              Chlorine, Cl                            35
-              Chromium, Cr                            52
-              Cobalt, Co                              59
-              Columbium, Cb                           93
-              Copper, Cu                              64
-              Dysprosium, Dy                         162
-              Erbium, Er                             167
-              Europium, Eu                           152
-              Fluorine, F                             19
-              Gadolinium, Gd                         157
-              Gallium, Ga                             70
-              Germanium, Ge                           63
-              Glucinum, Gl                             9
-              Gold, Au                               197
-              Hafnium, Hf                            179
-              Helium, He                               4
-              Holmium, Ho                            165
-              Hydrogen, H                              1
-              Indium, In                             115
-              Iodine, I                              127
-              Iridium, Ir                            193
-              Iron, Fe                                56
-              Krypton, Kr                             84
-              Lanthanum, La                          139
-              Lead, Pb                               207
-              Lithium, Li                              7
-              Lutecium, Lu                           175
-              Magnesium, Mg                           24
-              Manganese, Mn                           55
-              Mercury, Hg                            201
-              Molybdenum, Mo                          96
-              Neodymium, Nd                          144
-              Neon, Ne                                20
-              Nickel, Ni                              59
-              Nitrogen, N                             14
-              Osmium, Os                             190
-              Oxygen, O                               16
-              Palladium, Pd                          107
-              Phosphorus, P                           31
-              Platinum, Pt                           195
-              Potassium, K                            39
-              Præseodymium, Pr                       141
-              Protoactinium, Pa                      231
-              Radium, Ra                             226
-              Radon, Rn                              222
-              Rhenium, Re                            186
-              Rhodium, Rh                            103
-              Rubidium, Rb                            85
-              Ruthenium, Ru                          102
-              Samarium, Sm                           150
-              Scandium, Sc                            45
-              Selenium, Se                            79
-              Silicon, Si                             28
-              Silver, Ag                             108
-              Sodium, Na                              23
-              Strontium, Sr                           88
-              Sulphur, S                              32
-              Tantalum, Ta                           181
-              Tellurium, Te                          128
-              Terbium, Tb                            159
-              Thallium, Tl                           204
-              Thorium, Th                            232
-              Thulium, Tu                            169
-              Tin, Sn                                119
-              Titanium, Ti                            48
-              Tungsten, W                            184
-              Uranium, U                             238
-              Vanadium, V                             51
-              Xenon, Xe                              131
-              Ytterbium, Yt                          173
-              Yttrium, Y                              89
-              Zinc, Zn                                65
-              Zirconium, Zr                           91
-
-
-                         Table of Geologic Time
-
-            _Eras_
-        _Periods and their              _Important Physical      _Important
-       Duration in Millions                   Events_         Organic Events_
-            of Years_
-
-  Cenozoic
-      Quaternary
-          Recent                        Youthful land forms  Dominance of man.
-                                        having high relief
-                                        formed.
-          Pleistocene Epoch      2 M.Y. Period of            Heidelberg,
-                                        glaciation; four     Neanderthal, and
-                                        great ice advances.  Crô-Magnon man;
-                                                             extinction of
-                                                             large mammals.
-      Tertiary
-          Pliocene Epoch        10 M.Y. Continuing           Intermigration of
-                                        world-wide land      North and South
-                                        elevation.           American mammals.
-                                                             Transformation of
-                                                             ape to man.
-          Miocene Epoch         18 M.Y. Cordilleras, Alps,   Culmination of
-                                        Himalayas formed.    modern types of
-                                        Widespread           mammals. Apes
-                                        vulcanism-basalt     appear in Old
-                                        flows in             World.
-                                        northwestern United
-                                        States.
-          Oligocene Epoch       10 M.Y. Land dominant; seas  Carnivores and
-                                        marginal.            ungulates develop
-                                                             into importance.
-          Eocene Epoch          20 M.Y. Extensive            Dawn of the
-                                        sedimentation; seas  dominance of
-                                        marginal.            mammals. Reptiles
-                                                             subordinate.
-  Cretaceous                    65 M.Y. Widespread           Climax and
-                                        epicontinental       culmination of
-                                        seas. Laramide       reptiles,
-                                        revolution at close  especially
-                                        of period—Rocky      dinosaurs; first
-                                        Mountains formed.    flowering plants
-                                                             and grasses.
-  Mesozoic
-      Jurassic                  38 M.Y. Continent emergent;  Rise of birds and
-                                        shallow seas on      flying reptiles,
-                                        western North        first modern
-                                        America.             trees.
-      Triassic                  35 M.Y. Continent emergent;  Rise of
-                                        seas marginal.       dinosaurs,
-                                                             cycads, and
-                                                             ammonites.
-  Paleozoic
-      Permian                   35 M.Y. World-wide           Extinction of
-                                        continental uplift   most Paleozoic
-                                        and mountain         fauna and flora.
-                                        building.            First modern
-                                        Widespread           insects.
-                                        glaciation.
-      Pennsylvanian             48 M.Y. Continent            Great
-                                        alternately rising   coal-forming
-                                        and sinking.         forests, of ferns
-                                                             and seed-ferns.
-      Mississippian             35 M.Y. Low lands and        Culmination of
-                                        widespread           crinoids,
-                                        submergence.         numerous sharks.
-      Devonian                  40 M.Y. Widespread           First known land
-                                        submergence, local   animals, first
-                                        vulcanism.           forests.
-      Silurian                  28 M.Y. Widespread           First lung fishes
-                                        submergence, local   and scorpions,
-                                        deserts.             abundant corals.
-      Ordovician                65 M.Y. 60% of North         Climax of
-                                        America below sea.   invertebrate
-                                                             dominance, first
-                                                             vertebrate.
-      Cambrian                 105 M.Y. Widespread           First abundant
-                                        submergence.         invertebrate
-                                                             fauna, trilobites
-                                                             dominant.
-  Proterozoic                700 ± M.Y. Long periods of      Bacteria and
-                                        granite intrusion,   seaweeds present.
-                                        sedimentation, and   Most
-                                        mountain building.   invertebrates
-                                                             probably present,
-                                                             but remains are
-                                                             lacking.
-  Archeozoic                 800 ± M.Y. World-wide           Blue-green algae
-                                        intrusive igneous    present,
-                                        activity; some       primitive
-                                        sediments.           one-celled plants
-                                                             and animals
-                                                             probably present.
-
-
-
-
-                              BIBLIOGRAPHY
-
-
-                               MINERALOGY
-
-_Getting Acquainted with Mineralogy._ By G. L. English, 1936,
-    McGraw-Hill Book Co. A beginning textbook of mineralogy.
-
-_Introduction to the Study of Minerals and Rocks._ 3rd Edition, by A. F.
-    Rogers, 1937, McGraw-Hill Book Co. Describes the commoner minerals
-    systematically.
-
-_Dana’s Textbook of Mineralogy._ 4th Edition, revised by W. E. Ford,
-    1932, John Wiley and Sons. Detailed descriptions of minerals, their
-    physical properties, and their occurrence.
-
-_Manual of Mineralogy._ 15th Edition, by E. S. Dana, revised by C. S.
-    Hurlburt, 1941, John Wiley and Sons. A textbook of mineralogy.
-
-
-                     MINERAL ECONOMICS, GEOPOLITICS
-
-_World Minerals and World Peace._ By C. K. Leith, J. W. Furness, and
-    Cleona Lewis, 1943, The Brookings Institution. Physical, economic,
-    and political trends in the mineral industry.
-
-_Minerals in World Affairs._ By T. S. Lovering, 1943, Prentice-Hall.
-
-_Minerals Yearbook._ U. S. Bureau of Mines. An annual volume presenting
-    statistical data on the production of the mineral resources of the
-    United States. Reports on individual minerals or rocks may be had
-    separately.
-
-
-                            ECONOMIC GEOLOGY
-
-_Mineral Deposits._ 4th Edition, by W. Lindgren, 1933, McGraw-Hill Book
-    Co. The manner of occurrence and origin of mineral deposits.
-
-_Elements of Engineering Geology._ 2nd Edition, by H. Ries and T. L.
-    Watson, 1947, John Wiley and Sons.
-
-_This Fascinating Oil Business._ By M. W. Ball, 1940, Bobbs-Merrill Co.
-    A simple and elementary description of the petroleum industry.
-
-_Geology of Coal._ By O. Stutzer and A. C. Noe, 1940, University of
-    Chicago Press.
-
-
-                            GENERAL GEOLOGY
-
-_Down to Earth._ By C. Croneis and W. C. Krumbein, 1936, University of
-    Chicago Press. An introduction to geology, profusely illustrated.
-
-_Textbook of Geology Part I—Physical Geology._ 4th Edition, by C. R.
-    Longwell, A. Knopf, and R. F. Flint, 1939, John Wiley and Sons. A
-    standard text on geology.
-
-_Field Geology._ 4th Edition, by F. H. Lahee, 1941, McGraw-Hill Book Co.
-    Recognition and interpretation of geologic structures and
-    topographic forms as they are observed, and methods of geologic
-    work.
-
-
-                            PRECIOUS STONES
-
-_A Book of Precious Stones._ By J. Wodiska, 1910, G. P. Putnam’s Sons.
-    Written for jewelers, but of general interest.
-
-_The Curious Lore of Precious Stones._ By G. F. Kunz, 1913, Lippincott.
-    Legends and stories of the gem minerals.
-
-_The Magic of Jewels and Charms._ By G. F. Kunz, 1915, Lippincott.
-
-_Popular Gemology._ By R. M. Pearl, 1948, John Wiley and Sons.
-    Scientific and industrial uses of gems, current information about
-    their locality and production.
-
-
-                                FOSSILS
-
-_An Introduction to the Study of Fossils._ By H. W. Shimer, 1933,
-    Macmillan Co. An introductory textbook about fossil plants and
-    animals.
-
-_Invertebrate Paleontology._ By W. H. Twenhofel and R. P. Shrock, 1935,
-    McGraw-Hill Book Co.
-
-_Textbook of Geology Part II—Historical Geology._ 4th Edition, by C.
-    Schuchert and C. O. Dunbar, 1941, John Wiley and Sons. The story of
-    the development of life through the ages.
-
-
-
-
-                                 INDEX
-
-
-                                   A
-  Actinolite, 120
-  Adobe, 210
-  Agate, 107
-  Agate, moss, 73, 108
-  Alabaster, 152
-  Albertite, 229
-  Albite, 110, 113, 115
-  Almandine, 97
-  Almandite, 122, 123
-  Aluminum bronze, 74
-  Aluminum group, 73
-  Amazon stone, 114
-  Amber, 223
-  Amethyst, 104
-  Amethyst, Oriental, 75
-  Amianthus, 120
-  Amphibole group, 119
-  Amygdoloid, 194
-  Amygdoloidal, 176
-  Analcite, 141
-  Andesite, 113, 187
-  Andradite, 122, 124
-  Anglesite, 62
-  Anhydrite, 149
-  Anorthite, 110, 113
-  Anorthosite, 183
-  Anthracite, 218, 222
-  Antimony, 81
-  Antimony, gray, 81
-  Apatite, 160
-  Aquamarine, 125
-  Aragonite, 147
-  Argentite, 35
-  Argillite, 242
-  Arkose, 206
-  Arsenic group, 78
-  Arsenopyrite, 79
-  Asbestos, 120, 140
-  Augite, 118
-  Aventurine, 104
-  Azurite, 46
-
-
-                                    B
-  Barite, 154
-  Barium group, 154
-  Basalt, 188
-  Batholith, 174
-  Bauxite, 77
-  Beryl, 125
-  Beryl, golden, 125
-  Beryllium, 125
-  Bibliography, 270
-  Biotite, 129, 130
-  Bitumen, 228
-  Black jack, 65
-  Bloodstone, 106
-  Bog lime, 213
-  Bombs, 191
-  Boracite, 164
-  Borax, 165
-  Bornite, 41
-  Brass, 64
-  Breccia, 191, 198
-  Brittania metal, 81
-  Bronze, 38
-  Bronze Age, 38
-  Bronzite, 118
-  Bytownite, 113
-
-
-                                    C
-  Calamine, 68
-  Calaverite, 30
-  Calcite, 144
-  Calcium, 143
-  Carbon, 156
-  Carbonite, 222
-  Carbuncle, 124
-  Carnelian, 106
-  Carnotite, 90
-  Cassiterite, 93
-  Cat’s eye, 104
-  Celestite, 153
-  Cerargyrite, 37
-  Cerrusite, 61
-  Ceylonite, 97
-  Chalcedony, 104, 106
-  Chalcocite, 42
-  Chalcopyrite, 40
-  Chalcotrichite, 45
-  Chalk, 213
-  Chert, 107
-  Chlorite, 140
-  Chlorospinel, 98
-  Chromite, 87
-  Chromium, 86
-  Chrysocola, 47
-  Chrysolite, 134, 140
-  Chrysoprase, 106
-  Cinnabar, 91
-  Cinnamon stone, 123
-  Citrine, 103
-  Clay, 207
-  Clay, ball, 208
-  Clay, brick, 209
-  Clay, china, 208
-  Clay, fire, 208
-  Clay, paving brick, 209
-  Clay, sewer-pipe, 209
-  Clay, slip, 209
-  Clay, stoneware, 209
-  Clay stones, 250
-  Cleavage, 21
-  Cleavage, slaty, 234
-  Coal, 217
-  Coal, bituminous, 212, 220
-  Coal, cannel, 221
-  Coal, hard, 222
-  Coal, soft, 220
-  Cobalt, 84
-  Cobalt bloom, 85
-  Cobalt glance, 85
-  Cobalt gray ore, 85
-  Cobaltite, 83
-  Coke, 220
-  Colemanite, 165
-  Collecting, 5, 7
-  Color, 23
-  Concretions, 248
-  Concretions, flint, 253
-  Concretions, lime, 251
-  Concretions, other, 255
-  Concretions, sandstone, 253
-  Conglomerate, 202
-  Copper, 37, 39
-  Copper, blushing, 42
-  Copper, glance, 42
-  Copper, grey, 43
-  Copper, peacock, 42
-  Copper, plush, 45
-  Copper, purple, 41
-  Copper, red, 44
-  Copper, variegated, 42
-  Copper, yellow, 40
-  Coquina, 213
-  Coral, 146
-  Coral rock, 214
-  Corundum, 75
-  Crude oil, 227
-  Cryolite, 78
-  Crystal balls, 101
-  Crystal formation, 14
-  Crystal rock, 103
-  Crystal structure, 11
-  Crystal systems, 13-18
-  Cuprite, 44
-  Cyanite, 128
-
-
-                                    D
-  Dacite, 187
-  Dense, 176
-  Diamond, 157
-  Diamonds, Matura, 127
-  Diamonds, slave’s, 133
-  Diatoms, 231
-  Dikes, 174
-  Diorite, 182
-  Dog-tooth spar, 145
-  Dolomite, 99
-  Dry bone, 68
-
-
-                                    E
-  Earth, diatomaceous, 23
-  Elements, listed, 267
-  Emerald, 125
-  Emerald, Oriental, 75
-  Emery, 76
-  Enstatite, 117
-  Epidote, 134
-  Equipment, 7
-  Erubescite, 42
-  Extrusive, 173
-
-
-                                    F
-  Feldspar, 110
-  Feldspar, alkalic, 111
-  Felsite, 186
-  Felsitic, 176
-  Ferromanganese, 70
-  Flagstone, 207
-  Flint, 106
-  Fluorine, 162
-  Fluorite, 162
-  Fossils, 266
-  Fragmental, 176
-  Franklinite, 69
-  Freestone, 207
-
-
-                                    G
-  Gabbro, 183
-  Galena, 60
-  Garnet group, 121
-  Garnet, Sirian, 123
-  Geodes, 255
-  German silver, 82
-  Gilsonite, 229
-  Glassy, 176
-  Glucinum, 125
-  Gneiss, 237
-  Goethite, 51, 52
-  Gold, 31
-  Gold foil, 64
-  Gold group, 29
-  Gossan, 50
-  Granite, 178
-  Granite, graphic, 179
-  Granitoid, 176
-  Graphite, 156, 219
-  Gravel, 201
-  Graywacke, 206
-  Grit, 206
-  Grossularite, 122, 123
-  Guano, 230
-  Gumbo, 210
-  Gypsum, 150
-
-
-                                    H
-  Halite, 163
-  Hardness, 20
-  Hardpan, 216
-  Heavy spar, 154
-  Heliotrope, 106
-  Hematite, 53
-  Hemihedral forms, 19
-  Hercynite, 98
-  Hexagonal system, 18
-  Hornblende, 121
-  Hornstone, 107
-  Hyacinth, 127
-  Hypersthene, 118
-
-
-                                    I
-  Ice, 167
-  Iceland spar, 145
-  Ice stone, 78
-  Ilmenite, 94
-  Intrusive, 174
-  Iron, 47
-  Iron, bog, 50
-  Iron, chromic, 87
-  Iron, magnetic, 54
-  Iron pyrites, 56
-  Iron, spathic, 55
-  Iron, specular, 53
-  Isometric system, 13
-
-
-                                    J
-  Jacinth, 127
-  Jargons, 127
-  Jargoons, 127
-  Jasper, 106
-  Jet, 222
-
-
-                                    K
-  Kaolin, 137, 208
-  Kaolinite, 137
-
-
-                                    L
-  Labels, 5
-  Labradorite, 113, 116
-  Laccolith, 174
-  Lapilli, 191
-  Lava, 173
-  Lead, 59
-  Lead glance, 60
-  Lead, green ore, 63
-  Lead, white ore, 61
-  Lepidolite, 129, 130
-  Lignite, 218, 219
-  Limestone, 212
-  Limestone, encrinal, 214
-  Limestone, hydraulic, 214
-  Limestone, lithographic, 214
-  Limonite, 49, 51
-  Loess, 210
-  Luster, 23
-
-
-                                    M
-  Magma, 173
-  Magnesite, 98
-  Magnesium group, 96
-  Magnetite, 54
-  Malachite, 45
-  Malanite, 124
-  Malta, 229
-  Manganese group, 70
-  Manganite, 72
-  Marble, 243
-  Marble, Suisun, 146
-  Marcasite, 57
-  Marl, 211
-  Mercury, 90
-  Meteorites, 262
-  Mica group, 128
-  Microcline, 113, 114
-  Millerite, 83
-  Mineral tables, 25
-  Minerals, defined, 10
-  Molybdenite, 81
-  Molybdenum, 80
-  Monoclinic system, 17
-  Monzonite, 181
-  Morion, 103
-  Mother-of-pearl, 148
-  Muscovite, 129
-
-
-                                    N
-  Natrolite, 142
-  Natural gas, 227
-  Needle iron stone, 52
-  Niccolite, 83
-  Nickel, copper, 83
-  Nickel group, 82
-
-
-                                    O
-  Obsidian, 191
-  Ochre red, 54
-  Ochre yellow, 49
-  Oligoclase, 113, 115
-  Olivine, 134
-  Olivine-gabbro, 183
-  Onyx, 108
-  Onyx, Californian, 146
-  Onyx marble, 215
-  Onyx, Mexican, 146
-  Oolites, 254
-  Opal, 108
-  Opal-agate, 109
-  Opal, common, 109
-  Opal, fire, 109
-  Opal, precious, 109
-  Ophicalcite, 246
-  Ophiolite, 246
-  Orpiment, 80
-  Orthoclase, 110, 113
-  Orthorhombic system, 16
-
-
-                                    P
-  Paste, 103
-  Pearls, 148
-  Pearlstone, 193
-  Peat, 218, 219
-  Pebbles, 256
-  Pegmatite, 179
-  Peridot, 134
-  Peridotite, 184
-  Perlite, 193
-  Petroleum series, 224, 227
-  Pewter, 60
-  Phenocrysts, 189
-  Phlogopite, 129, 131
-  Phosphate, 160, 230
-  Phosphorus, 159
-  Phyllite, 242
-  Picotite, 97
-  Pisolite, 255
-  Pitchstone, 193
-  Plagioclase, 111
-  Plasma, 106
-  Platinum, 95
-  Plumbago, 156
-  Porous, 176
-  Porphyritic, 176
-  Porphyry, 189
-  Prase, 104
-  Prousite, 36
-  Psilomelane, 72
-  Pumice, 193
-  Pyrargyrite, 35
-  Pyrite, 56
-  Pyrite, capillary, 83
-  Pyrite, magnetic, 58
-  Pyrite, white, 57
-  Pyritohedron, 56, 318
-  Pyrolusite, 71
-  Pyromorphite, 63
-  Pyrope, 122, 123
-  Pyroxene group, 116
-  Pyroxenite, 185
-  Pyrrhotite, 58
-
-
-                                    Q
-  Quartz, 100
-  Quartz-diorite, 181
-  Quartz, milky, 103
-  Quartz, rose, 104
-  Quartz, smoky, 103
-  Quartzite, 239
-  Quicksands, 204
-  Quicksilver, 90
-
-
-                                    R
-  Radium, 89
-  Realgar, 80
-  Rhinestones, 101
-  Rhodochrosite, 73
-  Rhyolite 185
-  Rock, phosphate, 230
-  Rocks, 170
-  Rocks, defined, 10
-  Rocks, igneous, 172
-  Rocks, igneous, classified, 177
-  Rocks, metamorphic, 232
-  Rocks, metamorphic, classified, 236
-  Rocks, sedimentary, 194
-  Rocks, sedimentary, classified, 196
-  Rubicelle, 97
-  Ruby, 75
-  Ruby, Balas, 97
-  Ruby mica, 52
-  Rutile, 94
-
-
-                                    S
-  Salt, 163
-  Sand, 202
-  Sandstone, 205
-  Sapphire, 75
-  Sapphire, Oriental white, 75
-  Sardonyx, 108
-  Satin spar, 146
-  Schist, 240
-  Schistosity, 234
-  Scoria, 192, 193
-  Septeria, 252
-  Sericite, 130
-  Serpentine, 139, 245
-  Shale, 210
-  Shale, oil-bearing, 225
-  Sheet, 173
-  Siderite, 55
-  Silica, 99
-  Silicates, 99
-  Silicon, 99
-  Sill, 174
-  Sillimanite, 128
-  Silver, 34
-  Silver, dark red, 35
-  Silver, German, 65
-  Silver glance, 35
-  Silver group, 32
-  Silver, horn, 37
-  Silver, light red, 36
-  Silver, ruby, 35
-  Sinter, 110
-  Slate, 241
-  Smalt, 84
-  Smaltite, 85
-  Smithsonite, 68
-  Soapstone, 244
-  Sodalite, 126
-  Soil, 198
-  Solder, 60
-  Specific gravity, 22
-  Speigeleisen, 70
-  Spelter, 64
-  Spessartite, 122, 123
-  Sphalerite, 65
-  Spinel, 97
-  Spinel-ruby, 97
-  Stalactites, 146
-  Stalagmites, 146
-  Staurolite, 133
-  Steatite, 244
-  Stellite, 84, 88
-  Stibnite, 81
-  Stilbite, 143
-  Stock, 174
-  Streak, 23
-  Strontianite, 152
-  Strontium group, 152
-  Sulphur, 166
-  Syenite, 180
-  Sylvanite, 30
-
-
-                                    T
-  Talc, 138
-  Talus, 197
-  Tetragonal system, 15
-  Tetrahedrite, 43
-  Tile ore, 45
-  Till, 215
-  Tillite, 217
-  Time chart, 268
-  Tin, 92
-  Tin stone, 93
-  Titanium, 93
-  Tonalite, 181
-  Topaz, 131
-  Topaz, false, 103
-  Topaz, Oriental, 75
-  Topaz, Saxon, 132
-  Topaz, Scotch, 132
-  Topaz, smoky, 132
-  Topaz, Spanish, 132
-  Tourmaline, 135
-  Trachite, 186
-  Trap, 188
-  Travertine, 146, 215
-  Tremolite, 120
-  Triclinic system, 18
-  Tripolite, 110
-  Tufa, calcareous, 147
-  Tuff, 190
-  Tungsten, 87
-  Turgite, 51
-  Turquois, 161
-  Twinning, 19
-  Type metal, 60
-
-
-                                    U
-  Uintaite, 229
-  Uranium, 89
-  Uvarovite, 122, 123
-
-
-                                    V
-  Vanadium, 89
-  Verde antique, 247
-  Volcanic ash, 190
-  Volcanic blocks, 191
-
-
-                                    W
-  Water, 167
-  White metal, 64
-  Willemite, 67
-  Witherite, 153
-  Wolframite, 88
-  Wood, agatized, 108
-  Wood, opalized, 109
-  Wood, silicified, 108
-
-
-                                    X
-  Xanthosiderite, 51
-
-
-                                    Z
-  Zeolites, 141
-  Zinc, 63
-  Zinc blende, 65
-  Zinc red ore, 66
-  Zinc, ruby, 65
-  Zincite, 66
-  Zircon, 127
-
-
-Plate Frontispiece
-
-    [Illustration: Tourmaline crystals, growing amid feldspar crystals
-    in a cavity in granite, from Paris, Me.]
-
-
-Plate 5
-
-    [Illustration: Gold in quartz, from California]
-
-
-Plate 6
-
-    [Illustration: Native silver in calcite]
-
-    [Illustration: Argentite, the black masses throughout the white
-    quartz]
-
-
-Plate 7
-
-    [Illustration: Pyrargyrite as it appears after moderate exposure to
-    the light.]
-
-    [Illustration: Crystal form of Pyrargyrite]
-
-    [Illustration: Prousite as it appears after moderate exposure to the
-    light]
-
-
-Plate 8
-
-    [Illustration: Native copper from Michigan]
-
-    [Illustration: Chalcopyrite in tetrahedrons and an occasional
-    octahedron.]
-
-
-Plate 9
-
-    [Illustration: Chalcocite crystals with the bluish tarnish]
-
-    [Illustration: Tetrahedrite crystals]
-
-
-Plate 11
-
-    [Illustration: Cuprite, the red crystals showing characteristic
-    color, other showing the green tarnish of malachite]
-
-    [Illustration: Malachite (green) and azurite (blue), the two
-    minerals shown together as they very commonly occur]
-
-
-Plate 12
-
-    [Illustration: Limonite]
-
-    [Illustration: The crystal form in which goethite is found, _p_ is
-    the prism faces, _b_ and _c_ are faces formed by beveling the edges
-    of the prism, _o_ is the pyramidal face characteristic of the ends]
-
-
-Plate 13
-
-    [Illustration: Hematite, Clinton iron ore, oolitic]
-
-    [Illustration: Siderite crystals]
-
-
-Plate 15
-
-    [Illustration: Pyrite crystals]
-
-    [Illustration: Marcasite in concretionary form with radiate
-    structure]
-
-
-Plate 17
-
-    [Illustration: Galena in crystals]
-
-    [Illustration: Pyromorphite crystals (green)]
-
-
-Plate 19
-
-    [Illustration: Sphalerite, some the normal yellow and some crystals
-    with the reddish tinge. (White is dolomite)]
-
-    [Illustration: Zincite]
-
-
-Plate 21
-
-    [Illustration: Smithsonite in yellow crystals]
-
-    [Illustration: Franklinite in octahedral crystals]
-
-
-Plate 24
-
-    [Illustration: Arsenopyrite, showing crystals massed so as to be
-    incompletely developed]
-
-    [Illustration: Realgar as it usually occurs in powdery
-    incrustations]
-
-
-Plate 25
-
-    [Illustration: Large crystal of stibnite, the light colored face is
-    the one parallel to which cleavage occurs]
-
-    [Illustration: Niccolite as a vein in slate]
-
-
-Plate 26
-
-    [Illustration: Cobaltite, silver color, with pink tinge]
-
-    [Illustration: Smaltite, pink is cobalt bloom]
-
-
-Plate 27
-
-    [Illustration: Carnotite from southwest Colorado]
-
-    [Illustration: Cinnabar]
-
-
-Plate 31
-
-    [Illustration: Amethyst, not however deep enough colored for gems]
-
-    [Illustration: Jasper, with botryoidal surface]
-
-
-Plate 32
-
-    [Illustration: Banded Agate from Brazil]
-
-
-Plate 33
-
-    [Illustration: Common Opal from Arizona]
-
-    [Illustration: Siliceous sinter or Geyserite from The Yellowstone
-    Park]
-
-
-Plate 35
-
-    [Illustration: A group of Microcline crystals from Pike’s Peak,
-    Colo.]
-
-    [Illustration: Labradorite, showing multiple twinning (the
-    striation), and the iridescent play of colors]
-
-
-Plate 36
-
-    [Illustration: Crystal form of a pyroxene; _a_ and _b_ prism faces,
-    _m_ the beveled edge between two prism faces]
-
-    [Illustration: Cross section of a pyroxene crystal showing the lines
-    of intersection of the two cleavage planes]
-
-    [Illustration: Cross sections of pyroxenes, showing typical forms
-    taken by crystals]
-
-    [Illustration: Augite crystals, in crystalline limestone]
-
-
-Plate 38
-
-    [Illustration: The dodecahedron and the 24-sided figure
-    characteristic of garnets]
-
-    [Illustration: The garnet, grossularite]
-
-    [Illustration: The garnet alamandite]
-
-
-Plate 39
-
-    [Illustration: Beryl of gem quality]
-
-    [Illustration: Zircon in syenite]
-
-
-Plate 40
-
-    [Illustration: Cyanite crystals in schist]
-
-    [Illustration: A crystal of mica, showing basal cleavage]
-
-
-Plate 41
-
-    [Illustration: Crystal form typical of topaz]
-
-    [Illustration: A topaz crystal from Brazil]
-
-    [Illustration: Crystal form typical of staurolite when simple]
-
-    [Illustration: A typical twin of staurolite]
-
-
-Plate 43
-
-    [Illustration: Serpentine]
-
-    [Illustration: Chlorite]
-
-
-Plate 49
-
-    [Illustration: Apatite crystals in crystalline calcite]
-
-    [Illustration: The ends of apatite crystals showing common modes of
-    termination]
-
-
-Plate 50
-
-    [Illustration: A group of fluorite crystals]
-
-    [Illustration: A group of halite crystals]
-
-
-Plate 61
-
-    [Illustration: Amber]
-
-    [Illustration: Two bottles of petroleum, the left hand one with a
-    paraffin base, the right hand one with an asphalt base]
-
-
-Plate 65
-
-    [Illustration: Mica schist, with garnets]
-
-    [Illustration: Chlorite schist]
-
-
-Plate 67
-
-    [Illustration: Serpentine, composed of serpentine, hematite, and
-    some calcite]
-
-
-Plate 1
-
-
-                  Basal forms of the isometric system
-
-    [Illustration: Cube]
-
-    [Illustration: Octahedron]
-
-    [Illustration: Dodecahedron]
-
-
-Plate 2
-
-
-                  Basal forms of the tetragonal system
-
-    [Illustration: A square prism]
-
-    [Illustration: Octahedron]
-
-
-                 Basal forms of the orthorhombic system
-
-    [Illustration: A Rectangular prism]
-
-    [Illustration: Octahedron]
-
-
-Plate 3
-
-
-                  Basal forms of the monoclinic system
-
-    [Illustration: The rectangular prism askew]
-
-    [Illustration: The octahedron]
-
-    [Illustration: A cross section of the prism with its edges beveled
-    so that the _b_ faces are obliterated by the _m_ faces, and a
-    six-sided prism is formed (pseudo-hexagonal)]
-
-    [Illustration: Basal form of the triclinic system]
-
-
-Plate 4
-
-
-                  Basal forms of the hexagonal system
-
-    [Illustration: The six-sided prism]
-
-    [Illustration: The double pyramid]
-
-    [Illustration: The rhombohedron]
-
-
-Plate 10
-
-    [Illustration: Tetrahedrons showing characteristic manner in which
-    tetrahedrite occurs]
-
-    [Illustration: A cube with the edges beveled and the corners cut in
-    a form characteristic of cuprite]
-
-
-Plate 30
-
-    [Illustration: Two intergrowing or twinned quartz crystals]
-
-    [Illustration: Diagram of the typical quartz crystal, _p_ prism
-    faces, _l_ left hand rhombohedron, _r_ right hand rhombohedron]
-
-    [Illustration: A quartz crystal on which the left hand rhombohedron
-    is represented by small faces while the right hand rhombohedron has
-    large faces]
-
-
-Plate 14
-
-    [Illustration: Crystal forms of hematite, _A_ the rhombohedron with
-    the edges beveled; _B_ the tabular form, resulting from the
-    excessive development of the two _o_ faces opposite each other]
-
-    [Illustration: A typical crystal of magnetite]
-
-    [Illustration: The rhombohedron typical of siderite]
-
-
-Plate 16
-
-    [Illustration: The pyritohedron]
-
-    [Illustration: The pyritohedron with certain of its edges beveled by
-    the cube faces, to show the relationship of these two forms]
-
-
-Plate 18
-
-
-                      Typical forms for cerrusite
-
-    [Illustration: The pyramid, _n_ the prism face, _m_ the beveled
-    prism, _p_ the octahedral face, and _o_ the edge of the octahedral
-    faces beveled]
-
-    [Illustration: The simple type of twinning]
-
-    [Illustration: A multiple twin where three crystals grow through
-    each other]
-
-    [Illustration: Forms in which anglesite occurs: _l_ the pyramid
-    face, _p_ the prism face, _o_ the vertical edge of the prism
-    beveled, _m_ the horizontal edge of the prism beveled, _n_ a further
-    beveling of the horizontal edge of the prism. _D_ the tabular, _E_
-    the prismatic form]
-
-
-Plate 20
-
-    [Illustration: A characteristic form in which sphalerite may occur;
-    being the combination of, _d_ the dodecahedron, _o_ the octahedron,
-    and _t_, a 24-sided figure]
-
-    [Illustration: Characteristic form for zincite crystals, _n_ the
-    hexagonal prism, and _p_ pyramidal faces on it]
-
-    [Illustration: Typical form of crystal of willemite: _p_ the prism,
-    _r_ rhombohedron faces on end, ½ _r_ a second lower rhombohedron]
-
-
-Plate 22
-
-    [Illustration: Moss agates, showing the dendritic growth of
-    manganitic minerals, like manganite or pyrolusite]
-
-    [Illustration: Moss agates]
-
-    [Illustration: Crystal form of manganite]
-
-
-Plate 23
-
-    [Illustration: Crystals of green corundum in syenite, from Montana]
-
-    [Illustration: Typical crystal forms of corundum: _A_ the elongated
-    prism with the alternate corners cut by rhombohedral faces, _B_ the
-    tabular prism, _C_ the double pyramid]
-
-
-Plate 28
-
-    [Illustration: Cassiterite, twinned crystals]
-
-    [Illustration: The crystal form in which both cassiterite and rutile
-    occur when in simple crystals, _p_ prism faces, _m_ beveling of the
-    prism, _o_ octahedral face, _n_ beveling of the edge between
-    octahedral faces]
-
-    [Illustration: Multiple twinning characteristic of rutile]
-
-
-Plate 29
-
-    [Illustration: Crystal of Spinel]
-
-
-                 Crystal forms in which dolomite occurs
-
-    [Illustration: _A_ the cleavage form, rhombohedron with the faces
-    curved]
-
-    [Illustration: _B_ the rhombohedron with the corners cut, as it
-    often occurs]
-
-    [Illustration: _C_ the form found in gypsum or anhydrite]
-
-
-Plate 34
-
-    [Illustration: Orthoclase, a cleavage piece, _a_ and _b_ the perfect
-    cleavage planes, and _c_ the imperfect cleavage plane]
-
-
-                      Crystal forms of orthoclase
-
-    [Illustration: _A_ the simple crystal]
-
-    [Illustration: _B_ the twinned form]
-
-    [Illustration: _C_ the twinned form in which the crystals are
-    intergrowing]
-
-    [Illustration: Diagram of a multiple twin of a plagioclase feldspar]
-
-
-Plate 37
-
-
-                     Diagrams of amphibole crystals
-
-    [Illustration: _A_ a typical crystal]
-
-    [Illustration: _B_ cross section showing the intersection of
-    cleavage planes]
-
-    [Illustration: _C_ and _D_ cross sections to show variations in
-    outline]
-
-    [Illustration: Tremolite in silky fibrous crystals. Asbestos]
-
-    [Illustration: Hornblende crystals in quartzite]
-
-
-Plate 42
-
-    [Illustration: Epidote crystals]
-
-    [Illustration: Typical forms of epidote crystals; _p_ prism faces,
-    _m_, _n_, _x_, and _y_ beveled edges of the prism, _o_ octahedral
-    faces]
-
-
-                      Typical forms of tourmaline
-
-    [Illustration: _A_ side view; _B_ and _C_ ends to show terminations;
-    _p_ prism faces, _m_ beveling of prism edges, _r_ a low rhombohedron
-    on the end, _s_ the opposite rhombohedron, _b_ basal face, and the
-    other faces represent bevelings]
-
-
-Plate 48
-
-    [Illustration: A group of barite crystals]
-
-    [Illustration: Outline of the typical tabular barite crystal]
-
-    [Illustration: The six-sided double pyramid, composed of three
-    interpenetrating crystals, typical of witherite and strontianite]
-
-
-Plate 44
-
-    [Illustration: The typical form of analcite]
-
-    [Illustration: A typical natrolite crystal]
-
-    [Illustration: The typical crystal form of stilbite]
-
-    [Illustration: A sheaf-like bundle of fibrous crystals, typical of
-    stilbite]
-
-
-Plate 45
-
-    [Illustration: A group of calcite crystals]
-
-
-                        Typical forms of calcite
-
-    [Illustration: _A_ the rhombohedron formed by cleavage]
-
-    [Illustration: _B_ a rhombohedral crystal truncated by the basal
-    plane]
-
-    [Illustration: _C_ the scalenohedron]
-
-    [Illustration: _D_ the scalenohedron truncated by the rhombohedron]
-
-    [Illustration: _E_ the scalenohedron on a prism]
-
-
-Plate 46
-
-
-                       Typical forms of aragonite
-
-    [Illustration: _A_ the simple crystal]
-
-    [Illustration: _B_ a needle-like form, twinned]
-
-    [Illustration: _C_ cross section to show how the form may appear
-    six-sided]
-
-    [Illustration: Typical form of the anhydrite crystal]
-
-
-Plate 47
-
-    [Illustration: A piece of gypsum looking on the surface of the
-    perfect cleavage, and showing the two other cleavages as lines,
-    intersecting at 66°. Twinning is also shown]
-
-    [Illustration: A simple crystal of gypsum]
-
-    [Illustration: Twin crystals of gypsum]
-
-
-Plate 51
-
-    [Illustration: Sulphur crystals]
-
-    [Illustration: Ice crystals, the top one, the end of a hexagonal
-    prism; the two lower figures multiple twins as in snow flakes]
-
-
-Plate 52
-
-    [Illustration: The Devil’s Tower, Wyoming, an example of igneous
-    rock with columnar structure, and resting on sedimentary rocks.
-    Courtesy of the U. S. Geological Survey]
-
-
-Plate 53
-
-    [Illustration: A coarse granite]
-
-    [Illustration: Graphic granite]
-
-
-Plate 54
-
-    [Illustration: Syenite]
-
-    [Illustration: Gabbro]
-
-
-Plate 55
-
-    [Illustration: Basalt-porphyry. The large white crystals are
-    phenocrysts of plagioclase feldspar]
-
-    [Illustration: Basalt-obsidian]
-
-
-Plate 56
-
-    [Illustration: Amgydoloid]
-
-
-Plate 57
-
-    [Illustration: The north face of Scott’s Bluff, Neb., showing
-    sedimentary sandstones above and clays below. The type of erosion is
-    characteristic of arid regions. Courtesy of the U. S. Geological
-    Survey]
-
-
-Plate 58
-
-    [Illustration: Breccia]
-
-    [Illustration: Conglomerate]
-
-
-Plate 59
-
-    [Illustration: Calcareous shale]
-
-    [Illustration: Coquina]
-
-
-Plate 60
-
-    [Illustration: Foramenifera from Chalk; enlarged about 25 diameters]
-
-    [Illustration: Encrinal Limestone; fragments of the stems, arms and
-    body of Crinoids]
-
-
-Plate 62
-
-    [Illustration: _A_ diatomaceous earth magnified 50 times]
-
-    [Illustration: _B_ and _C_ two diatoms from the above enlarged 250
-    times. After Gravelle, by the courtesy of Natural History]
-
-
-Plate 63
-
-    [Illustration: A metamorphic rock, showing the contortion of layers
-    due to expansion under heat]
-
-
-Plate 64
-
-    [Illustration: A conglomerate partly metamorphosed to a gneiss. Note
-    the flattened pebbles and the alternation of the intermediate
-    material to mica scales, etc.]
-
-    [Illustration: A typical gneiss]
-
-
-Plate 66
-
-    [Illustration: Phyllite]
-
-    [Illustration: A white marble, with black streaks due to graphite]
-
-
-Plate 68
-
-    [Illustration: Claystones, simple and compound]
-
-    [Illustration: A line concretion, which on splitting disclosed a
-    fern leaf of the age of the coal measures]
-
-
-Plate 69
-
-    [Illustration: A septeria from Seneca Lake, N. Y.]
-
-    [Illustration: Pisolite]
-
-
-Plate 70
-
-    [Illustration: A geode filled with quartz crystals]
-
-
-Plate 71
-
-    [Illustration: A quartz pebble from the bed of a New England brook]
-
-    [Illustration: A pebble of schist and granite from the foot of Mt.
-    Toby, Mass.]
-
-
-Plate 72
-
-    [Illustration: An iron-nickel meteorite, of 23 lbs. which fell in
-    Claiborne Co., Tenn.]
-
-    [Illustration: An etched slice of an iron meteorite which fell in
-    Reed City, Osceola Co., Mich.]
-
-
-Plate 73
-
-    [Illustration: A stony meteorite, about natural size, which fell in
-    1875, in Iowa Co., Iowa]
-
-
-                                PUTNAM’S
-                           NATURE FIELD BOOKS
-                      Companion books to this one
-
-  Mathews       American Wild Flowers
-                American Trees and Shrubs
-                Wild Birds and Their Music
-  Durand        Wild Flowers in Homes and Gardens
-                My Wild Flower Garden
-                Common Ferns
-  Lutz          Insects
-  Loomis        Rocks and Minerals
-  Eliot         Birds of the Pacific Coast
-  Armstrong     Western Wild Flowers
-  Alexander     Birds of the Ocean
-  Anthony       North American Mammals
-  Thomas        Common Mushrooms
-  Sturgis       Birds of the Panama Canal Zone
-  Miner         Seashore Life
-  Breder        Marine Fishes of the Atlantic Coast
-  Morgan        Ponds and Streams
-  Longyear      Rocky Mountain Trees and Shrubs
-  Olcott        Field Book of the Skies
-  Putnam
-  Beebe         The Shore Fishes of Bermuda
-  Tee-Van
-  Schrenkeisen  Fresh-Water Fishes of North America North of
-                Mexico
-
-
-
-
-                          Transcriber’s Notes
-
-
-—Retained publication information from the printed edition: this eBook
-  is public-domain in the country of publication.
-
-—In the text versions only, text in italics is delimited by
-  _underscores_.
-
-—Silently corrected a few typos.
-
-—Reconstructed an image caption (Pisolite) on Plate 69.
-
-—Generated a cover image based on elements in the book.
-
-
-
-
-
-
-
-End of the Project Gutenberg EBook of Field Book of Common Rocks and Minerals, by 
-Frederic Brewster Loomis and Walter Everett Corbin
-
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-
-The Project Gutenberg EBook of Field Book of Common Rocks and Minerals, by 
-Frederic Brewster Loomis and Walter Everett Corbin
-
-This eBook is for the use of anyone anywhere in the United States and most
-other parts of the world at no cost and with almost no restrictions
-whatsoever.  You may copy it, give it away or re-use it under the terms of
-the Project Gutenberg License included with this eBook or online at
-www.gutenberg.org.  If you are not located in the United States, you'll have
-to check the laws of the country where you are located before using this ebook.
-
-Title: Field Book of Common Rocks and Minerals
-       For identifying the Rocks and Minerals of the United States
-              and interpreting their Origins and Meanings
-
-Author: Frederic Brewster Loomis
-        Walter Everett Corbin
-
-Release Date: August 18, 2017 [EBook #55382]
-
-Language: English
-
-Character set encoding: UTF-8
-
-*** START OF THIS PROJECT GUTENBERG EBOOK FIELD BOOK OF COMMON ROCKS ***
-
-
-
-
-Produced by Stephen Hutcheson, Dave Morgan and the Online
-Distributed Proofreading Team at http://www.pgdp.net
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-</pre>
-
-<div id="cover" class="img">
-<img id="coverpage" src="images/cover.jpg" alt="Field Book of Common Rocks and Minerals" width="468" height="901" />
-</div>
-<div class="box">
-<h1>Field Book <i>of</i>
-<br />Common Rocks
-<br /><i>and</i> Minerals</h1>
-<hr />
-<p class="center"><b>For identifying the Rocks and Minerals of the United States and interpreting their Origins and Meanings</b></p>
-<hr />
-<p class="center">By
-<br /><span class="large"><b>Frederic Brewster Loomis</b></span>
-<br /><span class="small">Late Professor of Mineralogy and Geology
-<br />in Amherst College</span></p>
-<p class="tbcenter"><span class="small">With 47 Colored Specimens and over 100 other Illustrations from Photographs by W. E. Corbin and drawings by the Author</span></p>
-<p class="tbcenter"><b><span class="large">G. P. Putnam&rsquo;s Sons</span>
-<br />New York and London</b></p>
-</div>
-<p class="center small">FIELD BOOK
-<br />OF
-<br />COMMON ROCKS AND MINERALS</p>
-<p class="center small">Copyright, 1923, 1948
-<br />by
-<br />Frederick Brewster Loomis</p>
-<p class="center small">Twenty-sixth Impression
-<br />Revised 1948</p>
-<p class="center small">All rights reserved. This book, or parts thereof, must not be reproduced in any form without permission.</p>
-<p class="center small">Made in the United States of America</p>
-<p class="tbcenter"><span class="sc">Dedicated</span>
-<br /><span class="small">TO</span>
-<br /><span class="large">MY MOTHER</span>
-<br /><span class="small">WHO ENCOURAGED ME WHILE A BOY TO GATHER MINERALS, ROCKS AND FOSSILS.</span></p>
-<div class="pb" id="Page_vii">vii</div>
-<h2 id="c1"><span class="h2line1">PREFACE</span></h2>
-<p>Everyone, who is alert as he wanders about
-this world, wants to know what he is seeing
-and what it is all about. Here and there with
-the aid of capable guides a few have been introduced
-into the sphere of that wide and fascinating
-knowledge of Nature which has been so rapidly
-accumulated during this and the latter part of
-the last century. It is a full treasure house
-constantly being enriched, but unfortunately the
-few who have been initiated have soon acquired
-a technical language and habit, so that their
-knowledge and new acquisitions are communicated
-to but few. The public at large, not having
-the language nor an interpreter at hand, has
-come almost at once to a barrier which few have
-the time or patience to surmount.</p>
-<p>Latterly it has become clear that the largest
-progress cannot be made if the knowledge of
-any branch of Science is confined to a few only.
-The most rapid advances have been made where
-many men are interested and enthusiastic. In
-no science should there be a difficult barrier
-between the amateur and the professional student.
-All Nature is equally open for everyone
-to study, and there should never be created obstacles
-as by the use of terminology not easily
-acquired by anyone. Of late these barriers have
-<span class="pb" id="Page_viii">viii</span>
-been in part broken down and competent students
-have written guides which anyone can
-follow, and soon begin to know the plants, trees,
-birds, insects, etc. So far no one has attempted
-to make the study of minerals and rocks so direct
-and simple that everyone can get a start. Most
-books on minerals, and practically all those on
-rocks are written for school courses, and to say
-the least chill any enthusiasm which is naturally
-aroused by the finding of interesting looking
-rocks or minerals.</p>
-<p>The purpose of this book is first of all to provide
-a means of identifying minerals and rocks by
-such methods as are practical without elaborate
-equipment or previous training: and second to
-suggest the conditions under which the various
-minerals and rocks were formed, so that, at the
-first contact, one may get a conception of the
-events which have anteceded the mineral or
-rock which has been found. For this purpose
-keys have been worked out for determining the
-rocks and minerals by such obvious features as
-color, hardness, etc. Each mineral or rock is
-introduced by a summary of its characters, then
-the features by which it may be distinguished
-from any other similar mineral are given, after
-which its mode of origin and its meanings are
-considered. For those interested in the composition
-of the minerals, it is given in chemical
-symbols with each mineral. Most classifications
-of minerals are based on the composition, all the
-sulphides, carbonates, etc., being grouped together,
-but in this book, because the popular
-interest and commercial uses are primarily in
-<span class="pb" id="Page_ix">ix</span>
-the metal present, the minerals are grouped in
-each case about the chief metal, all the minerals
-of iron being grouped together, for instance.</p>
-<p>A few minerals and rocks which are not strictly
-common have been included such as gems and
-meteorites; the gems because they are of intense
-interest to their owners and are often simply
-perfect examples of a fairly common mineral;
-and such forms as meteorites because it is important
-that, if one should run across one, it should
-be recognized, and so not lost to the world.</p>
-<p>The book is freely illustrated, those minerals
-in which color is important for identification
-being illustrated in colors, and those which are
-black, or in which the color is not a determining
-factor, are shown in either photographic or
-outline figures.</p>
-<p>In the introductory chapter there are explanations
-of the terms used in describing minerals,
-and of the systems in which they are grouped.
-A knowledge of the systems may not be a
-necessity, but it is a great help in determining
-minerals, and is very important in understanding
-why the individual minerals take the varied
-forms which are characteristic of them. These
-systems will be better understood after a few
-minerals have been gathered and examined.</p>
-<p>It is hoped the book will help those who have
-already some knowledge of rocks and minerals,
-and especially that it will tempt many to begin
-an acquaintance with the rocks and minerals
-which are all about them, and are the foundation
-on which our material progress is built. Rocks
-and minerals have some advantages over most
-<span class="pb" id="Page_x">x</span>
-objects which are collected in that they neither
-require special preparation before they can be
-kept, nor do they deteriorate with time.</p>
-<p>The author will appreciate corrections or
-suggestions as to better presentation of the
-material in this book.</p>
-<p><span class="lr">F. B. L.</span></p>
-<p><span class="sc">Amherst, Mass.</span></p>
-<div class="pb" id="Page_xi">xi</div>
-<h2 class="center">CONTENTS</h2>
-<dl class="toc">
-<dt><span class="small">PAGE</span></dt>
-<dt><a href="#c1"><span class="sc">Preface</span></a> vii</dt>
-<dt class="jl"><span class="small">CHAPTER</span></dt>
-<dt><a href="#c2"><span class="cn">I.&mdash;</span><span class="sc">An Introduction</span></a> 3</dt>
-<dt><a href="#c3"><span class="cn">II.&mdash;</span><span class="sc">On the Forms and Properties of Minerals</span></a> 10</dt>
-<dt><a href="#c4"><span class="cn">III.&mdash;</span><span class="sc">The Minerals</span></a> 25</dt>
-<dt><a href="#c5"><span class="cn">IV.&mdash;</span><span class="sc">The Rocks</span></a> 170</dt>
-<dt><a href="#c6"><span class="cn">V.&mdash;</span><span class="sc">Miscellaneous Rocks</span></a> 248</dt>
-<dt><a href="#c7"><span class="cn">&nbsp;</span><span class="sc">Bibliography</span></a> 270</dt>
-<dt><a href="#c8"><span class="cn">&nbsp;</span><span class="sc">Index</span></a> 273</dt>
-</dl>
-<div class="pb" id="Page_xiii">xiii</div>
-<h2><span class="h2line1">LIST OF PLATES</span>
-<br /><span class="h2line2">(AT END OF BOOK)</span></h2>
-<dl class="toc">
-<dt><span class="small">PAGE</span></dt>
-<dt><a href="#Plate_Frontispiece">Tourmaline crystals, growing amid feldspar crystals in a cavity in granite, from Paris, Me.</a> 279</dt>
-<dt><a href="#Plate_1"><span class="sc">Plate</span> 1.&mdash;Basal forms of the isometric system</a> 311</dt>
-<dt><a href="#Plate_2"><span class="sc">Plate</span> 2.&mdash;Basal forms of the tetragonal system. Basal forms of the orthorhombic system</a> 312</dt>
-<dt><a href="#Plate_3"><span class="sc">Plate</span> 3.&mdash;Basal forms of the monoclinic system. A cross section of the prism with its edges beveled so that a six-sided prism is formed (pseudo-hexagonal). Basal form of the triclinic system.</a> 313</dt>
-<dt><a href="#Plate_4"><span class="sc">Plate</span> 4.&mdash;Basal forms of the hexagonal system</a> 314</dt>
-<dt><a href="#Plate_5"><span class="sc">Plate</span> 5.&mdash;Gold in quartz from California (<i>in color</i>)</a> 280</dt>
-<dt><a href="#Plate_6"><span class="sc">Plate</span> 6.&mdash;Native silver in calcite. Argentite, the black masses throughout the white quartz (<i>in color</i>)</a> 281</dt>
-<dt><a href="#Plate_7"><span class="sc">Plate</span> 7.&mdash;Pyrargyrite as it appears after moderate exposure to the light; streak at left. Crystal form of pyrargyrite. Prousite as it appears after moderate exposure to the light; streak at left (<i>in color</i>)</a> 282</dt>
-<dt><a href="#Plate_8"><span class="sc">Plate</span> 8.&mdash;Native copper from Michigan. Chalcopyrite in tetrahedrons and an occasional octahedron; streak to the left (<i>in color</i>)</a> 283</dt>
-<dt><a href="#Plate_9"><span class="sc">Plate</span> 9.&mdash;Chalcocite crystals with the bluish tarnish. Tetrahedrite crystals; streak to left (<i>in color</i>)</a> 284</dt>
-<dt><a href="#Plate_10"><span class="sc">Plate</span> 10.&mdash;Tetrahedrons showing characteristic manner in which tetrahedrite occurs. A cube with the edges beveled and the corners cut in a form characteristic of cuprite</a> 315</dt>
-<dt><a href="#Plate_11"><span class="sc">Plate</span> 11.&mdash;Cuprite, the red crystals showing characteristic color, others showing the green tarnish of malachite. Malachite (green) and azurite (blue), the two minerals shown together as they very commonly occur (<i>in color</i>)</a> 285</dt>
-<dt><a href="#Plate_12"><span class="sc">Plate</span> 12.&mdash;Limonite. The crystal form in which goethite is found (<i>in color</i>)</a> 286</dt>
-<dt><a href="#Plate_13"><span class="sc">Plate</span> 13.&mdash;Hematite. Clinton iron ore, oolitic. Siderite crystals (<i>in color</i>)</a> 287</dt>
-<dt><a href="#Plate_14"><span class="sc">Plate</span> 14.&mdash;Crystal forms of hematite. A typical crystal of magnetite. The rhombohedron typical of siderite</a> 317</dt>
-<dt><a href="#Plate_15"><span class="sc">Plate</span> 15.&mdash;Pyrite crystals. Marcasite in concretionary form with radiate structure (<i>in color</i>)</a> 288</dt>
-<dt><a href="#Plate_16"><span class="sc">Plate</span> 16.&mdash;The pyritohedron. The pyritohedron with certain of its edges beveled by the cube faces, to show the relationship of these two forms</a> 318</dt>
-<dt><a href="#Plate_17"><span class="sc">Plate</span> 17.&mdash;Galena in crystals. Pyromorphite crystals (Green) (<i>in color</i>)</a> 289</dt>
-<dt><a href="#Plate_18"><span class="sc">Plate</span> 18.&mdash;Typical forms for cerrusite. Forms in which anglesite occurs</a> 319</dt>
-<dt><a href="#Plate_19"><span class="sc">Plate</span> 19.&mdash;Sphalerite, some the normal yellow and some crystals with the reddish tinge. (White is dolomite.) Zincite, streak to the left (<i>in color</i>)</a> 290</dt>
-<dt><a href="#Plate_20"><span class="sc">Plate</span> 20.&mdash;A characteristic form in which sphalerite may occur. Characteristic form for zincite crystals. Typical form of crystal of willemite</a> 320</dt>
-<dt><a href="#Plate_21"><span class="sc">Plate</span> 21.&mdash;Smithsonite in yellow crystals. Franklinite in octahedral crystals, streak to left (<i>in color</i>)</a> 291</dt>
-<dt><a href="#Plate_22"><span class="sc">Plate</span> 22.&mdash;Moss agates, showing the dendritic growth of manganitic minerals, like manganite or pyrolusite. Crystal form of manganite</a> 321</dt>
-<dt><a href="#Plate_23"><span class="sc">Plate</span> 23.&mdash;Crystals of green corundum in syenite, from Montana. Typical crystal forms of corundum</a> 322</dt>
-<dt><a href="#Plate_24"><span class="sc">Plate</span> 24.&mdash;Arsenopyrite, showing crystals massed so as to be incompletely developed. Realgar as it usually occurs in powdery incrustations (<i>in color</i>)</a> 292</dt>
-<dt><a href="#Plate_25"><span class="sc">Plate</span> 25.&mdash;Large crystals of stibnite; the light colored face is the one parallel to which cleavage occurs. Niccolite is a vein in slate (<i>in color</i>)</a> 293</dt>
-<dt><a href="#Plate_26"><span class="sc">Plate</span> 26.&mdash;Cobaltite, silver color, with pink tinge. Smaltite, pink is cobalt bloom (<i>in color</i>)</a> 294</dt>
-<dt><a href="#Plate_27"><span class="sc">Plate</span> 27.&mdash;Carnotite from Southwest Colorado. Cinnabar (<i>in color</i>)</a> 295</dt>
-<dt><a href="#Plate_28"><span class="sc">Plate</span> 28.&mdash;Cassiterite, twinned crystals. The crystal form in which both cassiterite and rutile occur when in simple crystals. Multiple twinning characteristic of rutile</a> 323</dt>
-<dt><a href="#Plate_29"><span class="sc">Plate</span> 29.&mdash;Crystal of spinel. Crystal forms in which dolomite occurs</a> 324</dt>
-<dt><a href="#Plate_30"><span class="sc">Plate</span> 30.&mdash;Two intergrowing or twinned quartz crystals. Diagram of the typical quartz crystal. A quartz crystal on which the left hand rhombohedron is represented by small faces, while the right hand rhombohedron has large faces</a> 316</dt>
-<dt><a href="#Plate_31"><span class="sc">Plate</span> 31.&mdash;Amethyst, not however deep enough colored for gems. Jasper, with botryoidal surface (<i>in color</i>)</a> 296</dt>
-<dt><a href="#Plate_32"><span class="sc">Plate</span> 32.&mdash;Banded agate from Brazil (<i>in color</i>)</a> 297</dt>
-<dt><a href="#Plate_33"><span class="sc">Plate</span> 33.&mdash;Common opal from Arizona. Siliceous sinter or geyserite from Yellowstone Park (<i>in color</i>)</a> 298</dt>
-<dt><a href="#Plate_34"><span class="sc">Plate</span> 34.&mdash;Orthoclase, a cleavage piece. Crystal forms of orthoclase. Diagram of a multiple twin of a plagioclase feldspar</a> 325</dt>
-<dt><a href="#Plate_35"><span class="sc">Plate</span> 35.&mdash;A group of microcline crystals from Pike&rsquo;s Peak, Colo. Labradorite, showing multiple twinning (the striation) and the iridescent play of colors (<i>in color</i>)</a> 299</dt>
-<dt><a href="#Plate_36"><span class="sc">Plate</span> 36.&mdash;Crystal form of a pyroxene. Cross sections of a pyroxene crystal showing the lines of intersection of two cleavage planes. Cross sections of pyroxenes, showing typical forms taken by crystals. Augite crystals, in crystalline limestone (<i>in color</i>)</a> 300</dt>
-<dt><a href="#Plate_37"><span class="sc">Plate</span> 37.&mdash;Diagrams of amphibole crystals. Tremolite in silky fibrous crystals, asbestos. Hornblende crystals in quartzite</a> 326</dt>
-<dt><a href="#Plate_38"><span class="sc">Plate</span> 38.&mdash;The dodecahedron and the 24-sided figure characteristic of garnets. The garnet, grossularite. The garnet, alamandite (<i>in color</i>)</a> 301</dt>
-<dt><a href="#Plate_39"><span class="sc">Plate</span> 39.&mdash;Beryl of gem quality. Zircon in syenite (<i>in color</i>)</a> 302</dt>
-<dt><a href="#Plate_40"><span class="sc">Plate</span> 40.&mdash;Cyanite crystals in schist. A crystal of mica, showing basal cleavage (<i>in color</i>)</a> 303</dt>
-<dt><a href="#Plate_41"><span class="sc">Plate</span> 41.&mdash;Crystal form typical of topaz. A topaz crystal from Brazil. Crystal form typical of staurolite when simple. A typical twin of staurolite (<i>in color</i>)</a> 304</dt>
-<dt><a href="#Plate_42"><span class="sc">Plate</span> 42.&mdash;Epidote crystals. Typical forms of epidote crystals. Typical forms of tourmaline</a> 327</dt>
-<dt><a href="#Plate_43"><span class="sc">Plate</span> 43.&mdash;Serpentine. Chlorite (<i>in color</i>)</a> 305</dt>
-<dt><a href="#Plate_44"><span class="sc">Plate</span> 44.&mdash;The typical form of analcite. A typical natrolite crystal. The typical crystal form of stilbite. A sheaf-like bundle of fibrous crystals, typical of stilbite</a> 329</dt>
-<dt><a href="#Plate_45"><span class="sc">Plate</span> 45.&mdash;A group of calcite crystals. Typical forms of calcite</a> 330</dt>
-<dt><a href="#Plate_46"><span class="sc">Plate</span> 46.&mdash;Typical forms of aragonite. Typical form of the anhydrite crystal</a> 331</dt>
-<dt><a href="#Plate_47"><span class="sc">Plate</span> 47.&mdash;A piece of gypsum looking on the surface of the perfect cleavage, and showing the two other cleavages as lines, intersecting at 66&deg;. Twinning is also shown. A simple crystal of gypsum. Twin crystals of gypsum.</a> 332</dt>
-<dt><a href="#Plate_48"><span class="sc">Plate</span> 48.&mdash;A group of barite crystals. Outline of the typical tabular barite crystal. The six-sided double pyramid, composed of three interpenetrating crystals, typical of witherite and strontianite</a> 328</dt>
-<dt><a href="#Plate_49"><span class="sc">Plate</span> 49.&mdash;Apatite crystals in crystalline calcite. The ends of apatite crystals showing common modes of termination (<i>in color</i>)</a> 306</dt>
-<dt><a href="#Plate_50"><span class="sc">Plate</span> 50.&mdash;A group of fluorite crystals. A group of halite crystals (<i>in color</i>)</a> 307</dt>
-<dt><a href="#Plate_51"><span class="sc">Plate</span> 51.&mdash;Sulphur crystals. Ice crystals, the top one, the end of a hexagonal prism; the two lower figures multiple twins as in snow flakes</a> 333</dt>
-<dt><a href="#Plate_52"><span class="sc">Plate</span> 52.&mdash;The Devil&rsquo;s Tower, Wyoming, an example of igneous rock with columnar structure, and resting on sedimentary rocks</a> 334</dt>
-<dd>Courtesy of the U. S. Geological Survey</dd>
-<dt><a href="#Plate_53"><span class="sc">Plate</span> 53.&mdash;A coarse granite. Graphic granite</a> 335</dt>
-<dt><a href="#Plate_54"><span class="sc">Plate</span> 54.&mdash;Syenite. Gabbro</a> 336</dt>
-<dt><a href="#Plate_55"><span class="sc">Plate</span> 55.&mdash;Basalt-porphyry. The large white crystals are phenocrysts of plagioclase feldspar. Basalt-obsidian</a> 337</dt>
-<dt><a href="#Plate_56"><span class="sc">Plate</span> 56.&mdash;Amgydoloid</a> 338</dt>
-<dt><a href="#Plate_57"><span class="sc">Plate</span> 57.&mdash;The north face of Scott&rsquo;s Bluff, Neb., showing sedimentary sandstones above and clays below. The type of erosion is characteristic of arid regions</a> 339</dt>
-<dd>Courtesy of the U. S. Geological Survey</dd>
-<dt><a href="#Plate_58"><span class="sc">Plate</span> 58.&mdash;Breccia. Conglomerate</a> 340</dt>
-<dt><a href="#Plate_59"><span class="sc">Plate</span> 59.&mdash;Calcareous shale. Coquina</a> 341</dt>
-<dt><a href="#Plate_60"><span class="sc">Plate</span> 60.&mdash;Foramenifera from chalk; enlarged about 25 diameters. Encrinal limestone; fragments of the stems, arms and body of crinoids</a> 342</dt>
-<dt><a href="#Plate_61"><span class="sc">Plate</span> 61.&mdash;Amber. Two bottles of petroleum, the left hand one with a paraffin base, the right hand one with an asphalt base (<i>in color</i>)</a> 308</dt>
-<dt><a href="#Plate_62"><span class="sc">Plate</span> 62.&mdash;Diatomaceous earth magnified 50 times. Two diatoms from the above enlarged 250 times</a> 343</dt>
-<dd>After Gravelle, by the courtesy of Natural History</dd>
-<dt><a href="#Plate_63"><span class="sc">Plate</span> 63.&mdash;A metamorphic rock, showing the contortion of layers due to expansion under heat</a> 344</dt>
-<dt><a href="#Plate_64"><span class="sc">Plate</span> 64.&mdash;A conglomerate partly metamorphosed to a gneiss. A typical gneiss</a> 345</dt>
-<dt><a href="#Plate_65"><span class="sc">Plate</span> 65.&mdash;Mica schist, with garnets. Chlorite schist (<i>in color</i>)</a> 309</dt>
-<dt><a href="#Plate_66"><span class="sc">Plate</span> 66.&mdash;Phyllite. A white marble, with black streaks due to graphite</a> 346</dt>
-<dt><a href="#Plate_67"><span class="sc">Plate</span> 67.&mdash;Serpentine composed of serpentite, hematite, and some calcite (<i>in color</i>)</a> 310</dt>
-<dt><a href="#Plate_68"><span class="sc">Plate</span> 68.&mdash;Claystones, simple and compound. A lime concretion, which on splitting disclosed a fern leaf of the age of the coal measures</a> 347</dt>
-<dt><a href="#Plate_69"><span class="sc">Plate</span> 69.&mdash;A septeria from Seneca Lake, N. Y. Pisolite from Nevada</a> 348</dt>
-<dt><a href="#Plate_70"><span class="sc">Plate</span> 70.&mdash;A geode filled with quartz crystals</a> 349</dt>
-<dt><a href="#Plate_71"><span class="sc">Plate</span> 71.&mdash;A quartz pebble from the bed of a New England brook. A pebble of schist and granite from the foot of Mt. Toby, Mass.</a> 350</dt>
-<dt><a href="#Plate_72"><span class="sc">Plate</span> 72.&mdash;An iron-nickel meteorite, of 23 lbs., which fell in Claiborne Co., Tenn. An etched slice of an iron meteorite which fell in Reed City, Osceola, Co., Mich.</a> 351</dt>
-<dt><a href="#Plate_73"><span class="sc">Plate</span> 73.&mdash;A stone meteor, about natural size, which fell in 1875 in Iowa Co., Iowa</a> 352</dt>
-</dl>
-<div class="pb" id="Page_xix">xix</div>
-<h1 title="">FIELD BOOK OF
-<br />COMMON ROCKS AND MINERALS</h1>
-<div class="pb" id="Page_3">3</div>
-<h2 id="c2"><span class="h2line1">CHAPTER I</span>
-<br /><span class="h2line2">AN INTRODUCTION</span></h2>
-<h3>Why</h3>
-<p>Why should one be interested in
-rocks and minerals? Because the
-whole world is made of rocks and minerals.
-They are the foundations on which we build.
-From them we draw all our metals, and the
-extent to which we utilize our minerals is a
-measure of the advance of our civilization. Fragments
-of rock are the soil from which, by way
-of the plants, we draw our food, and ultimately
-our life. The rocks make wild or gentle scenery,
-one at least of the sources of pleasure. Knowledge
-of rocks and minerals is then knowledge of
-fundamentals, of ultimate sources. Between
-finding the raw materials and their present uses
-there are usually many steps (so many that we
-forget that the beginning and end are united),
-as for instance in your watch. It is made of gold,
-brass, steel, agate, glass, and perhaps has luminous
-radium paint on the hands. It is a long way
-from finding and mining gold, chalcopyrite,
-hematite, carnotite, etc., through the raw materials,
-gold, copper, iron, etc., to the finished
-watch, but the minerals are the foundations of
-the watch; and it took centuries to find them and
-learn one by one how to use them, from the gold
-<span class="pb" id="Page_4">4</span>
-10,000 years ago down to the radium within the
-last fifty years. Then too there is joy in going
-out into Nature&rsquo;s wild and raw places, joy in
-being on the foundations of the earth, joy in the
-scenery, in the beauty of the minerals themselves.</p>
-<p>But why collect the rocks and minerals? First
-because this is the way to know them. Both
-mineral and rocks require careful examination
-in order to see all those fine points by which they
-are distinguished. It is often necessary to
-compare one with another to get in mind the
-differences of form, color, streak, though with
-increasing familiarity these characteristics are
-recognized at first sight. It is the repeated
-examination which makes a rock tell the story
-of the country from which it came. Our first
-attempts to read the story give us only the most
-general facts. Nature&rsquo;s book, written in the
-rocks, has to be read closely, often between the
-lines. Until we are used to the characters in
-which the words are written, we read slowly.
-When they look at Nature&rsquo;s book, always open,
-most people do not read; for they do not know
-their letters. Every mineral is a letter, every
-rock a word, and we learn to read as we learn the
-minerals and rocks, and every time we go over
-them we get more facts coming out. The place
-where a rock or mineral occurs is of course the
-relation between them, and is involved in reading
-the story. No one today is a perfect reader.
-We are all learning to see more in the rocks day
-by day. So it is important to have the rocks
-and minerals where they can be handled and
-<span class="pb" id="Page_5">5</span>
-repeatedly examined, where we can turn to them
-in our leisure moments. Don&rsquo;t stop when you
-have learned the name of a mineral or rock.
-You need more. See what it means. Secondly,
-minerals have beauties of form, color, and structure,
-and they do not fade. They will be as
-perfect in ten years as when found. We are all
-naturally crows, and love to gather the objects
-which interest us. It is not a bad habit, and only
-needs directing. Cultivate it. Have a hobby,
-and minerals and rocks are a good one; for they
-are like treasures in Heaven which &ldquo;neither moth
-nor rust doth corrupt.&rdquo; Not only will they give
-you pleasure, but they will be a constructive
-education, training the eye to see, and the mind
-to think straight. No one ever regretted the
-time and effort spent in collecting either minerals
-or rocks.</p>
-<h3>Collecting</h3>
-<p>In order to make a collection valuable
-two or three rules must be observed.
-In the case of rocks, collect large enough
-samples so that they will be characteristic, and
-clear in their make-up. The standard size for
-rocks is 3 &times; 4 inches on top and one to two inches
-thick according to the nature of the rock. Tiny
-fragments do not give the character of the rock
-as well, and they are all the time getting into
-confusion. <b>Every specimen should be labeled</b>,
-with at least its name and the exact locality from
-which it came. Composition, structural features,
-associations, and classification may be added, the
-more the better; for each item adds to the information
-and interest of the specimen. One may
-<span class="pb" id="Page_6">6</span>
-make his own labels or have printed blanks,
-and may put as much care and art into the
-labels as desired, the more the better. One thing
-is very important and that is to have a number
-on the label with a corresponding one on the
-specimen, so that in case they should get separated,
-they may be readily brought together,
-even by one who is not familiar with the individual
-specimens. Lastly, give your collection
-as good a place as possible, either in drawers,
-boxes or in a case. The specimens are worth
-being kept in order and where they can be readily
-seen and compared. Nature is systematic, and
-there is a reason for the order in which rocks and
-minerals are taken up. It is desirable either that
-this order, or some one of the orders of Nature
-appear in the collection. In this book the metals
-are the basis of classification, all those minerals
-primarily related to one of the metals being
-grouped together.</p>
-<p>In collecting minerals, the size of the specimens
-can not be so regularly followed, but it
-should be followed when collecting non-crystalline
-minerals, and when possible. Crystals
-however are chosen from a variety of points of
-view, as perfection of form, color, examples of
-cleavage, twinning, etc.; so that in many cases
-smaller or larger examples must appear in the
-collection. It is always desirable that as many
-variations of a rock or mineral as possible should
-appear in the collection, and in many cases
-examples of the matrix from which the crystals
-came. When crystals are tiny, it is well to place
-them in vials, that they may not be lost.</p>
-<div class="pb" id="Page_7">7</div>
-<h3>Where</h3>
-<p>Where shall we start in making a
-collection? Near home. Get the
-local minerals and rocks first, and then range as
-widely as possible. The best places are bare and
-exposed rocks, especially where fresh and un-weathered
-surfaces are available. Quarries and
-where there has been blasting along roads offer
-fine opportunities. Fissures and cavities in the
-rocks are especially likely to have fine crystals,
-and in all localities continued search will reveal
-a surprising number of different minerals. The
-greatest variety occur in metamorphic rocks, or
-where igneous rocks come in contact with other
-rocks, but even the sedimentary rocks have a
-goodly range of minerals. All through the
-glaciated regions of the northern United States
-lie scattered boulders brought from afar, which
-will yield a surprising number of minerals and
-variety of rocks.</p>
-<h3>Equipment</h3>
-<p>One may start with a very simple
-equipment, a geologist&rsquo;s or stone
-mason&rsquo;s hammer which can be obtained at any
-hardware store, being sufficient for field work.
-Rocks should be broken, so as to show fresh
-surfaces and to get below the disintegrating
-effects of weathering. At home one should have
-a streak plate (a piece of unglazed porcelain), a
-set of hardness minerals (see <a href="#Page_20">page 20</a>), and a
-small bottle each of hydrochloric and nitric acid.
-A pocket lens is useful in order to see more clearly
-the form of small minerals. These things can be
-purchased of any Naturalist&rsquo;s Supply Co., like
-Ward&rsquo;s Natural Science Establishment, P.O. 24,
-<span class="pb" id="Page_8">8</span>
-Beachwood Sta., Rochester, N. Y., or the Kny-Scheerer
-Corp., 483 First Ave., New York City.
-Success depends upon a quick eye, and persistent
-hunting. When traveling, opportunities
-are offered at frequent intervals to see and get
-new specimens.</p>
-<h3>Study Your Collection</h3>
-<p>Be sure and see the meaning in
-each rock and mineral. The history
-of the country is revealed in its
-rocks and minerals. Note whether the rocks are
-horizontal or folded, whether they change character
-from place to place, or vertically. In going
-over a piece of country you may locate an ancient
-mountain system now leveled, by noting a
-series of metamorphic rocks, with a central core
-of granite, the roots of former mountains. Don&rsquo;t
-be afraid to draw conclusions from what you see.
-Later, when the opportunity offers, look up the
-region in the geological folio, bulletin, or map of
-that section, and check up your findings. These
-geological folios and bulletins, of which there is
-one for nearly every region, are a great help to
-collectors in suggesting where to look for various
-rocks and minerals. Write to the Director of
-the U. S. Geological Survey, Washington, D. C.,
-for a catalogue of the publications of the United
-States Survey, or find out from him what are the
-maps or folios for the region in which you are
-interested. These U. S. publications cost but
-little. When opportunity presents itself, visit
-other collections. In them you will see some of
-the minerals or rocks which have puzzled you,
-and there is nothing quite so satisfactory as
-<span class="pb" id="Page_9">9</span>
-seeing the rocks or minerals themselves. No
-description can always be so convincing. Then
-too you will get suggestions as to localities that
-you can visit.</p>
-<h3>Literature</h3>
-<p>As your collection grows, if you
-find you have special interest in one
-or another branch of the field, you can get books
-giving more details in that line; and at the back
-of this book will be found a list of such books.</p>
-<div class="pb" id="Page_10">10</div>
-<h2 id="c3"><span class="h2line1">CHAPTER II</span>
-<br /><span class="h2line2">ON THE FORMS AND PROPERTIES OF MINERALS</span></h2>
-<h3>Rocks</h3>
-<p>All we know of the earth by direct
-observation is confined to less than
-four miles depth; though by projecting downward
-the layers of rock that come to the surface, we
-may fairly assume a knowledge of the structure
-down to six or eight miles depth. This outer
-portion is often referred to as the &ldquo;crust of the
-earth,&rdquo; but the idea that the deeper portions are
-molten is no longer held. This outer portion is
-made of rocks, and a rock may be defined as, <i>a
-mass of material, loose or solid, which makes up an
-integral part of the earth</i>, as granite, limestone, or
-sand. The rocks (except glassy igneous ones)
-are aggregates of one or more minerals; either in
-their original form like the quartz, feldspar and
-mica of granite, or in a secondary grouping,
-resulting from the units having been dislodged
-from their primary position and regrouped a
-second time, as in sandstone or clay.</p>
-<h3>Minerals</h3>
-<p>Since the rocks are aggregates of
-minerals, it is best to take up the
-minerals first. A mineral may be defined as <i>a
-natural inorganic substance of definite chemical
-composition</i>. It is usually solid, generally has
-<span class="pb" id="Page_11">11</span>
-crystalline structure, and may or may not be
-bounded by crystal faces. <i>A crystal is a mineral,
-bounded by symmetrically grouped faces, which
-have definite relationships to a set of imaginary
-lines called axes.</i> There are between 1100 and
-1200 minerals, of which 30 are so frequently
-present, and so dominant in making up the rocks,
-that they are termed <i>rock-forming minerals</i>.
-About 150 more occur frequently enough so that
-they can be termed common minerals, and one
-may expect to find a fairly large proportion of
-them. Some of these are abundant in one part
-of the country and rare in others, but this book is
-written to cover the United States, and so all
-those which have a fair abundance are included,
-though some will only be found in the west and
-others mostly in the east. Then there are some
-more minerals which are really rare, but which
-are cherished because of their beauty of color,
-and are used as gems. These are mentioned, and
-many of the gems are simply clear and beautiful
-examples of minerals, which in dark or cloudy
-forms are much more common. If one finds any
-of these rare minerals which are not mentioned
-in this book, he must turn to one of the larger
-mineralogies mentioned in the literature list to
-determine them.</p>
-<h3>Crystal Structure</h3>
-<p>A crystal is a mass of molecules,
-all of the same composition. A molecule
-in its turn is made up of atoms,
-and each atom is a unit mass of an element.
-Thus the calcite molecule is made up of one
-unit or atom of calcium, one of carbon, and three
-<span class="pb" id="Page_12">12</span>
-of oxygen (CaCO&#8323;). These atoms are held together
-by an attraction, and make a molecule,
-and for the study of minerals the molecule is the
-unit. The mineral, calcite, is a mass of molecules
-all like the one above, and each molecule
-so small as to be invisible even with the aid of the
-most powerful microscope. When calcite is in
-crystal form, the molecules, like ranks of soldiers,
-are arranged each in its place, each at a definite
-distance from the other. While each molecule
-may vibrate or wiggle within certain limits it
-does not leave its place. (The comparison with
-soldiers is a good one for the molecules of one
-layer, but it must be remembered that in a
-crystal there are also like spacings and ranks up
-and down as well.) As long as the molecules
-remain in fixed ranks, up and down, forward and
-back, and sideways, the crystal is perfect. Calcite
-may be heated until it melts and becomes
-liquid. Then the molecules leave their definite
-arrangement and move about in all sorts of directions,
-like the soldiers after ranks have broken.
-So long as the molecules are thus free to move
-about but keep together, the substance is a
-liquid. There are cases when the molecules in
-this disorder take fixed positions without falling
-into ranks. Such minerals are non-crystalline
-and usually appear glassy. If still greater heat
-is applied to the mineral in liquid form, a point
-is reached (the vapor point), above which the
-molecules go flying away from each (like soldiers
-in a panic), each seeking to get as far from the
-other as possible, so only a container will prevent
-their dissipation. When in this condition a
-<span class="pb" id="Page_13">13</span>
-mineral is gaseous. When cooled, the reverse
-order obtains. The molecules of gas gather into
-a miscellaneous mob or liquid: and if this is
-further cooled (but not too suddenly), they fall
-into ranks and make a crystal. This may be
-illustrated with water. When above 212&deg; F. it is
-steam (molecules wildly dissipated); when between
-212&deg; and 32&deg; it is water (molecules close
-to each other, but milling like a herd of cattle);
-and when below 32&deg; it is ice, the molecules ranged
-in perfect order, rank on rank.</p>
-<h3>Crystal Systems</h3>
-<p>With all the possible forms that
-crystals can and do take, there are
-six systems of arrangement. First
-there is the case where ranks, files, and vertical
-rows are all equal, and now to be scientific, instead
-of talking about ranks, files, etc., we use
-the term axes to express these ideas; the files or
-arrangements from front to back, being called
-the <i>a axis</i>, the ranks, or side to side arrangement
-the <i>b axis</i>, and the vertical arrangement
-the <i>c axis</i>. (See <a href="#Plate_1">Plate 1</a>.) These axes are imaginary
-lines, but they represent real forces.</p>
-<h3>Isometric system</h3>
-<p>When the axes are all equal and
-at right angles to each other, a
-crystal is said to be in the <b>isometric
-system</b>. The cube is the basal form
-and each side is known as a face. The ends
-of the axes come to the middle of the cube
-faces. The essential feature of this system is
-that whatever happens to one axis must happen
-to all, which is another way of saying that all
-<span class="pb" id="Page_14">14</span>
-the axes are equal. If we think of the cube as
-having the corners cut off, we would have a new
-face on each of the eight corners, in addition
-to the six cube faces. Then if each of these
-new faces were enlarged until they met and
-obliterated the cube faces, an eight-sided figure,
-the octahedron, would result. In this the axes
-would ran to the corners. Another modification
-of the cube would be to bevel each of its twelve
-edges, making twelve new faces in addition to
-the six cube faces. If we think of these new
-faces being developed until they meet and
-obliterate the cube faces, there will result a
-twelve-sided figure, the dodecahedron. And
-the 24 edges of the dodecahedron could be
-beveled to make a 24-sided figure, and so on.
-Of course in Nature the corners are not cut, nor
-the edges beveled, but as a result of the interaction
-of the forces expressed by the axes and
-the distribution of the molecules, the molecules
-arrange themselves in a cube, octahedron, dodecahedron
-or combination of these basal forms.</p>
-<h3>Crystal formation</h3>
-<p>Crystals are formed in liquids as
-they cool or evaporate and can no
-longer hold the minerals in solution.
-Crystals start about a center or nucleus, and
-molecule by molecule, the orderly arrangement
-is increased and the crystal grows, there being
-no size which is characteristic. If free in the
-liquid the crystal grows perfectly on all sides, but
-if crystals are growing side by side, there comes a
-time when they interfere with each other. Then
-the free faces continue to grow and the orderly
-<span class="pb" id="Page_15">15</span>
-internal arrangement is maintained, though
-externally there is interference.</p>
-<h3>Tetragonal system</h3>
-<p>In the second or <b>tetragonal system</b>
-one axis (the c axis) is different from
-the other two, but all three are still
-at right angles with each other. This is saying
-scientifically that the lines of force are greater
-or less in one direction than in the other two, but
-they act at right angles to each other. The a
-and the b axes are equal and anything that
-happens to one of these two must happen to the
-other, but need not happen to the c axis. Thinking
-of the molecules that arrange themselves
-under this system of forces, it is clear that the
-simplest form will be a square prism, <i>i.e.</i>, front
-to back, and from side to side the numbers of
-molecules will be equal, but up and down there
-will be a greater or lesser number. If the eight
-corners of this prism were cut, and these corner
-faces increased in size until they met, the resulting
-octahedron would be longer (or shorter) from
-top to bottom than from side to side or front to
-back, but the measurement from front to back
-would be equal to the one from side to side. In
-this system we may have the vertical edges of the
-prism beveled, and not have to bevel the horizontal
-ones, or we may bevel the horizontal edges
-and not the vertical ones. There is no dodecahedron
-in this system or in any other system
-than the isometric. The forms in this tetrahedral
-system are really a combination of the four
-sides of the square prism with such modifications
-as equally affect them all, with two ends which
-<span class="pb" id="Page_16">16</span>
-may be flat, or pyramidal, or modified pyramidal
-faces.</p>
-<h3>Orthorhombic system</h3>
-<p>The third system has all three axes
-unequal, but all three are still at
-right angles with each other. This
-is saying that the lines of force in the crystals
-are all at right angles to each other but of unequal
-value. The faces in this case are all in
-pairs. What happens at one end of an axis
-must happen at the opposite end, but does not
-need to happen at the ends of any of the other
-axes. We are dealing with pairs of faces (one
-at either end of an axis), and if three such
-pairs are combined in the simplest manner, the
-resulting figure will be a rectangular prism. If
-we cut the eight corners of this prism and enlarge
-the faces until they meet, the result is
-an octahedron, in which the distance from top
-to bottom, from side to side, or from front to
-back is not the same in any two cases. (See
-<a href="#Plate_2">Plate 2</a>.) In this system if a face is made by
-beveling one edge of the prism there must be a
-corresponding face on the edge diagonally
-opposite, but there does not have to be one on
-any of the other edges. However if a corner is
-cut, that face affects all the axes and so all the
-corners must be cut. A great many crystals
-occur in this system, and some of them which
-are prismatic in shape may give trouble, for it is
-not uncommon for the vertical edges of the prism
-to be so beveled, that two of the original prism
-faces are obliterated, and the two remaining faces
-added to the four new faces make a six-sided
-prism, which at first glance seems to belong to the
-<span class="pb" id="Page_17">17</span>
-hexagonal system. (See <a href="#Plate_3">Plate 3</a>, fig. 3.) Close
-examination however will show that, instead of
-all the prism faces being alike, as would be
-necessary for the hexagonal system, they are
-really in pairs, and one pair at least will be
-distinguished in some way, such as being striated,
-pitted, or duller.</p>
-<h3>Monoclinic system</h3>
-<p>The fourth system has all the axes
-unequal, the a axis and the b axis
-at right angles to each other, but
-the c axis is inclined to the a axis, meeting it
-at some other than a right angle. The <b>monoclinic
-system</b> is like the orthorhombic system
-except that it leans, or is askew, in one direction.
-The result is that the faces at the ends
-of the b axis are rhombohedral, while the others
-are rectangular. As in the foregoing system,
-the faces are in pairs at opposite ends of the
-axes; and as in the orthorhombic system, a
-face may occur on one edge and only have to
-be repeated on the edge diagonally opposite.
-The simplest form in this system will be made
-by combining the three pairs of faces at the
-opposite ends of the axes, which gives a prism,
-which is rectangular in cross section, but leans
-backward (or forward) if placed on end. As
-in all the systems, if a corner is cut, all must
-be cut; and if these corner faces are extended
-to meet each other, an octahedron results, in
-which, as in the prism, no two axes are equal.
-If this octahedron is properly orientated (<i>i.e.</i>
-with the a and b axes horizontal), it will lean
-forward or backward. Many minerals belong to
-<span class="pb" id="Page_18">18</span>
-this system; and, as in the orthorhombic system,
-it is not uncommon to have the vertical edges so
-beveled that two of the prism faces are obliterated,
-and the remaining two prism faces with
-the four new faces make a six-sided prism, which
-seems hexagonal. (See <a href="#Plate_3">plate 3</a>, figure 3.) However,
-such a pseudo-hexagonal prism may be
-recognized by at least one pair of the faces having
-distinguishing marks (stri&aelig;, pits, or dullness),
-instead of all being just alike.</p>
-<h3>Triclinic system</h3>
-<p>The fifth or <b>triclinic system</b> has
-all the axes unequal, and no two of
-them intersect at right angles. As
-in the two preceding systems the faces occur
-in pairs at the opposite ends of the axes. This
-is the most difficult system in which to orientate
-a crystal, but fortunately only a few crystals
-occur in this system, such as the feldspars.</p>
-<h3>Hexagonal system</h3>
-<p>Lastly there is a group of crystals
-which have four axes, one vertical,
-and three in the horizontal plane
-which intersect each other at angles of 60&deg;,
-all these three being equal to each other, but
-different from the vertical axis. The simplest
-form in this system is the six-sided prism. If
-one corner of this prism is cut all must be,
-and if these corner faces are extended to meet
-each other, a double-six-sided pyramid results.
-In this system if one of the vertical edges of
-the prism is beveled, all must be, but the horizontal
-edges need not be; or the horizontal edges
-may be beveled and the vertical ones not. The
-ends as they are related to the c axis may be
-<span class="pb" id="Page_19">19</span>
-developed independently of the prism, and so
-the prism may be simply truncated by a flat end,
-or have pyramids on either end.</p>
-<h3>Hemihedral forms</h3>
-<p>In this system it is quite common
-to have forms which result from the
-development of each alternate face of
-either the prism or the double pyramid. In the
-case of the prism, if every alternate face is developed
-(and the others omitted) a three-sided
-prism results, as in tourmaline. In the case of
-the double pyramid if the three alternate faces
-above are united with the three alternate faces
-below, a six-sided figure is formed, which is
-known as the rhombohedron, as all the faces are
-rhombohedral in out-line and all equal. These
-forms in which only half the faces are developed
-are known as <b>hemihedral forms</b>. The same sort
-of thing may happen in the isometric system in
-the case of the octahedron, and also in the case
-of the octahedron of other systems. When half
-the faces of the octahedron are developed, two
-above unite with two below and make a four-sided
-figure, known as a tetrahedron. (See <a href="#Plate_10">plate 10</a>.)
-While tetrahedrons may occur in any of
-the first five systems they are not common outside
-the isometric system.</p>
-<h3>Twinning</h3>
-<p>Another modification of the simple
-forms which will be met occasionally
-is <b>twinning</b>. By this is meant two crystals
-growing together as though placed side by side
-on some one of the faces, and then revolved until
-the two axes which would normally be parallel
-are at some definite angle with each other, 60&deg;, or
-<span class="pb" id="Page_20">20</span>
-180&deg; which is commoner. The surface of contact
-between the two crystals is called the <i>composition
-face</i>, and as no more material can be added on
-that face the crystals continue to grow developing
-the other faces, and we find faces in contact
-with each other which should be at the opposite
-end or other side of the crystals. This contact of
-faces which should not come in contact, and the
-presence of reentrant angles are indications of
-twinning. In some minerals the twinning may
-be repeated time and again, and if the twinning
-is on one of the end faces a branching structure
-results, as in frost and snow crystals, or the
-multiple twinning may be of crystals growing
-side by side when the final form will approximate
-a series of thin sheets placed side by side as in
-some feldspars. The peculiar forms characteristic
-of individual minerals are taken up under
-the respective minerals.</p>
-<p>Other important properties of minerals are
-hardness, cleavage, specific gravity, streak, luster,
-and color.</p>
-<h3>Hardness</h3>
-<p><b>Hardness</b> may be defined as the
-mineral&rsquo;s resistance to abrasion or
-scratching. It is measured by comparing a
-mineral with Moh&rsquo;s scale, a set of ten minerals
-arranged in the order of increasing hardness, as
-follows:</p>
-<dl class="undent"><dt>1 <a href="#species_Talc">talc</a></dt>
-<dt>2 <a href="#species_Gypsum">gypsum</a></dt>
-<dt>3 <a href="#species_Calcite">calcite</a></dt>
-<dt>4 <a href="#species_Fluorite">fluorite</a></dt>
-<dt>5 <a href="#species_Apatite">apatite</a></dt>
-<dt>6 <a href="#species_Feldspar">feldspar</a></dt>
-<dt>7 <a href="#species_Quartz">quartz</a></dt>
-<dt>8 <a href="#species_Topaz">topaz</a></dt>
-<dt>9 <a href="#species_Corundum">corundum</a></dt>
-<dt>10 <a href="#species_Diamond">diamond</a></dt></dl>
-<div class="pb" id="Page_21">21</div>
-<p>A set for measuring hardness may be purchased
-from any dealer in mineral supplies. For rough
-determination, as in the field, the following
-objects have the hardness indicated; the finger
-nail 2&frac14;, a penny 3, a knife blade about 5.5, and
-glass not over 6. In testing, a mineral is harder
-than the one it will scratch, and softer than the
-one by which it is scratched. For instance, if a
-mineral will scratch calcite and is scratched by
-fluorite, it is between 3 and 4 in hardness, say
-3.5. When two samples mutually scratch each
-other they are of equal hardness. Care must be
-used in determining hardness, especially with the
-harder minerals; for often, when testing a mineral,
-the softer one will leave a streak of powder
-on the harder one, which is not a scratch. One
-should always rub the mark to make sure it is
-really a groove made by scratching.</p>
-<h3>Cleavage</h3>
-<p><b>Cleavage</b> is the tendency, characteristic
-of most minerals, and due
-to the arrangement of their molecules, to cleave
-or break along definite planes. The cleavage of
-any mineral is not irregular or indefinite, but
-characteristic for each mineral, and always
-parallel to possible or actual faces on the crystal,
-and always so described. For instance galena
-has three cleavages, all equally good, and
-parallel to the cube faces; so it is said to have
-cubic cleavage. In the same way fluorite has
-octahedral cleavage, and calcite rhombic cleavage.
-In some minerals cleavage is well developed
-in one plane, and less developed in other
-planes, or it may be lacking altogether. The
-<span class="pb" id="Page_22">22</span>
-varying degrees of perfection by which a
-mineral cleaves are expressed as, perfect
-or imperfect, distinct or indistinct, good or
-poor, etc.</p>
-<h3>Specific gravity</h3>
-<p>The <b>specific gravity</b> of a mineral
-is its weight compared with the
-weight of an equal volume of water,
-and is therefore the expression of how many
-times as heavy as water the mineral is. For
-instance the specific gravity of pyrite is 5.1,
-which is saying it is 5.1 times as heavy as
-water. In a pure mineral the specific gravity
-is constant, and an important factor in making
-final determinations. As ordinarily obtained,
-a piece of pure mineral is weighed in air,
-which value may be called x. It is then immersed
-in water and again weighed, and this
-value is called y. The difference between the
-weight in air and that in water is the weight
-of an equal volume of water. Then we have
-the following formula:</p>
-<div class="center">specific gravity = <table class="inline"><tr><td>x</td></tr><tr><td class="ol">x-y</td></tr></table>.</div>
-<p>Various balances have been devised for making
-these measurements, but any balance which will
-weigh small objects accurately, may be adapted
-to specific gravity work, by hanging a small pan
-under the regular weighing pan. When using
-this balance, care is taken to see that the lower
-pan is always submerged in water, even while
-the mineral is being weighed in air, so that
-when weighed in water in the lower pan,
-the weight of this lower pan has already been
-considered.</p>
-<div class="pb" id="Page_23">23</div>
-<h3>Streak</h3>
-<p>By <b>streak</b> is meant the color of the
-mineral when powdered. For some
-minerals, especially metallic ores, it is of great
-importance, for it remains constant, though the
-color of the surface of the mineral changes
-materially. It is most readily determined by
-rubbing a corner of the mineral on a piece of
-unglazed porcelain. Small plates, known as
-&ldquo;streak plates&rdquo; are made for this purpose.</p>
-<h3>Luster</h3>
-<p>The <b>luster</b> of a mineral is the
-appearance of its surface by reflected
-light, and it is an important aid in determining
-many minerals. Two types of luster are
-recognized; metallic, the luster of metals, most
-sulphides and some oxides, all of which are
-opaque on their thin edges; and non-metallic,
-the luster of minerals which are more or less
-transparent on their thin edges, and most of
-which are light colored. The common non-metallic
-lusters are; vitreous, the luster of glass;
-resinous, the appearance of resin; greasy,
-oily appearance; pearly, the appearance of
-mother-of-pearl; silky, like silk due to the
-fibrous structure; adamantine, brilliant like a
-diamond; and dull, as is chalk.</p>
-<h3>Color</h3>
-<p>When used with caution <b>color</b> is
-of the utmost importance in determining
-minerals, especially in making rapid
-determinations. In metallic minerals it is constant
-and dependable; but in the non-metallic
-minerals it may vary, due to the presence of
-small amounts of impurities which act as pigments.
-<span class="pb" id="Page_24">24</span>
-Color depends on chemical composition,
-and when not influenced by impurities is termed
-<i>natural</i>; but when the color is due to some inclosed
-impurity it is termed <i>exotic</i>. In this latter
-case caution must be used in making determinations.
-Many minerals are primarily colorless,
-but take on exotic colors as a result of the
-presence of small quantities of impurities; for
-instance, pure corundum is colorless, but with a
-trace of iron oxide present becomes red, and is
-called the ruby, or with a trace of cobalt becomes
-blue and is called sapphire.</p>
-<div class="pb" id="Page_25">25</div>
-<h2 id="c4"><span class="h2line1">CHAPTER III</span>
-<br /><span class="h2line2">THE MINERALS</span></h2>
-<h4>KEY TO THE MINERALS, BASED ON HARDNESS, COLOR, ETC.</h4>
-<table class="center" summary="">
-<tr class="th"><th colspan="5">OPAQUE COLORS</th></tr>
-<tr class="th"><th><span class="sc">Color</span> </th><th><span class="sc">Hardness</span> </th><th><span class="sc">Streak</span> </th><th><span class="sc">Remarks</span> </th><th><span class="sc">Mineral</span></th></tr>
-<tr><td class="l">Red</td></tr>
-<tr><td class="l"><span class="hst">scarlet</span> </td><td class="l">2.5 </td><td class="l">scarlet </td><td class="l">surface tarnishes black </td><td class="l"><a href="#species_Prousite">prousite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2.5 </td><td class="l">vermilion </td><td class="l">surface scarlet to dark red </td><td class="l"><a href="#species_Cinnabar">cinnabar</a></td></tr>
-<tr><td class="l"><span class="hst">ochre</span> </td><td class="l">7 </td><td class="l">white </td><td class="l">non-crystalline </td><td class="l"><a href="#species_Jasper">jasper</a></td></tr>
-<tr><td class="l"> </td><td class="l">6 </td><td class="l">ochre red </td><td class="l">color red to almost black </td><td class="l"><a href="#species_Hematite">hematite</a></td></tr>
-<tr><td class="l"><span class="hst">rose</span> </td><td class="l">4 </td><td class="l">white </td><td class="l">effervesces in warm acid </td><td class="l"><a href="#species_Rhodochrosite">rhodochrosite</a></td></tr>
-<tr><td class="l"><span class="hst">dark</span> </td><td class="l">4 </td><td class="l">orange </td><td class="l"> </td><td class="l"><a href="#species_Zincite">zincite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2.5 </td><td class="l">purplish red </td><td class="l">surface tarnishes black </td><td class="l"><a href="#species_Pyrargyrite">pyrargyrite</a></td></tr>
-<tr><td class="l"><span class="hst">brownish</span> </td><td class="l">3.5 </td><td class="l">brownish red </td><td class="l"> </td><td class="l"><a href="#species_Cuprite">cuprite</a></td></tr>
-<tr><td class="l">Orange </td><td class="l">3.5 </td><td class="l">white to yellowish </td><td class="l"> </td><td class="l"><a href="#species_Pyromorphite">pyromorphite</a></td></tr>
-<tr><td class="l"> </td><td class="l">1-1&frac12; </td><td class="l">orange </td><td class="l"> </td><td class="l"><a href="#species_Realgar">realgar</a></td></tr>
-<tr><td class="l">Blue </td><td class="l">5.5-6 </td><td class="l">white </td><td class="l">in igneous rocks </td><td class="l"><a href="#species_Sodalite">sodalite</a></td></tr>
-<tr><td class="l"><span class="hst">azure</span> </td><td class="l">4 </td><td class="l">azure </td><td class="l"> </td><td class="l"><a href="#species_Azurite">azurite</a></td></tr>
-<tr><td class="l"><span class="hst">sky</span> </td><td class="l">7 &amp; 4.5 </td><td class="l">white </td><td class="l">blade-like crystals </td><td class="l"><a href="#species_Cyanite">cyanite</a></td></tr>
-<tr><td class="l"><span class="hst">turquoise</span> </td><td class="l">6 </td><td class="l">blue </td><td class="l">non-crystalline </td><td class="l"><a href="#species_Turquois">turquois</a></td></tr>
-<tr><td class="l"> </td><td class="l">2-4 </td><td class="l">white </td><td class="l"> </td><td class="l"><a href="#species_Chrysocolla">chrysocolla</a></td></tr>
-<tr><td class="l">Green</td></tr>
-<tr><td class="l"><span class="hst">malachite</span> </td><td class="l">3.5 </td><td class="l">lighter green </td><td class="l"> </td><td class="l"><a href="#species_Malachite">malachite</a></td></tr>
-<tr><td class="l"><span class="hst">olive</span> </td><td class="l">6.5-7 </td><td class="l">white </td><td class="l">in igneous rocks </td><td class="l"><a href="#species_Olivine">olivine</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5 </td><td class="l">white to yellow </td><td class="l"> </td><td class="l"><a href="#species_Pyromorphite">pyromorphite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2 </td><td class="l">white </td><td class="l">mica-like cleavage </td><td class="l"><a href="#species_Chlorite">chlorite</a></td></tr>
-<tr><td class="l"> </td><td class="l">1 </td><td class="l">white </td><td class="l">greasy feel, color light to dark olive green </td><td class="l"><a href="#species_Talc">talc</a></td></tr>
-<tr><td class="l"><span class="hst">yellowish</span> </td><td class="l">6.5 </td><td class="l">white </td><td class="l"> </td><td class="l"><a href="#species_Epidote">epidote</a></td></tr>
-<tr><td class="l"> </td><td class="l">2.5-4 </td><td class="l">white </td><td class="l">color yellow green to olive </td><td class="l"><a href="#species_Serpentine">serpentine</a></td></tr>
-<tr><td class="l">Yellow</td></tr>
-<tr><td class="l"><span class="hst">golden</span> </td><td class="l">2.5 </td><td class="l">shining </td><td class="l">non-crystalline </td><td class="l"><a href="#species_Gold">gold</a></td></tr>
-<tr><td class="l"><span class="hst">brassy</span> </td><td class="l">6 </td><td class="l">greenish-black </td><td class="l">usually crystalline </td><td class="l"><a href="#species_Pyrite">pyrite</a></td></tr>
-<tr><td class="l"> </td><td class="l">6 </td><td class="l">greenish-gray </td><td class="l">color pale brassy yellow, usually non-crystalline </td><td class="l"><a href="#species_Marcasite">marcasite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">greenish-black </td><td class="l">colors nitric acid green </td><td class="l"><a href="#species_Millerite">millerite</a></td></tr>
-<tr><td class="l"> </td><td class="l">4 </td><td class="l">greenish-black </td><td class="l">color golden similar to gold </td><td class="l"><a href="#species_Chalcopyrite">chalcopyrite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5 </td><td class="l">dark brown </td><td class="l">purplish tarnish on surface </td><td class="l"><a href="#species_Tetrahedrite">tetrahedrite</a></td></tr>
-<tr><td class="l"><span class="hst">bronze</span> </td><td class="l">5.5 </td><td class="l">pale brownish-black </td><td class="l">color with coppery cast </td><td class="l"><a href="#species_Niccolite">niccolite</a></td></tr>
-<tr><td class="l"> </td><td class="l">4 </td><td class="l">dark gray-black </td><td class="l">with speedy black tarnish </td><td class="l"><a href="#species_Pyrrhotite">pyrrhotite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3 </td><td class="l">gray-black </td><td class="l">brownish with bluish tarnish </td><td class="l"><a href="#species_Bornite">bornite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2.5 </td><td class="l">shining </td><td class="l">coppery red color </td><td class="l"><a href="#species_Copper">copper</a></td></tr>
-<tr><td class="l"><span class="hst">sulphur</span> </td><td class="l">3.5 </td><td class="l">white to yellowish </td><td class="l">compact masses </td><td class="l"><a href="#species_Pyromorphite">pyromorphite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2 </td><td class="l">yellow </td><td class="l"> </td><td class="l"><a href="#species_Sulphur">sulphur</a></td></tr>
-<tr><td class="l"> </td><td class="l">1-3 </td><td class="l"> </td><td class="l">earthy masses </td><td class="l"><a href="#species_Carnotite">carnotite</a></td></tr>
-<tr class="pbtr"><td colspan="5">
-</td></tr>
-<tr><td class="l">Brown</td></tr>
-<tr><td class="l"><span class="hst">violet</span> </td><td class="l">1&frac12; </td><td class="l">shining </td><td class="l">tarnishes black </td><td class="l"><a href="#species_Cerargyrite">cerargyrite</a></td></tr>
-<tr><td class="l"><span class="hst">yellowish</span> </td><td class="l">7.5 </td><td class="l">white </td><td class="l">4-sided prisms </td><td class="l"><a href="#species_Zircon">zircon</a></td></tr>
-<tr><td class="l"> </td><td class="l">6.5 </td><td class="l">gray </td><td class="l"> </td><td class="l"><a href="#species_Cassiterite">cassiterite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">ochre yellow </td><td class="l">compact to earthy masses </td><td class="l"><a href="#species_Limonite">limonite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5 </td><td class="l">brownish-yellow </td><td class="l"> </td><td class="l"><a href="#species_Goethite">goethite</a></td></tr>
-<tr><td class="l"> </td><td class="l">4.5 </td><td class="l">black </td><td class="l"> </td><td class="l"><a href="#species_Wolframite">wolframite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5 </td><td class="l">yellowish-brown </td><td class="l"> </td><td class="l"><a href="#species_Sphalerite">sphalerite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5 </td><td class="l">white </td><td class="l"> </td><td class="l"><a href="#species_Siderite">siderite</a></td></tr>
-<tr><td class="l"><span class="hst">grayish</span> </td><td class="l">7.5 </td><td class="l">white </td><td class="l">often twinned </td><td class="l"><a href="#species_Staurolite">staurolite</a></td></tr>
-<tr><td class="l"> </td><td class="l">6.5 </td><td class="l">pale brown </td><td class="l"> </td><td class="l"><a href="#species_Rutile">rutile</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5 </td><td class="l">white to yellowish </td><td class="l">earthy masses </td><td class="l"><a href="#species_Pyromorphite">pyromorphite</a></td></tr>
-<tr><td class="l"><span class="hst">reddish</span> </td><td class="l">7 </td><td class="l">white </td><td class="l">dodecahedrons &amp; trapezohedrons </td><td class="l"><a href="#species_Garnet">garnet</a></td></tr>
-<tr><td class="l">Black </td><td class="l">6.5 </td><td class="l">gray </td><td class="l"> </td><td class="l"><a href="#species_Cassiterite">cassiterite</a></td></tr>
-<tr><td class="l"> </td><td class="l">6 </td><td class="l">reddish-brown </td><td class="l"> </td><td class="l"><a href="#species_Franklinite">franklinite</a></td></tr>
-<tr><td class="l"> </td><td class="l">6 </td><td class="l">black </td><td class="l">magnetic </td><td class="l"><a href="#species_Magnetite">magnetite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">dark brown </td><td class="l"> </td><td class="l"><a href="#species_Chromite">chromite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">black </td><td class="l">yellow precipitate in sulphuric acid </td><td class="l"><a href="#species_Wolframite">wolframite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5-6 </td><td class="l">black </td><td class="l">non-magnetic </td><td class="l"><a href="#species_Ilmenite">ilmenite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5-6 </td><td class="l">brownish-black </td><td class="l">compact masses </td><td class="l"><a href="#species_Psilomelane">psilomelane</a></td></tr>
-<tr><td class="l"> </td><td class="l">5 </td><td class="l">brownish-yellow </td><td class="l">surface often brownish </td><td class="l"><a href="#species_Goethite">goethite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5 </td><td class="l">dark brown </td><td class="l">tetrahedrons </td><td class="l"><a href="#species_Tetrahedrite">tetrahedrite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2.5 </td><td class="l">silvery </td><td class="l">fresh surfaces silver color </td><td class="l"><a href="#species_Silver">silver</a></td></tr>
-<tr><td class="l"> </td><td class="l">2.5 </td><td class="l">scarlet </td><td class="l">fresh surfaces bright red </td><td class="l"><a href="#species_Prousite">prousite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2.5 </td><td class="l">purplish red </td><td class="l">fresh surfaces red </td><td class="l"><a href="#species_Pyrargyrite">pyrargyrite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2 </td><td class="l">black </td><td class="l">earthy masses </td><td class="l"><a href="#species_Pyrolusite">pyrolusite</a></td></tr>
-<tr><td class="l"> </td><td class="l">1 </td><td class="l">steel gray </td><td class="l">greasy feel </td><td class="l"><a href="#species_Graphite">graphite</a></td></tr>
-<tr><td class="l">Metallic Gray </td><td class="l">2.5 </td><td class="l">black </td><td class="l">tarnishes black, bluish, or green </td><td class="l"><a href="#species_Chalcocite">chalcocite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2.5 </td><td class="l">lead gray </td><td class="l">sectile </td><td class="l"><a href="#species_Argentite">argentite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2.5 </td><td class="l">lead gray </td><td class="l">cubic cleavage </td><td class="l"><a href="#species_Galena">galena</a></td></tr>
-<tr><td class="l"> </td><td class="l">2 </td><td class="l">lead gray </td><td class="l">long prismatic crystals </td><td class="l"><a href="#species_Stibnite">stibnite</a></td></tr>
-<tr><td class="l"> </td><td class="l">1.5 </td><td class="l">bluish gray </td><td class="l">in scales </td><td class="l"><a href="#species_Molybdenite">molybdenite</a></td></tr>
-<tr><td class="l"><span class="hst">steel</span> </td><td class="l">5.5 </td><td class="l">gray black </td><td class="l">rose color in nitric acid </td><td class="l"><a href="#species_Smaltite">smaltite</a></td></tr>
-<tr><td class="l"> </td><td class="l">4.5 </td><td class="l">steel gray </td><td class="l">very heavy </td><td class="l"><a href="#species_Platinum">platinum</a></td></tr>
-<tr><td class="l"> </td><td class="l">4 </td><td class="l">reddish black </td><td class="l">often in striated prisms </td><td class="l"><a href="#species_Manganite">manganite</a></td></tr>
-<tr><td class="l"> </td><td class="l">1 </td><td class="l">gray </td><td class="l">with greasy feel </td><td class="l"><a href="#species_Graphite">graphite</a></td></tr>
-<tr><td class="l"><span class="hst">silvery</span> </td><td class="l">5.5 </td><td class="l">black </td><td class="l"> </td><td class="l"><a href="#species_Arsenopyrite">arsenopyrite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2.5 </td><td class="l">silvery </td><td class="l">tarnishes black on exposure </td><td class="l"><a href="#species_Silver">silver</a></td></tr>
-<tr><td class="l"><span class="hst">reddish</span> </td><td class="l">5.5 </td><td class="l">gray black </td><td class="l">rose color in nitric acid </td><td class="l"><a href="#species_Cobaltite">cobaltite</a></td></tr>
-<tr><td class="l"><span class="hst">pearly</span> </td><td class="l">1-1&frac12; </td><td class="l">shining </td><td class="l">exposed surfaces violet brown </td><td class="l"><a href="#species_Cerargyrite">cerargyrite</a></td></tr>
-<tr><td class="l">White, with impurities </td><td class="l">4 </td><td class="l">white </td><td class="l">porcelainous masses, effervesces in acid </td><td class="l"><a href="#species_Magnesite">magnesite</a></td></tr>
-<tr><td class="l"><span class="hst">grayish or yellowish</span> </td><td class="l">2 </td><td class="l">white </td><td class="l">earthy masses, greasy feel </td><td class="l"><a href="#species_Kaolinite">kaolinite</a></td></tr>
-<tr><td class="l"> </td><td class="l">1-3 </td><td class="l">white </td><td class="l">earthy masses </td><td class="l"><a href="#species_Bauxite">bauxite</a></td></tr>
-<tr><td class="l"> </td><td class="l">1 </td><td class="l">white </td><td class="l">greasy feel, fibrous or scaly </td><td class="l"><a href="#species_Talc">talc</a></td></tr>
-</table>
-<div class="pb" id="Page_27">27</div>
-<table class="center" summary="">
-<tr class="th"><th colspan="4">TRANSPARENT OR TRANSLUCENT COLORS</th></tr>
-<tr class="th"><th><span class="sc">Color</span> </th><th><span class="sc">Hardness</span> </th><th><span class="sc">Remarks</span> </th><th><span class="sc">Mineral</span></th></tr>
-<tr><td colspan="4" class="l">Colorless or with faint tinges of color due to impurities</td></tr>
-<tr><td class="l"> </td><td class="l">10 </td><td class="l">in octahedrons </td><td class="l"><a href="#species_Diamond">diamond</a></td></tr>
-<tr><td class="l"> </td><td class="l">9 </td><td class="l">in hexagonal prisms </td><td class="l"><a href="#species_Corundum">corundum</a></td></tr>
-<tr><td class="l"> </td><td class="l">8 </td><td class="l">in hexagonal prisms </td><td class="l"><a href="#species_Topaz">topaz</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">in three-sided prisms </td><td class="l"><a href="#species_Tourmaline">tourmaline</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">in hexagonal prisms </td><td class="l"><a href="#species_Quartz">quartz</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">non-crystalline </td><td class="l"><a href="#species_Chalcedony">chalcedony</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 or 4.5 </td><td class="l">cubes with beveled edges </td><td class="l"><a href="#species_Boracite">boracite</a></td></tr>
-<tr><td class="l"> </td><td class="l">6 </td><td class="l">non-crystalline, pearly luster </td><td class="l"><a href="#species_Opal">opal</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">rhombohedrons </td><td class="l"><a href="#species_Willemite">willemite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">trapezohedrons </td><td class="l"><a href="#species_Analcite">analcite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">tufts of needle-like crystals </td><td class="l"><a href="#species_Natrolite">natrolite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">sheaf-like bundles of crystals </td><td class="l"><a href="#species_Stilbite">stilbite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5 </td><td class="l">hexagonal prisms with basal cleavage </td><td class="l"><a href="#species_Apatite">apatite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5 </td><td class="l">effervesces in acid </td><td class="l"><a href="#species_Smithsonite">smithsonite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5 </td><td class="l">becomes jelly-like in acid </td><td class="l"><a href="#species_Calamine">calamine</a></td></tr>
-<tr><td class="l"> </td><td class="l">4.5 </td><td class="l">monoclinic prisms </td><td class="l"><a href="#species_Colemanite">colemanite</a></td></tr>
-<tr><td class="l"> </td><td class="l">4 </td><td class="l">in cubes </td><td class="l"><a href="#species_Fluorite">fluorite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5 </td><td class="l">effervesces in acid, but one cleavage </td><td class="l"><a href="#species_Aragonite">aragonite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5 </td><td class="l">effervesces in acid, heavy </td><td class="l"><a href="#species_Cerrusite">cerrusite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3 </td><td class="l">effervesces in acid, rhomboidal cleavage </td><td class="l"><a href="#species_Calcite">calcite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3 </td><td class="l">no effervescence, but soluble in nitric acid </td><td class="l"><a href="#species_Anglesite">anglesite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2.5 </td><td class="l">in cubes tastes of salt </td><td class="l"><a href="#species_Halite">halite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2 </td><td class="l">soluble in water, sweetish taste </td><td class="l"><a href="#species_Borax">borax</a></td></tr>
-<tr><td class="l"> </td><td class="l">2 </td><td class="l">1 perfect cleavage, and two imperfect cleaves at 66 with each other </td><td class="l"><a href="#species_Gypsum">gypsum</a></td></tr>
-<tr><td colspan="4" class="l">White or with faint tinges of color due to impurities, such as pink, bluish, etc.</td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">hexagonal prisms </td><td class="l"><a href="#species_Quartz">quartz</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">non-crystalline </td><td class="l"><a href="#species_Chalcedony">chalcedony</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 or 4.5 </td><td class="l">cubes with beveled edges </td><td class="l"><a href="#species_Boracite">boracite</a></td></tr>
-<tr><td class="l"> </td><td class="l">6 </td><td class="l">non-crystalline, pearly luster </td><td class="l"><a href="#species_Opal">opal</a></td></tr>
-<tr><td class="l"> </td><td class="l">6 </td><td class="l">cleavage in 3 directions, good in 2 and imperfect in the other </td><td class="l"><a href="#species_Feldspar">feldspar</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">short eight-sided prisms </td><td class="l"><a href="#species_Pyroxene">pyroxene</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">long six-sided prisms </td><td class="l"><a href="#species_Amphibole">amphibole</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">trapezohedrons </td><td class="l"><a href="#species_Analcite">analcite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">tufts of needle-like crystals </td><td class="l"><a href="#species_Natrolite">natrolite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">sheaf-like bundles of crystals </td><td class="l"><a href="#species_Stilbite">stilbite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">rhombohedrons </td><td class="l"><a href="#species_Willemite">willemite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5 </td><td class="l">effervesces in acid </td><td class="l"><a href="#species_Smithsonite">smithsonite</a></td></tr>
-<tr><td class="l"> </td><td class="l">5 </td><td class="l">becomes jelly-like in acid </td><td class="l"><a href="#species_Calamine">calamine</a></td></tr>
-<tr><td class="l"> </td><td class="l">4.5 &amp; 7 </td><td class="l">cubes with beveled edges </td><td class="l"><a href="#species_Boracite">boracite</a></td></tr>
-<tr><td class="l"> </td><td class="l">4.5 </td><td class="l">monoclinic prisms </td><td class="l"><a href="#species_Colemanite">colemanite</a></td></tr>
-<tr><td class="l"> </td><td class="l">4 </td><td class="l">effervesces in acid, porcelainous </td><td class="l"><a href="#species_Magnesite">magnesite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5-4 </td><td class="l">effervesces in acid, heavy, red color in flame </td><td class="l"><a href="#species_Strontianite">strontianite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5 </td><td class="l">effervesces in acid, heavy, green color in flame </td><td class="l"><a href="#species_Witherite">witherite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5 </td><td class="l">effervesces in warm acid, rhomboidal cleavage </td><td class="l"><a href="#species_Dolomite">dolomite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5 </td><td class="l">effervesces in acid, cleavage in one direction only </td><td class="l"><a href="#species_Aragonite">aragonite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5 </td><td class="l">effervesces in acid, heavy, does not color flame </td><td class="l"><a href="#species_Cerrusite">cerrusite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3-3.5 </td><td class="l">no effervescence, cleavage in three directions at right angles </td><td class="l"><a href="#species_Anhydrite">anhydrite</a></td></tr>
-<tr class="pbtr"><td colspan="5">
-</td></tr>
-<tr><td class="l"> </td><td class="l">3 </td><td class="l">effervesces in acid, rhomboidal cleavage </td><td class="l"><a href="#species_Calcite">calcite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3 </td><td class="l">tabular crystals, heavy, green color in flame </td><td class="l"><a href="#species_Barite">barite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2-3 </td><td class="l">cleaves in thin elastic sheets </td><td class="l"><a href="#species_Mica">mica</a></td></tr>
-<tr><td class="l"> </td><td class="l">2.5 </td><td class="l">cleaves in cubes </td><td class="l"><a href="#species_Cryolite">cryolite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2.5 </td><td class="l">cubes, soluble in water, salty taste </td><td class="l"><a href="#species_Halite">halite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2 </td><td class="l">1 perfect cleavage, and 2 less perfect ones </td><td class="l"><a href="#species_Gypsum">gypsum</a></td></tr>
-<tr><td class="l"> </td><td class="l">2 </td><td class="l">cleaves in thin non-elastic sheets </td><td class="l"><a href="#species_Chlorite">chlorite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2 </td><td class="l">soluble in water, tastes sweet </td><td class="l"><a href="#species_Borax">borax</a></td></tr>
-<tr><td class="l"> </td><td class="l">1 </td><td class="l">greasy feel </td><td class="l"><a href="#species_Talc">talc</a></td></tr>
-<tr><td class="l">Green </td><td class="l">9 </td><td class="l">hexagonal prisms </td><td class="l"><a href="#species_Corundum">oriental emerald</a></td></tr>
-<tr><td class="l"> </td><td class="l">8 </td><td class="l">octahedrons </td><td class="l"><a href="#species_Spinel">spinel</a></td></tr>
-<tr><td class="l"> </td><td class="l">7.5 </td><td class="l">hexagonal prisms </td><td class="l"><a href="#species_Beryl">beryl</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">three-sided prisms </td><td class="l"><a href="#species_Tourmaline">tourmaline</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">dodecahedrons or trapezohedrons </td><td class="l"><a href="#species_Garnet">garnet</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">non-crystalline </td><td class="l"><a href="#species_Prase">prase</a> or <a href="#species_Plasma">plasma</a></td></tr>
-<tr><td class="l"> </td><td class="l">6.5-7 </td><td class="l">non-crystalline, olive color </td><td class="l"><a href="#species_Olivine">olivine</a></td></tr>
-<tr><td class="l"> </td><td class="l">6.5 </td><td class="l">yellow green color, rather opaque </td><td class="l"><a href="#species_Epidote">epidote</a></td></tr>
-<tr><td class="l"> </td><td class="l">6 </td><td class="l">non-crystalline, pearly luster </td><td class="l"><a href="#species_Opal">opal</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">short eight-sided prisms </td><td class="l"><a href="#species_Pyroxene">pyroxene</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">long six-sided prisms </td><td class="l"><a href="#species_Amphibole">amphibole</a></td></tr>
-<tr><td class="l"> </td><td class="l">5 </td><td class="l">hexagonal prisms </td><td class="l"><a href="#species_Apatite">apatite</a></td></tr>
-<tr><td class="l"> </td><td class="l">4 </td><td class="l">cubes </td><td class="l"><a href="#species_Fluorite">fluorite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5 </td><td class="l">effervesces in acid </td><td class="l"><a href="#species_Cerrusite">cerrusite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2.5-4 </td><td class="l">somewhat greasy feel, massive or fibrous </td><td class="l"><a href="#species_Serpentine">serpentine</a></td></tr>
-<tr><td class="l"> </td><td class="l">2 </td><td class="l">in mica-like scales, non-elastic </td><td class="l"><a href="#species_Chlorite">chlorite</a></td></tr>
-<tr><td class="l"> </td><td class="l">1 </td><td class="l">greasy feel, fibrous or scaly </td><td class="l"><a href="#species_Talc">talc</a></td></tr>
-<tr><td class="l">Red </td><td class="l">9 </td><td class="l">hexagonal prisms </td><td class="l"><a href="#species_Corundum">ruby</a></td></tr>
-<tr><td class="l"> </td><td class="l">8 </td><td class="l">octahedrons </td><td class="l"><a href="#species_Spinel">spinel</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">three-sided prisms </td><td class="l"><a href="#species_Tourmaline">tourmaline</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">dodecahedrons or trapezohedrons </td><td class="l"><a href="#species_Garnet">garnet</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">hexagonal </td><td class="l"><a href="#species_RoseQuartz">rose quartz</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">non-crystalline </td><td class="l"><a href="#species_Jasper">jasper</a> or <a href="#species_Carnelian">carnelian</a></td></tr>
-<tr><td class="l"> </td><td class="l">6 </td><td class="l">pearly luster </td><td class="l"><a href="#species_FireOpal">fire opal</a></td></tr>
-<tr><td class="l"> </td><td class="l">4 </td><td class="l">cubes, rose tints </td><td class="l"><a href="#species_Fluorite">fluorite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2-3 </td><td class="l">pink mica-like scales </td><td class="l"><a href="#species_Mica">lepidolite</a></td></tr>
-<tr><td class="l">Blue </td><td class="l">9 </td><td class="l">hexagonal prisms </td><td class="l"><a href="#species_Corundum">sapphire</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 &amp; 4.5 </td><td class="l">blade-like crystals </td><td class="l"><a href="#species_Cyanite">cyanite</a></td></tr>
-<tr><td class="l"> </td><td class="l">6 </td><td class="l">non-crystalline masses </td><td class="l"><a href="#species_Turquois">turquois</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5-6 </td><td class="l">in igneous rocks </td><td class="l"><a href="#species_Sodalite">sodalite</a></td></tr>
-<tr><td class="l"> </td><td class="l">4 </td><td class="l">azure color </td><td class="l"><a href="#species_Azurite">azurite</a></td></tr>
-<tr><td class="l"> </td><td class="l">3.5 </td><td class="l">effervesces in acid, heavy </td><td class="l"><a href="#species_Cerrusite">cerrusite</a></td></tr>
-<tr><td class="l"> </td><td class="l">2-4 </td><td class="l">earthy masses, turquoise color </td><td class="l"><a href="#species_Chrysocolla">chrysocolla</a></td></tr>
-<tr><td class="l">Violet </td><td class="l">7 </td><td class="l">hexagonal prisms </td><td class="l"><a href="#species_Amethyst">amethyst</a></td></tr>
-<tr><td class="l"> </td><td class="l">4 </td><td class="l">cubes </td><td class="l"><a href="#species_Fluorite">fluorite</a></td></tr>
-<tr><td class="l">Yellow </td><td class="l">9 </td><td class="l">hexagonal prisms </td><td class="l"><a href="#species_Corundum">oriental topaz</a></td></tr>
-<tr><td class="l"> </td><td class="l">8 </td><td class="l">octahedrons </td><td class="l"><a href="#species_Spinel">spinel</a></td></tr>
-<tr><td class="l"> </td><td class="l">8 </td><td class="l">hexagonal prisms </td><td class="l"><a href="#species_Topaz">topaz</a></td></tr>
-<tr><td class="l"> </td><td class="l">4 </td><td class="l">cubes </td><td class="l"><a href="#species_Fluorite">fluorite</a></td></tr>
-<tr><td class="l">Brown </td><td class="l">9 </td><td class="l">hexagonal prisms </td><td class="l"><a href="#species_Corundum">corundum</a></td></tr>
-<tr><td class="l"> </td><td class="l">8 </td><td class="l">octahedrons </td><td class="l"><a href="#species_Spinel">spinel</a></td></tr>
-<tr><td class="l"> </td><td class="l">7.5 </td><td class="l">four-sided prisms </td><td class="l"><a href="#species_Zircon">zircon</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">hexagonal prisms </td><td class="l"><a href="#species_SmokyQuartz">smoky quartz</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">three-sided prisms </td><td class="l"><a href="#species_Tourmaline">tourmaline</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">non-crystalline </td><td class="l"><a href="#species_Flint">flint</a></td></tr>
-<tr><td class="l"> </td><td class="l">6 </td><td class="l">non-crystalline </td><td class="l"><a href="#species_Opal">opal</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">short eight-sided prisms </td><td class="l"><a href="#species_Pyroxene">pyroxene</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">long six-sided prisms </td><td class="l"><a href="#species_Amphibole">amphibole</a></td></tr>
-<tr><td class="l"> </td><td class="l">2-3 </td><td class="l">cleaves into thin sheets </td><td class="l"><a href="#species_Mica">mica</a></td></tr>
-<tr><td class="l">Black </td><td class="l">9 </td><td class="l">hexagonal prisms </td><td class="l"><a href="#species_Corundum">corundum</a></td></tr>
-<tr><td class="l"> </td><td class="l">8 </td><td class="l">octahedrons </td><td class="l"><a href="#species_Spinel">spinel</a></td></tr>
-<tr><td class="l"> </td><td class="l">7 </td><td class="l">three-sided prisms </td><td class="l"><a href="#species_Tourmaline">tourmaline</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">short eight-sided prisms </td><td class="l"><a href="#species_Pyroxene">pyroxene</a></td></tr>
-<tr><td class="l"> </td><td class="l">5.5 </td><td class="l">long six-sided prisms </td><td class="l"><a href="#species_Amphibole">amphibole</a></td></tr>
-<tr><td class="l"> </td><td class="l">2-3 </td><td class="l">cleaves in thin sheets </td><td class="l"><a href="#species_Mica">mica</a></td></tr>
-</table>
-<div class="pb" id="Page_29">29</div>
-<h3 class="center"><span class="sc">The Gold Group</span></h3>
-<p>Gold was undoubtedly the first metal to be
-used by primitive man; for, occurring as it did
-in the stream beds, its bright color quickly
-attracted the eye, and it was so soft, that it was
-easily worked into various shapes, which, because
-they did not tarnish, became permanent ornaments.
-The metal is associated with the very
-earliest civilizations, being found in such ancient
-tombs as those at Kertsch in Crimea and in
-northern Africa and Asia Minor. It was used
-in the cloisonn&eacute; work of Egypt 3000 years <span class="small">B.C.</span>
-In America the Indians, especially to the south,
-were using it long before the continent was
-discovered.</p>
-<p>Of all the metals gold is the most malleable,
-and its ductility is remarkable, for a piece of a
-grain&rsquo;s weight (less than the size of a pin head)
-can be drawn out into a wire 500 feet long; and
-<span class="pb" id="Page_30">30</span>
-it can be beaten into a thin leaf as thin as &sup1;/&#8322;&#8325;&#8320;&#8320;&#8320;&#8320;
-of an inch in thickness, and thus a bit, weighing
-only a grain, can thus be spread over 56 square
-inches.</p>
-<p>It forms very few compounds, but has a
-considerable tendency to make alloys (<i>i.e.</i>, mixtures
-with other metals without the resulting
-compound losing its metallic character). In
-Nature gold is never entirely pure, but is an
-alloy, usually with silver, there being from a
-fraction of 1% up to 30% of the silver with the
-gold, the more silver in the alloy, the paler the
-color of the gold. Australian gold is the purest,
-having but about .3% of silver in it, while
-Californian gold has around 10% and Hungarian
-gold runs as high as 30% of silver. Another
-alloy fairly abundant in Nature is that with
-tellurium, such as <i>calaverite</i> (AuTe&#8322;) which is a
-pale brassy yellow, similar to pyrite, but with the
-hardness of but 2.5. Another combination
-includes gold, silver and tellurium, <i>sylvanite</i>,
-(AuAgTe&#8324;) a silvery white mineral with a hardness
-of but 2. Such combinations are known
-as tellurides and the calaverite is mined as a source
-of gold at Cripple Creek, Colo., while the sylvanite
-is one of the important ores of gold in South
-Africa. Occasionally gold is also found alloyed
-with platinum, copper, iron, etc. Jewelers make
-several alloys, &ldquo;red gold&rdquo; being 3 parts gold and
-1 of copper, &ldquo;green gold&rdquo; being the same proportions
-of gold and silver, and &ldquo;blue gold&rdquo;
-being the combination of gold and iron. Our
-gold coins are alloys, nine parts gold and one of
-copper, to give them greater durability. Most of
-<span class="pb" id="Page_31">31</span>
-the gold recovered from nature is found native,
-<i>i.e.</i>, the pure metal, or with some alloy.</p>
-<h3><a id="species_Gold">Gold</a>
-<br />Au
-<br /><a href="#Plate_5">Pl. 5</a></h3>
-<p>Usually non-crystalline, but occasionally
-showing cube or octahedral
-faces of the isometric system; hardness
-2.5; specific gravity 19.3; color golden yellow;
-luster metallic; opaque.</p>
-<p>Gold is mostly found as the metal and is
-readily recognized by its color, considerable
-weight, hardness, malleability, and the fact that
-it does not tarnish. It usually occurs in quartz
-veins in fine to thick threads, scales or grains,
-and occasionally in larger masses termed &ldquo;nuggets.&rdquo;
-It is insoluble in most liquids so that
-when weathered from its original sites, it was
-often washed down into stream beds, to be found
-later in the sands or gravels, or even in the sea
-beaches. When thus found it is termed &ldquo;placer
-gold,&rdquo; and its recovery is placer mining. Most
-of the original discoveries of gold have been in
-these placer deposits; and from them it has
-been traced back to the ledges from which it
-originally weathered. In the placer deposits the
-size of the particles varies from fine &ldquo;dust&rdquo;
-up to large nuggets, the largest found in California
-weighing 161 pounds; but the largest one
-found in the world was the &ldquo;Welcome Nugget,&rdquo;
-found in Australia, and weighing 248 pounds.
-When gold was discovered in California in 1848,
-this became the chief source for the world, but
-later this distinction went to Australia, and now
-belongs to South Africa, which today yields over
-half the annual supply.</p>
-<div class="pb" id="Page_32">32</div>
-<p>The ultimate source of gold is from the lighter
-colored igneous rocks, like granites, syenites,
-and diorites, throughout which it is diffused in
-quantities too small to be either visible or worth
-while to extract. It becomes available only
-when it has been dissolved out by percolating
-waters and segregated in fissures or veins, either
-in or leading from these igneous rocks. Generally
-this transfer of gold has taken place when
-the rocks were at high temperatures, and by the
-aid of water (and perhaps other solvents) which
-was also at high temperatures. The presence
-of gold in sandstones, limestones, etc., is secondary,
-as is also its presence in sea water, in which
-there is reported to be nearly a grain (about five
-cents worth) in every ton of water. Beside the
-direct recovery of gold from gold mining, a great
-deal is obtained from its association with iron,
-copper, silver, lead and zinc sulphides, in which
-it is included in particles too fine to be visible,
-but in quantities large enough to be separated
-from the other metals after they are smelted.</p>
-<p>In the United States gold is found in the
-Cordilleran region from California to Alaska, in
-Colorado, Nevada, Arizona, Utah, the Black
-Hills of South Dakota, and in small quantities
-in the metamorphosed slates of North and South
-Carolina, Georgia, and in Nova Scotia.</p>
-<h3 class="center"><span class="sc">The Silver Group</span></h3>
-<p>Though much commoner than gold, silver did
-not attract the eye of man as early, probably
-because it tarnishes when exposed to air or any
-other agent having sulphur compounds in it,
-<span class="pb" id="Page_33">33</span>
-and a black film of silver sulphide covers the
-surface. Its first use was for ornaments, and
-some of these found in the ruins of ancient Troy
-indicate its use as early as 2500 <span class="small">B.C.</span> A thousand
-years later it was being used to make basins,
-vases and other vessels.</p>
-<p>Silver is next to gold in malleability and
-ductility, so that a grain of silver can be drawn
-out into a wire 400 feet long, or beaten into
-leaves &sup1;/&#8321;&#8320;&#8320;&#8320;&#8320;&#8320; of an inch in thickness. As a
-conductor of electricity it is unsurpassed, being
-rated at 100% while copper rates 93%. Silver
-is also like gold in the freedom with which it
-alloys with other metals, such as gold, copper,
-iron, platinum, etc. All our silver coins, tableware,
-etc., have some copper alloyed with the
-silver to give it greater hardness and durability.</p>
-<p>Unlike gold, silver freely enters into compounds
-with the non-metals, which is the reason
-that it is not found primarily in its native state,
-but usually as a sulphide. Its ultimate source
-is in the igneous rocks, few granites or lavas, on
-analysis, failing to show at least traces of silver.
-Before it is available as an ore, or mineral, it has
-been dissolved from the original magma, and
-segregated in fissures or veins, along with such
-minerals, as quartz, fluorite, calcite, etc. This
-seems to have taken place while the igneous
-rocks were still hot, and by the agency of vapors
-and liquids which were also hot. The presence
-of silver in sedimentary and metamorphic rocks,
-or even in sea water, is secondary.</p>
-<p>The primary deposition of silver is usually in
-the form of sulphides, the commoner of which
-<span class="pb" id="Page_34">34</span>
-are, argentite or silver sulphide, pyrargyrite
-or silver and antimony sulphide, and prousite, or
-silver and arsenic sulphide. Its occurrence as
-native silver, or the chloride, cerargyrite, is
-secondary and due to the reactions which have
-taken place when sulphide deposits have been
-subjected to weathering agents.</p>
-<p>The United States produces about 25% of the
-world&rsquo;s supply, Mexico some 35%. It is especially
-found along the Cordilleran ranges of both
-North and South America.</p>
-<h3><a id="species_Silver">Silver</a>
-<br />Ag
-<br /><a href="#Plate_6">Pl. 6</a></h3>
-<p>Usually non-crystalline, but
-occasionally showing cube or octahedron
-faces of the isometric system;
-hardness 2.5; specific gravity 10.5; color silvery
-white; luster metallic; opaque.</p>
-<p>When found in its native state silver is usually
-in wirey, flakey, or mossy masses; but sometimes
-masses of considerable size occur, the most
-famous being an 800 pound nugget found in Peru,
-and another of 500 pounds weight found at
-Konsberg, Norway, and now preserved in Copenhagen.
-When exposed to the air the surface
-soon tarnishes and takes on a black color which
-must be scraped off to see the real color.</p>
-<p>Like gold, silver is usually found associated
-with other metals, like iron, copper, lead and
-zinc; and much of the silver recovered is obtained
-in connection with the mining, especially
-of copper and lead. Some lead ores have so
-much silver in them that they are better worth
-mining for the silver; galena, for instance, under
-such circumstances being termed argentiferous
-<span class="pb" id="Page_35">35</span>
-galena. Native silver is a secondary mineral,
-having been formed by the reduction of some one
-of its sulphides by water, carrying various elements
-which had a greater affinity for the sulphur.</p>
-<p>Silver is found along with copper in the Lake
-Superior region, and in Idaho, Nevada, and
-California.</p>
-<h3><a id="species_Argentite">Argentite</a>
-<br />AgS
-<br /><a href="#Plate_6">Pl. 6</a>
-<br /><i>silver glance</i></h3>
-<p>Usually in irregular masses, but
-sometimes in cubes; hardness 2.5;
-specific gravity 7.3; color and streak
-lead gray; luster metallic; opaque on thin edges.</p>
-<p>Argentite, the simple sulphide of silver, is the
-chief source from which silver is obtained. It
-looks like galena, and has the same hardness,
-streak and specific gravity, but can be distinguished
-by the galena having a very perfect
-cubic cleavage while the argentite has no cleavage.
-Argentite is easily cut with a knife (sectile).
-It is usually found in irregular masses, but sometimes
-in cubes which make very choice cabinet
-specimens; and is associated with such other
-minerals as galena, sphalerite, chalcopyrite,
-pyrite, fluorite, quartz, and calcite.</p>
-<p>It occurs in fissures and veins all through the
-Cordilleran regions, especially in California,
-Colorado, Nevada (Comstock Lode), Arizona
-(Silver King Mine) and about the shores of
-Lake Superior.</p>
-<h3><a id="species_Pyrargyrite">Pyrargyrite</a>
-<br />Ag&#8323;SbS&#8323;
-<br /><a href="#Plate_7">Pl. 7</a>
-<br /><i>ruby silver</i> or <i>dark red silver</i></h3>
-<p>Usually occurs in irregular masses;
-hardness 2.5; specific gravity 5.8;
-color dark red to black; streak purplish
-red; luster metallic to adamantine;
-translucent on thin edges.</p>
-<div class="pb" id="Page_36">36</div>
-<p>Pyrargyrite, the sulphide of silver and antimony,
-is distinguished by its dark red color and
-the purplish streak. It may look like prousite,
-but is easily distinguished from the latter which
-has a scarlet streak. It also at times looks like
-hematite and cinnabar, but the hematite has a
-hardness of 6, and the latter has the bright red
-color throughout, while pyrargyrite turns black
-when exposed to the light, so that the characteristic
-red color will be seen only on fresh
-surfaces. The characteristic red color can only
-be kept on the mineral if it is constantly protected
-from the light.</p>
-<p>Sometimes pyrargyrite occurs in crystals and
-these belong to the hexagonal system, and are
-prisms with low faces on the ends, as on <a href="#Plate_7">plate 7</a>,
-and the mineral is peculiar in that the faces on
-the opposite ends are unlike.</p>
-<p>Pyrargyrite is found mostly in fissures and
-veins of quartz, fluorite, calcite, etc., and associated
-with pyrite, chalcopyrite, galena, etc.
-It is fairly common in Colorado in Gunnison
-and Ouray counties, in Nevada, New Mexico,
-Arizona, etc.</p>
-<h3><a id="species_Prousite">Prousite</a>
-<br />Ag&#8323; AsS&#8323;
-<br /><a href="#Plate_7">Pl. 7</a>
-<br /><i>light red</i>
-<br /><i>silver</i></h3>
-<p>Usually occurs in irregular masses;
-hardness 2.5; specific gravity 5.6;
-color scarlet to vermilion; streak
-the same; luster adamantine; transparent
-on thin edges.</p>
-<p>In general this mineral is very like pyrargyrite,
-but has the scarlet color and streak which are
-entirely characteristic. It is likely to have the
-surface tarnished black, which happens on exposure
-<span class="pb" id="Page_37">37</span>
-to light, so that it is essential to be sure
-that fresh surfaces are being examined. Occasionally
-it is found in crystals, of the same
-type as the preceding mineral. It is generally
-found associated with pyrargyrite.</p>
-<h3><a id="species_Cerargyrite">Cerargyrite</a>
-<br />AgCl
-<br /><i>horn silver</i></h3>
-<p>Usually found in irregular masses
-or incrustations; hardness 1 to 1&frac12;;
-specific gravity 5.5; color pearly gray,
-grayish green to colorless, but turning violet
-brown on exposure to light; luster resinous;
-transparent on thin edges.</p>
-<p>This mineral is usually found in thin seams
-or waxy incrustations, but it may occur in crystals
-in which case they are cubes. It is very
-soft and easily cut with a knife, which with its
-tendency to turn violet-brown on exposure to
-light, makes it easy to identify. Cerargyrite is a
-secondary mineral, resulting from the action of
-chlorine-bearing water on some one of the
-sulphides of silver. It is found in the upper
-portions of mines, especially those in arid regions.</p>
-<h3 class="center"><span class="sc">The Copper Group</span></h3>
-<p>After gold the next metal to be utilized was
-copper. About 4000 <span class="small">B.C.</span> our early forefathers
-found that by heating certain rocks, they obtained
-a metal which could be pounded, ground
-and carved into useful shapes. Curiously enough
-the rocks which had the copper also had some
-tin in them, so that this first-found copper was
-not pure, but had from five to ten per cent of tin
-in it, making the resulting metal harder, and
-<span class="pb" id="Page_38">38</span>
-what we call bronze. It was some thousands of
-years later before they distinguished the copper
-as a pure metal, but it worked and made good
-tools. The newly found metal was not as ornamental
-as gold; but, because it could be made
-into tools, it had a tremendous influence on
-man&rsquo;s development. As the bronze tools began
-to take the place of the stone implements, the
-&ldquo;Age of Bronze&rdquo; was ushered in. In America
-the Indians in the Lake Superior region found
-native copper weathered out of the rocks and
-later mined it, and they too pounded it into
-knives, axes, needles, and ornaments, but probably
-never learned to melt it and mold their
-tools. At any rate they were not as far advanced
-in using this metal when Columbus
-landed as were the southern Europeans 6500
-years earlier. Since the use of iron became
-general, copper has not held such a dominant
-place, but it still is &ldquo;the red metal&rdquo; which holds
-the second most important place.</p>
-<p>It is malleable and ductile, though not equal
-to gold or silver in these respects. It is a good
-conductor of electricity and a very large amount
-of copper is used in electrical manufacture,
-roofing, wire, etc. It alloys with other metals;
-ten parts copper and one of tin being bronze, ten
-of copper and one of zinc is brass, and copper
-with aluminum is aluminum bronze.</p>
-<p>Like silver and gold, copper is widely diffused
-through the igneous rocks, but before it is available,
-it must be leached out by solvents and concentrated
-in veins, fissures, or definite parts of
-the lavas or granites. The primary ores are
-<span class="pb" id="Page_39">39</span>
-those which, while the igneous rock was still
-hot, were carried by hot vapors and liquids into
-the fissures and there deposited, mostly as sulphides.
-There is a long list of these, but in this
-country, the following are the commoner ones;
-chalcocite the sulphide of copper, chalcopyrite
-the sulphide of copper and iron, bornite another
-combination of copper, iron and sulphur, and
-tetrahedrite copper and antimony sulphide.
-When these primary ores are near enough to the
-surface to come in contact with waters carrying
-oxygen, carbon dioxide or silica in solution, they
-may give up their sulphur and take some one of
-these new elements and we have such forms as
-cuprite, the oxide of copper, malachite and
-azurite, carbonates of copper, or chrysocolla,
-the silicate of copper. Native copper is also a
-secondary deposit laid down in its present state
-by a combination of circumstances which deprived
-it of its original sulphur. In general
-copper mining can not be profitably carried on
-for ores with anything less than a half of one
-percent in them; and the use of such low grade
-ores has only been possible for a few years, as
-the result of inventing most delicate processes
-in the smelting.</p>
-<p>The United States produces about a quarter of
-the world&rsquo;s supply of copper, with Chile ranking
-second with about 17%.</p>
-<h3><a id="species_Copper">Copper</a>
-<br />Cu
-<br /><a href="#Plate_8">Pl. 8</a></h3>
-<p>Usually in irregular masses; hardness
-2.5; specific gravity 8.9; color
-copper red; luster metallic; opaque.
-Native copper, easily determined by its color
-<span class="pb" id="Page_40">40</span>
-and hardness, is generally found in irregular
-grains, sheets, or masses, on which may sometimes
-be detected traces of a cube or an octahedral
-face, showing that it belongs to the
-isometric system. The most famous locality is
-the Upper Peninsula of Michigan which may be
-taken as typical. Here, long before it was known
-historically, the Indians found and dug out copper
-to make knives, awls, and ornaments.</p>
-<p>In this region, beds of lava alternate with
-sandstones and conglomerates. The copper was
-originally in the lavas, but has been dissolved
-out, and now fills cracks and gas cavities in the
-lavas, and also the spaces between the pebbles
-of the conglomerate. This locality has been
-very famous both because of the quantity mined,
-and also because of the strikingly large masses
-sometimes found. Today but little of the ore
-runs above 2 percent copper, and it is mined
-if it has as little as &frac12; of one percent.</p>
-<p>While nowhere near as abundant, native
-copper occurs in the same way in cavities and
-cracks in the trap rocks of New Jersey, and along
-the south shore of the Bay of Fundy. It is also
-known from Oregon, the White River region of
-Alaska, and in Arctic Canada.</p>
-<h3><a id="species_Chalcopyrite">Chalcopyrite</a>
-<br />CuFeS&#8322;
-<br /><a href="#Plate_8">Pl. 8</a>
-<br /><i>copper pyrites</i> or <i>yellow copper ore</i></h3>
-<p>Occurs in crystals of irregular
-masses; hardness 4; specific gravity
-4.2; color bronze yellow; streak
-greenish black; luster metallic;
-opaque on thin edges.</p>
-<p>Chalcopyrite resembles pyrite, but
-its color is a more golden yellow, and its surface
-<span class="pb" id="Page_41">41</span>
-tarnishes with iridescent colors. Then too the
-hardness of chalcopyrite is but 4 as compared
-with 6 for pyrite. When in crystals this mineral
-belongs to the tetrahedral system as the c axis
-is but .985 in length as compared with I for the
-two other axes. This difference is so little that,
-to the eye, the octahedron appears to belong to
-the isometric system. Chalcopyrite occurs in
-octahedrons and tetrahedrons (as on <a href="#Plate_8">plate 8</a>),
-the latter being the form where but half of
-the octahedral faces are developed. However
-by far the most frequent mode of occurrence
-is in irregular masses.</p>
-<p>This is the most important primary ore of
-copper, and is widely distributed, being found
-either in lavas, or in veins, or in fissures connected
-with igneous rocks. Apparently the
-deposits were made, either at the time of eruptive
-disturbances or shortly afterward, from
-vapors or hot solutions carrying the copper
-sulphides (and other sulphides) from the molten
-igneous rocks. Chalcopyrite is usually associated
-with pyrite, galena, sphalerite and chalcocite, as
-well as quartz, fluorite and calcite. It is found in
-all the New England States, in New York, New
-Jersey, Pennsylvania, Maryland, Virginia, North
-Carolina, Tennessee, Missouri, and all the Rocky
-Mountain and Pacific Coast States.</p>
-<h3><a id="species_Bornite">Bornite</a>
-<br />Cu&#8323;FeS&#8323;
-<br /><i>purple copper ore</i></h3>
-<p>Occurs in granular or compact
-masses; hardness 3; specific gravity,
-5; color bronze-brown with a bluish
-tarnish; streak gray-black; luster
-metallic; opaque on thin edges.</p>
-<div class="pb" id="Page_42">42</div>
-<p>Bornite is also known as erubescite, blushing
-ore, variegated copper, peacock copper, etc.,
-all of which names refer to the highly iridescent
-tarnish which fresh faces soon take on when
-exposed to the air. Though usually in masses,
-it is sometimes found in rough cubes of the isometric
-system. In this country it is not abundant
-enough to be used as an ore, but is likely to be
-found with other ores like chalcopyrite or chalcocite.
-In the east it has been found at Bristol,
-Conn., and near Wilkesbarre, Penn., while in
-the west it may be expected to occur wherever
-other sulphide minerals of copper are found.</p>
-<h3><a id="species_Chalcocite">Chalcocite</a>
-<br />Cu&#8322;S
-<br /><a href="#Plate_9">Pl. 9</a>
-<br /><i>copper glance</i></h3>
-<p>Occurs in fine grained compact
-masses; hardness 2.5; specific gravity
-5.7; color dark leaden gray;
-streak black; luster metallic; opaque
-on thin edges.</p>
-<p>Chalcocite is one of the important ores of
-copper, especially in Arizona and the Butte
-District of Montana. It resembles argentite
-in color and general appearance, but is readily
-distinguished by being brittle and having a
-tendency to tarnish to bluish or greenish colors
-on fresh surfaces. Occasionally it occurs in
-crystals which are in the orthorhombic system;
-but the edges of the prism are so beveled that
-there are six sides and the prism resembles a
-hexagonal prism (see <a href="#Page_16">page 16</a>).</p>
-<p>In the Butte, Mont., district, the most important
-copper region in the United States, fully 50%
-of the ore is chalcocite, which is a derivative of
-the originally deposited chalcopyrite, the latter
-<span class="pb" id="Page_43">43</span>
-having lost its iron. In the veins of this district
-chalcopyrite, bournite, tetrahedrite, and several
-other copper minerals not described in this book,
-occur all together, and with them also gold,
-silver and arsenic minerals. The gold amounts
-to about 2&frac14; cents per pound of copper, and the
-silver is in somewhat less quantity. These veins
-were first opened to get the silver ores, which
-were the more important ones down to a depth
-of 200 to 400 feet. Below these depths the
-copper became much more important. It was
-the weathering which had removed a large part
-of the copper minerals in the upper levels of the
-veins, but had left a large part of the silver.
-Chalcocite is also important in most of the Utah
-and Arizona mines.</p>
-<p>In the east it has been found at Bristol, Simsbury
-and Cheshire, Conn., and in the west it is
-found in all the Cordilleran States.</p>
-<h3><a id="species_Tetrahedrite">Tetrahedrite</a>
-<br />Cu&#8323;SbS&#8323;
-<br />Pl. <a href="#Plate_9">9</a> &amp; <a href="#Plate_10">10</a>
-<br /><i>gray copper ore</i></h3>
-<p>Occurs in irregular masses and in
-tetrahedrons of the isometric system;
-hardness 3.5; specific gravity 4.7;
-streak dark brown; luster metallic;
-opaque on thin edges.</p>
-<p>In its crystalline form the tetrahedrite occurs
-in tetrahedrons, which generally have faces
-formed by beveling the edges and by cutting the
-corners, as in the two figures of <a href="#Plate_10">plate 10</a>. Chalcopyrite
-may also occur in tetrahedrons, but
-its golden yellow color is entirely different from
-the gray-black of the tetrahedrite. When in
-masses the hardness and the streak which is dark
-brown, are very characteristic.</p>
-<div class="pb" id="Page_44">44</div>
-<p>In England and Bolivia tetrahedrite is an
-important ore of copper, but in this country it is
-simply a copper mineral which is widely distributed,
-and associated with most of the mining
-enterprises, but is in no case the important ore.
-It has been found sparingly through the New
-England States, at the Kellogg Mines in
-Arkansas, and abundantly in Colorado, Montana,
-Utah, Arizona, Nevada and New Mexico.</p>
-<h3><a id="species_Cuprite">Cuprite</a>
-<br />Cu&#8322;O
-<br />Pl. <a href="#Plate_9">9</a> &amp; <a href="#Plate_10">10</a>
-<br /><i>red copper ore</i></h3>
-<p>Occurs in isometric cubes, octahedrons,
-and dodecahedrons, or in
-masses; hardness 3.5; specific gravity
-6; color dark brownish-red;
-streak brownish-red; luster metallic; translucent
-on thin edges.</p>
-<p>When in crystals cuprite is easily determined,
-but when in masses its fresh surfaces may suggest
-prousite, but the streak and hardness are
-quite different in the two cases. Sometimes its
-color suggests hematite, but the latter has the
-hardness of 6. When found it is often coated
-with a thin film of green, which is malachite.</p>
-<p>Except when found as native copper, the ore
-which contains the greatest percentage of copper
-is cuprite with 88.8% of copper. It is likely to
-occur in any of the deposits of copper ore, where
-they are in arid climates and above the level of
-the underground water, and is very frequently
-associated with malachite and azurite. In the
-Bisbee, Arizona, district cuprite is one of the
-important ores.</p>
-<p>Besides the normal occurrence described
-above, cuprite may be found in two other varieties;
-<span class="pb" id="Page_45">45</span>
-one where the crystals have grown side by
-side and so only the ends have been free for
-continuous additions of the mineral, which has
-resulted in a fibrous mass known as &ldquo;plush
-copper ore&rdquo; or chalcotrichite; the other an
-earthy mixture of limonite and cuprite, which is
-brick red in color, and termed &ldquo;tile ore.&rdquo;</p>
-<p>Cuprite is found sparingly in New England,
-more abundantly at such places as Summerville
-and Flemington, N. J., Cornwall, Penn., in the
-Lake Superior region, and fairly abundantly in
-the Cordilleran States.</p>
-<h3><a id="species_Malachite">Malachite</a>
-<br />CuCO&#8323;&middot;Cu(OH)&#8322;
-<br /><a href="#Plate_11">Pl. 11</a></h3>
-<p>Usually occurs in nodular or incrusting
-masses; hardness 3.5;
-specific gravity 4; color green; streak
-a lighter green; luster adamantine, silky or dull;
-translucent on thin edges.</p>
-<p>The vivid green of malachite is usually enough
-to determine it at once, but one may be sure
-by trying a drop of acid on it, in which case it
-effervesces as is characteristic of so many carbonates,
-but this is the only carbonate which is
-vivid green. Generally the malachite is in
-irregular masses, but crystals are occasionally
-found. These are extremely small and needle-like,
-and belong to the monoclinic system. In
-the Ural Mountains there is a locality where
-these crystals grow in fibrous masses, usually
-radiating from the center. Malachite in such
-nodules has a silky luster. These rare nodules
-have furnished the rulers of Russia with a unique
-and much prized material for making royal gifts.
-In European museums and palaces one finds
-<span class="pb" id="Page_46">46</span>
-many objects carved from this form of malachite,
-and marked as gifts of the czars of Russia.</p>
-<p>In the United States malachite is widely
-distributed, appearing as green streaks and
-stains where copper minerals have been exposed
-to the air. It is the green tarnish which appears
-on bronze and copper when exposed to the
-weather. It is found in large quantities in New
-Jersey, Pennsylvania, Wisconsin, Nevada, Arizona,
-Utah, New Mexico, etc. The Bisbee mine
-in Arizona is the place that has furnished museums
-with so many of the handsome specimens
-of malachite associated with azurite. These are
-the most striking specimens for the vividness of
-their colors that appear in any collections.</p>
-<p>Malachite has been known since about 4000
-<span class="small">B.C.</span>, the Egyptians having mines where they
-obtained it between the Suez and Mt. Sinai.
-In those early days it was particularly a child&rsquo;s
-charm, protecting the wearer from evil spirits.
-It is still used as a stone of lesser value in
-making some sorts of jewelry.</p>
-<h3><a id="species_Azurite">Azurite</a>
-<br />2CuCO&#8323;&middot;Cu(OH)&#8322;
-<br /><a href="#Plate_11">Pl. 11</a></h3>
-<p>Occurs as short prismatic or tabular
-crystals of the monoclinic system;
-hardness 4; specific gravity 3.8;
-color azure blue; streak lighter blue; luster
-vitreous; translucent on thin edges.</p>
-<p>Azurite is another very striking mineral fully
-characterized by its color and streak. Like
-malachite it effervesces in acid. It is very near
-to malachite in composition, and by increasing
-its water content, can and freely does change to
-the green mineral; so that few specimens of
-<span class="pb" id="Page_47">47</span>
-azurite are without traces of malachite. It is
-found in the same places as malachite, but is
-not as abundant in the east.</p>
-<p>Azurite with the accompanying malachite is
-cut and polished to make semi-precious stones
-for some forms of jewelry.</p>
-<h3><a id="species_Chrysocolla">Chrysocolla</a>
-<br />CuSiO&#8323;&middot;2H&#8322;O</h3>
-<p>Never occurs in crystals, but in
-seams and incrustations; hardness
-2-4; specific gravity 2.1; color bluish-green; streak
-white; luster vitreous; translucent on thin edges.</p>
-<p>This rather rare mineral often appears in opal-
-or enamel-like incrustations, and its color is
-variable ranging from the typical bluish-green to
-sky-blue or even turquoise blue. This is a
-mineral resulting from the action of silica bearing
-waters, coming in contact with most any of
-the copper minerals, and is found accompanying
-cuprite, malachite, azurite, etc. It is never in
-large enough quantities to be used as an ore, but
-its striking color attracts attention and it can be
-found fairly frequently, especially in the west.</p>
-<h3 class="center"><span class="sc">The Iron Group</span></h3>
-<p>Pure iron is a chemical curiosity which looks
-very much like silver. As obtained from its ores,
-or as it occurs in Nature, iron always has some
-impurities with it, such as carbon, silicon, sulphur
-and phosphorus, and these are highest in the
-crudest iron such as &ldquo;pig-iron.&rdquo; Its malleability
-and ductility are only a little less than for gold
-and silver, and so it has a wide range of qualities
-for use by man. It is only rarely found native in
-minute grains in some of the dark lavas. There
-<span class="pb" id="Page_48">48</span>
-is however one remarkable exception to this
-statement, in that on Disco Island, Greenland,
-there is a basaltic rock, from which are weathered
-great boulders of native iron up to 20 tons in
-weight. This iron is very like that occurring in
-meteorites, and probably came from great depths
-in the earth&rsquo;s interior. The specific gravity of
-iron is 7.8. It makes up around 5% of the crust
-of the earth, and probably occurs in much larger
-percentages in the interior of the earth.</p>
-<p>Iron was discovered by man later than gold or
-silver or copper, about 1000 <span class="small">B.C.</span>; but once found
-it was so much more abundant than any of
-these that it soon dominated over copper, and
-from Roman times to the present has been the
-basis of progress in civilization, and these times
-are well called &ldquo;the iron age.&rdquo;</p>
-<p>Iron unites freely with the non-metals, and
-occurs as sulphides, oxides, carbonates, etc., and
-is also present as a secondary metal in that
-great group of minerals known as the silicates
-(see <a href="#Page_97">page 97</a>). It alloys with a wide range of
-other metals, every combination altering the
-properties of the iron, and thus making it useful
-in a still greater range of manufacture. The
-introduction of &frac14; to 2&frac12;% of carbon into iron
-makes steel, which is harder (in proportion to the
-amount of carbon) and stronger than the pure iron.</p>
-<p>Iron compounds are among the most numerous
-and important of the colors in Nature&rsquo;s paint
-box, limonite furnishing the browns which color
-the soil and so many of the rocks, hematite giving
-the red color to other abundant rocks, and
-magnetite often coloring igneous rocks black,
-<span class="pb" id="Page_49">49</span>
-while the chlorophyll which gives the green
-color to plants is an iron compound, as is also the
-hemoglobin which gives the red to our blood.</p>
-<p>Iron is present in all igneous rocks, and
-secondarily in the sedimentary and metamorphic
-rocks. It is soluble in water, and so is being
-constantly transferred from place to place, and
-changes from one compound to another, according
-to the circumstances in which it is placed.</p>
-<p>The primary forms are pyrite, magnetite and
-the silicates. When in weathered rocks the iron
-is changed to limonite, siderite or hydrated silicates.
-Hematite is an intermediate oxide from
-which the water contained in limonite has been
-driven off by moderate heat or bacterial action.</p>
-<h3><a id="species_Limonite">Limonite</a>
-<br />2Fe&#8322;O&#8323;&middot;3H&#8322;O
-<br /><a href="#Plate_12">Pl. 12</a></h3>
-<p>Never crystalline, occurs in mammillary,
-botryoidal and stalactitic
-forms, or in fibrous, compact, oolitic,
-nodular or earthly masses; hardness 5.5; specific
-gravity 3.8; color yellow-brown to black; streak
-yellow-brown; luster metallic to dull; opaque.</p>
-<p>Limonite is a very common mineral, the color,
-streak and hardness identifying it readily. Iron
-rust is its most familiar form. When powdered
-it is the ochre yellow used in paints. Being so
-universally distributed, it is to be expected it will
-occur in a variety of ways. First, there is the
-fibrous type found lining cavities, in geodes, or
-hanging in stalactites in caves. This has a
-silky luster, an opalescent, glazed or black surface,
-and is in mammillated or botryoidal masses.
-Second, it may occur in compact masses in veins,
-where it was deposited by waters; which, circulating
-<span class="pb" id="Page_50">50</span>
-through the adjacent rocks, gathered it
-from the rocks, and, on reaching the open seams,
-gave it up again. Third, it may occur in beds
-on the bottom of ponds, where it was deposited
-by waters which gathered it as they flowed over
-the surface of the country rocks. Measurements
-in Sweden show that it may accumulate in such
-places as much as six inches in the course of
-twenty years. In ponds and swamps, the decaying
-vegetation forms organic compounds, which
-cause the precipitation of the iron from the water,
-as it is brought in by the streams. This sort of
-iron in the bottom of ponds or swamps is also
-known as &ldquo;bog iron.&rdquo; Another form in which
-limonite may occur in ponds, lakes, or even the
-sea, is in oolitic masses. In this case the iron
-forms in tiny balls, with perhaps a grain of sand
-at the center, and one coat of iron after another
-formed around it, like the layers of an onion. If
-the resulting balls are tiny this is called oolitic
-(like fish eggs), but if the balls are larger it is
-pisolitic (like peas). Bacteria probably have a
-good deal to do with the precipitation of limonite
-in this manner. Fourth, limonite occurs in
-earthy masses, usually mixed with impurities
-like clay and sand, which are the residue left
-behind, where limestones have been dissolved by
-weathering. The fifth mode of occurrence is
-known as gossan, or &ldquo;the iron hat,&rdquo; which is a
-mass of limonite capping a vein of some sulphide
-mineral, like pyrite, chalcopyrite or pyrrhotite,
-which has been exposed to weathering; and in
-these minerals the sulphur has been removed,
-leaving a mass of limonite over the vein. This is
-<span class="pb" id="Page_51">51</span>
-particularly common in the west. Limonite is
-quite easily fusible and so was probably the
-first ore from which early man extracted iron.</p>
-<p>Limonite is iron oxide, with 3 molecules of
-water of crystallization (or constitution) associated
-with every 2 molecules of the oxide. If
-limonite is moderately heated the water is
-driven out and the resulting compound is hematite,
-the same oxide, but without the water. In
-this case and many other similar cases, as
-gypsum, opal, etc., we have two or more minerals
-resulting from the presence or absence of water
-in the mineral. The water molecules have a
-definite place in the arrangement of molecules
-which determines the structure of the mineral.
-Sometimes the water is driven out at a temperature
-around 212 F., in which case it is called,
-water of crystallization, but in other cases as
-gypsum, a considerably higher temperature is
-required to drive out the water, and then it is
-called, water of constitution. In all cases the
-removal of the water changes the arrangement of
-molecules and a new mineral results, with
-characteristics of its own.</p>
-<p>In this case limonite is only one of a series of
-minerals which have the Fe&#8322;O&#8323; molecule as a
-basis, and that incorporate more or less water
-into their molecular construction as follows:</p>
-<table class="center" summary="">
-<tr><td class="lbottom">Turgite </td><td class="lbottom">2Fe&#8322;O&#8323;&middot;H&#8322;O</td></tr>
-<tr><td class="lbottom">Goethite </td><td class="lbottom">Fe&#8322;O&#8323;&middot;H&#8322;O</td></tr>
-<tr><td class="lbottom">Limonite </td><td class="lbottom">2Fe&#8322;O&#8323;&middot;3H&#8322;O</td></tr>
-<tr><td class="lbottom">Xanthosiderite </td><td class="lbottom">Fe&#8322;O&#8323;&middot;2H&#8322;O</td></tr>
-<tr><td class="lbottom">Limonite </td><td class="lbottom">Fe&#8322;O&#8323;&middot;3H&#8322;O</td></tr>
-</table>
-<div class="pb" id="Page_52">52</div>
-<p>Of these goethite is crystalline, the others non-crystalline.
-They may occur pure or in all
-sorts of mixtures, the mixtures usually being
-lumped under limonite. The limonite is far
-the commonest of the series, goethite is fairly
-common, but the others are rare as pure
-minerals.</p>
-<p>Limonite is found in all parts of all states and
-in every country. Though so common, it is by
-no means an important source of iron today,
-only about one percent of the iron mined in this
-country coming from this source, though in Germany,
-Sweden and Scotland it is relatively much
-more important.</p>
-<h3><a id="species_Goethite">Goethite</a>
-<br />Fe&#8322;O&#8323;&middot;H&#8322;O
-<br /><a href="#Plate_12">Pl. 12</a></h3>
-<p>Occurs in lustrous brown to black
-orthorhombic prisms, usually terminated
-by low pyramids; hardness
-5; specific gravity 4; color brown to black; streak
-brownish-yellow; luster imperfect adamantine;
-opaque.</p>
-<p>Goethite, named for the poet Goethe, who was
-interested in mineralogy, is much less abundant
-than limonite or hematite, but occurs with
-them, when they are in veins. Its usual form
-is an orthorhombic prism with the edges beveled,
-and a low pyramid on either end. The crystals
-usually grow in clusters, making a fibrous mass,
-often radiated, in which case it is known as
-&ldquo;needle iron stone&rdquo;; or the prisms may be so
-short as to be almost scales; when, because of the
-yellowish-red color, it is called &ldquo;ruby mica&rdquo;. It
-is found in many states, including Connecticut,
-Michigan, Colorado, etc.</p>
-<div class="pb" id="Page_53">53</div>
-<h3><a id="species_Hematite">Hematite</a>
-<br />Fe&#8322;O&#8323;
-<br />Pl. <a href="#Plate_13">13</a> &amp; <a href="#Plate_14">14</a>
-<br /><i>specular iron</i></h3>
-<p>Occurs in compact, mammillary,
-botryoidal, or stalactitic masses of
-dark red to black color, or in earthy
-masses of bright to dark red; hardness
-6; specific gravity 5.2; color ochre red to
-black; streak cherry red to dark red; luster
-metallic, vitreous, or dull; opaque on thin edges.</p>
-<p>Hematite is readily distinguished from other
-red minerals by its hardness and streak. It may
-occur in crystals, which belong to the hexagonal
-system, and are usually hemihedral forms of the
-double pyramid, or rhombohedrons. These
-rhombohedrons usually have the edges beveled,
-as in <a href="#Plate_13">Pl. 13</a>, A; or are tabular in form as a result
-of the beveling of two of the opposite edges to
-such an extent that a form like <a href="#Plate_13">Pl. 13</a> B results.
-However the usual occurrence is in non-crystalline
-masses, which represent transformations
-from limonite by the loss of water of crystallization
-on the part of the limonite. In such
-cases we have fibrous, oolitic or compact masses,
-according to the form in which the limonite
-occurred. The transformation from limonite into
-hematite involves some heat to drive out the
-water of crystallization, but nothing like what is
-involved in metamorphism.</p>
-<p>Hematite is the source of 90% of the iron
-mined in this country. Part of it comes from
-the famous Clinton iron ore, a layer a foot or
-more in thickness; starting in New York State,
-and extending all down the Appalachian Mountains
-to Alabama, where it is ten or more feet
-thick and the basis of the Birmingham iron
-industries. Then there are tremendous deposits
-<span class="pb" id="Page_54">54</span>
-of earthy to compact hematite, probably
-derived from limonite, around the west end of
-Lake Superior. This latter region yields today
-around 75% of the iron for this country.</p>
-<p>Loose earthy masses of hematite are often
-known as &ldquo;ochre red,&rdquo; and were used by the
-Indians for war paint. Today the same sort of
-material is obtained by powdering hematite
-and using it for red paint. The red color in
-great stretches of rock is due to the presence of
-small amounts of hematite, acting as cementing
-material. The red of the ruby, garnet, spinel,
-and the pink of feldspars and calcite are due to
-traces of hematite.</p>
-<p>This mineral is very common and found in
-every state.</p>
-<h3><a id="species_Magnetite">Magnetite</a>
-<br />Fe&#8323;O&#8324;
-<br /><a href="#Plate_14">Pl. 14</a>
-<br /><i>Magnetic iron ore</i></h3>
-<p>Occurs in masses or in isometric
-octahedrons or dodecahedrons;
-hardness 6; specific gravity 5.8;
-color black; streak black; luster
-metallic; opaque on thin edges.</p>
-<p>Magnetite is another important ore of iron,
-and is peculiar in being strongly magnetic; its
-name being derived, according to Pliny, from
-that of the shepherd Magnes, who found his
-iron pointed staff attracted by the mineral when
-he was wandering on Mount Ida. This magnetic
-property has been repeatedly used to locate
-beds of magnetite, and is very helpful in separating
-magnetite from the &ldquo;black sands,&rdquo; of which
-it so often forms a part. These sands however
-generally have magnetite with so much titanium
-in it that they are unfit for smelting.</p>
-<div class="pb" id="Page_55">55</div>
-<p>Magnetite is found in association with igneous
-or metamorphic rocks, and often represents
-limonite or hematite which has been altered as
-the result of high temperatures. Some of it,
-in the igneous rocks especially, was undoubtedly
-in the molten magma and has crystallized out
-from the magma while it was still hot. It is the
-form of iron always indicative of former high
-temperatures. It is an ore mineral for about
-3% of the iron in this country, but in Scandinavia
-and some other countries, it plays a leading
-role as the source of iron.</p>
-<p>It is found in the Adirondack Mountains, in
-New Jersey, Pennsylvania, Arkansas, North
-Carolina, New Mexico, and California.</p>
-<h3><a id="species_Siderite">Siderite</a>
-<br />FeCO&#8323;
-<br />Pl. <a href="#Plate_13">13</a> &amp; <a href="#Plate_14">14</a>
-<br /><i>Spathic iron</i></h3>
-<p>Occurs in fibrous botryoidal
-masses or rhombohedral crystals,
-sometimes with curved faces; hardness
-3.5; specific gravity 3.8; color
-gray-brown; streak white; luster vitreous; translucent
-on thin edges.</p>
-<p>Like hematite this mineral belongs to the
-hexagonal system, and crystallizes in hemihedral
-form, making the rhombohedron. Its
-faces are often curved, which is rare in minerals,
-only a few forms like this and dolomite having
-other than plane faces. When siderite crystals
-grow in clusters, the crowding often results in
-growth on one face only, making a mass of
-fibrous character, and in such cases the surface
-of the mass is botryoidal in contour. The
-mineral is likely to oxidize, losing its gray-brown
-color, and becoming limonite. In the United
-<span class="pb" id="Page_56">56</span>
-States it is scarcely ever used as an ore for iron,
-but in Germany and England a great deal of iron
-is smelted from this mineral.</p>
-<p>It occurs in Massachusetts, Connecticut, New
-York, throughout the Appalachian Mountains,
-and also in Ohio.</p>
-<h3><a id="species_Pyrite">Pyrite</a>
-<br />FeS&#8322;
-<br />Pl. <a href="#Page_15">15</a> &amp; <a href="#Page_16">16</a>
-<br /><i>iron pyrites</i></h3>
-<p>Occurs as cubes, octahedrons and
-pyritohedrons, or in compact masses,
-scales or grains; hardness 6; specific
-gravity 5.1; color brassy yellow;
-streak greenish-black; luster metallic; opaque
-on thin edges.</p>
-<p>This is one of the commonest of all minerals.
-It is found in all kinds of rocks, with all kinds
-of associations, in all parts of the world. Its
-crystals are isometric, and cubes and octahedrons
-are abundant. The pyritohedron is also a common
-form, and characteristic of this mineral.
-It is a hemihedral form derived from a 24-sided
-form, <i>i.e.</i> the cube with four faces on each
-side. On this 24-sided form each alternate face
-has developed and the others have disappeared,
-resulting in a 12-sided form, known as the
-pyritohedron, which differs from the dodecahedron
-in that each of its faces is five-sided instead
-of rhomboidal. When in crystals pyrite can not
-be easily confused with any other mineral; but
-when in masses it is often mistaken for gold,
-chalcopyrite, pyrrhotite or marcasite. From
-the first two, the color should be sufficient to
-distinguish it, for they are golden yellow.
-Pyrrhotite is bronze yellow, and marcasite is
-paler yellow. Then too in hardness pyrite is
-<span class="pb" id="Page_57">57</span>
-much harder than any of these minerals except
-marcasite. This last is the one which is most
-likely to cause real difficulty. Its lighter color,
-and the fact that it usually comes in fibrous
-masses are the best distinctions.</p>
-<p>In spite of being so abundant pyrite is scarcely
-ever used as an ore for iron, because the sulphur
-makes the metal &ldquo;short,&rdquo; or brittle, and the sulphur
-is not easily gotten entirely out of the iron;
-but pyrite is used largely in the manufacture of
-sulphuric acid, so important to many of our
-industries.</p>
-<p>Other sulphides are commonly mixed with
-pyrite, such as chalcopyrite, arsenopyrite,
-argentite, etc.; but the most important impurity
-is gold, which is often scattered through the
-pyrite in invisible particles, and sometimes in
-quantities enough to make it worth while to
-smelt it for the gold.</p>
-<p>Pyrite is particularly the form in which the
-sulphur compounds of iron appear in rocks which
-have been highly heated, and is to be expected in
-metamorphic rocks and also igneous rocks,
-especially in fissures and veins leading from the
-igneous rocks. It may occur in sedimentary
-rocks, but in these last it is usually marcasite.</p>
-<h3><a id="species_Marcasite">Marcasite</a>
-<br />FeS&#8322;
-<br /><a href="#Plate_15">Pl. 15</a>
-<br /><i>white pyrite</i></h3>
-<p>Occurs in orthorhombic crystals,
-usually grouped to make fibrous or
-radiating masses, or non-crystalline
-in masses; hardness 6; specific gravity
-4.8; color pale brassy-yellow; streak greenish-gray;
-luster metallic; opaque on thin edges.</p>
-<p>Marcasite has the same chemical composition,
-<span class="pb" id="Page_58">58</span>
-as pyrite, and looks like it, but is lighter colored
-and usually occurs in fibrous masses. It is the
-commoner form in limestones and shales, while
-pyrite is more likely to occur in igneous and
-metamorphic rocks. It seems probable that
-marcasite is due to a more hasty precipitation
-from cold solutions, while pyrite is deposited
-more slowly from hot solutions.</p>
-<p>Isolated crystals of marcasite are rare; but, if
-formed, they belong to the orthorhombic system.
-Usually some form of twinning is present, and
-because of the multiple character of the twinning,
-marcasite crystals usually show a ragged outline,
-with reentrant angles. It is most abundant
-in radiated masses, which appear fibrous on the
-broken surfaces. It decomposes easily, taking
-oxygen from the air and forming, even in
-museum cases, a white efflorescence or &ldquo;flower,&rdquo;
-which is iron sulphate or melanterite. In moist
-air it takes water and decomposes to sulphuric
-acid which may change the surrounding limestone
-to gypsum. Marcasite is found wherever
-limestones and shales are the country rock.</p>
-<h3><a id="species_Pyrrhotite">Pyrrhotite</a>
-<br />Fe&#8321;&#8321;S&#8321;&#8322;
-<br /><i>Magnetic pyrites</i></h3>
-<p>Occurs in masses; hardness 4;
-specific gravity 4.6; color bronze;
-streak grayish-black; luster metallic;
-opaque on thin edges.</p>
-<p>Tabular crystals are known, but are very rare.
-They belong to the hexagonal system. This
-form is easily distinguished from the other yellow
-minerals by being magnetic. It is by no means
-as abundant as the two preceding sulphides of
-iron, but does occur fairly frequently in veins
-<span class="pb" id="Page_59">59</span>
-in igneous rocks, and less frequently in limestones,
-large quantities of sulphuric acid being
-made from a deposit in limestone at Ducktown,
-Tenn. It will be found in most states. When
-associated with nickel it is an important source
-for the latter mineral, as at Sudbury, Canada.
-Pyrrhotite is very like a substance found in
-meteorites, known as troilite.</p>
-<h3 class="center"><span class="sc">The Lead Group</span></h3>
-<p>After learning how to get iron from the rocks
-by rude smelting methods, the early peoples tried
-heating various rocks, and some time around 500
-<span class="small">B.C.</span> stumbled upon lead, which is rather easily
-separated from its ores. This metal was used
-through Roman times to make pipes, gutters, etc.</p>
-<p>Lead is a soft metal, fairly malleable, but with
-little ductility, and still less tensile strength.
-Though one of the commoner metals, it does not
-occur as pure metal in Nature. It is diffused in
-minute quantities through the igneous rocks, and
-also is found in the sedimentary rocks and in
-the sea water. Its minerals are few, galena, the
-sulphide of lead, being the commonest, and at
-the same time the form in which lead is primarily
-deposited. Galena may also represent a secondary
-deposition. The other minerals, cerrusite,
-anglesite, and pyromorphite are results of modification
-of the galena when it lies near enough to
-the surface to be acted on by weathering agents,
-like water and air. Lead minerals are usually
-associated with zinc minerals, there being but few
-places where the minerals of the one group occur
-<span class="pb" id="Page_60">60</span>
-without the other. Most lead when first smelted
-from its ore, contains a greater or less amount of
-silver in it, sometimes enough so that the lead ore
-is better worth working for the silver than for the
-lead.</p>
-<p>Lead is used in making pipes, gutters, bullets,
-etc., and in its oxide forms in the manufacture of
-paints and glass. Eighty-three parts of lead
-with 17 parts of antimony make type metal.
-Lead and tin alloy to make solder. Lead and
-tin with small amounts of copper, zinc and
-antimony make pewter. The United States
-produce about 20% of the world&rsquo;s supply of this
-metal.</p>
-<h3><a id="species_Galena">Galena</a>
-<br />PbS
-<br /><a href="#Plate_17">Pl. 17</a>
-<br /><i>lead glance</i></h3>
-<p>Occurs in cubes or cleavable
-masses; hardness 2.5; specific gravity
-7.5; color lead-gray; streak lead-gray;
-luster metallic; opaque.</p>
-<p>While there is quite a group of lead-gray minerals,
-galena is easily identified by its cleavage,
-which is perfect in three directions parallel to
-the cube faces. Even a moderate blow of the
-hammer will shatter a mass of galena into small
-cubic pieces. The crystals often have the corners
-cut by octahedral faces, and occasionally the
-edges are beveled by dodecahedral faces. It is
-not uncommon to find crystals of large size,
-several inches across. If galena has 1 to 2% of
-bismuth as an impurity, curiously enough, the
-cleavage changes to octahedral, but this is a rare
-occurrence.</p>
-<p>Galena may occur as a primary mineral in veins
-associated with igneous intrusions, or in irregular
-<span class="pb" id="Page_61">61</span>
-masses in metamorphic rocks; but it is more often
-found in irregular masses in limestones, where the
-limestone has been dissolved, and the cavities
-thus formed, filled with secondary deposits of
-galena. It also occurs at the contact between
-igneous rocks and the adjacent rock, whatever
-this may be. Sometimes it is found in residual
-clays.</p>
-<p>Among the most important lead deposits are
-the C&oelig;ur d&rsquo;Alene district in Idaho, where
-galena with a high percentage of silver is mined;
-the Leadville, Colo., district where lead, silver
-and gold occur together in veins; the Joplin,
-Mo., district, where lead and zinc ores occur
-together in irregular masses in limestones; and
-the Wisconsin district of similar character.</p>
-<p>When found galena is usually associated with
-sphalerite, argentite chalcopyrite, pyrite and
-calcite. It will be found in every state.</p>
-<h3><a id="species_Cerrusite">Cerrusite</a>
-<br />PbCO&#8323;
-<br /><a href="#Plate_18">Pl. 18</a>
-<br /><i>White lead ore</i></h3>
-<p>Occurs in fibrous or compact
-masses, or in orthorhombic crystals,
-usually on galena; hardness 3.5;
-specific gravity 6.5; colorless; streak
-white; luster adamantine; transparent on thin
-edges.</p>
-<p>While the crystals of this mineral simulate
-hexagonal, they are actually orthorhombic, the
-simple form being an octahedron with two of its
-edges beveled, making double six-sided pyramids
-(see <a href="#Plate_18">Pl. 18</a> A.) Usually prism faces are present.
-Twinning is common, both the simple contact
-sort, as shown on <a href="#Plate_18">Plate 18</a> B, and also the sort
-in which three crystals have grown through each
-<span class="pb" id="Page_62">62</span>
-other, so as to make a six-rayed crystal. The
-considerable weight, and the fact that it
-effervesces in acid serve to identify cerrusite.
-When pure it is colorless, but impurities cause it
-to appear white, gray or grayish-black, and
-sometimes it has a tinge of blue or green.</p>
-<p>It is likely to occur wherever galena is found,
-as a secondary mineral derived from the galena.
-In this country it is not used as an ore, for, as in
-the Leadville district, veins which have cerrusite
-near the surface change at moderate depths, and
-galena takes the place of the cerrusite. It is
-found all down the Appalachian Mountains, and
-in all the Cordilleran States. Especially fine
-specimens have come from the C&oelig;ur d&rsquo;Alene
-district in Idaho.</p>
-<h3><a id="species_Anglesite">Anglesite</a>
-<br />PbSO&#8324;
-<br /><a href="#Plate_18">Pl. 18</a></h3>
-<p>Occurs in grains and masses, or in
-tabular and prismatic orthorhombic
-crystals; hardness 3; specific gravity
-6.3; colorless; luster adamantine; transparent on
-thin edges.</p>
-<p>Two modes of occurrence are characteristic,
-one in cavities in galena, the other in concentric
-layers around a nucleus of galena. In the former
-case fine crystals are developed, in the latter the
-mineral is in masses. The crystals look like
-those of barite, but are soluble in nitric acid
-while the barite is insoluble. Sometimes the
-crystals are prismatic with pyramidal faces
-instead of the tabular form.</p>
-<p>It is found in the lead mines associated with
-galena, and in this country is not used as an ore
-for lead, but in Mexico and Australia it is
-<span class="pb" id="Page_63">63</span>
-abundant enough to be mined as an ore. Exposed
-to water which has carbon dioxide in it,
-and most surface waters have some, it readily
-changes to cerrusite. It is found in Missouri,
-Wisconsin, Kansas, Colorado, and Mexico.</p>
-<h3><a id="species_Pyromorphite">Pyromorphite</a>
-<br />Pb&#8325;Cl(PO&#8324;)&#8323;
-<br /><a href="#Plate_17">Pl. 17</a>
-<br /><i>Green lead ore</i></h3>
-<p>Occurs in small barrel-shaped
-hexagonal crystals, and in fibrous or
-earthly masses; hardness 3.5; specific
-gravity 7; color green to brown;
-luster resinous; translucent on thin edges.</p>
-<p>Pyromorphite is found in the upper levels of
-lead mines, and is formed by the decomposition
-of galena. Its green color (sometimes shading
-off toward brown), considerable weight and
-resinous luster, serve to distinguish this mineral.
-The crystal form is that of a simple hexagonal
-prism, with the ends truncated. It is found in
-Ph&oelig;nixville, Penn., Missouri, Wisconsin, Colorado,
-New Mexico, etc.</p>
-<h3 class="center"><span class="sc">The Zinc Group</span></h3>
-<p>Zinc and copper made the brass of early
-Roman times; but even then, zinc was not known
-as a separate metal, the brass being made by
-smelting rocks in which both zinc and copper
-occurred, the zinc never being isolated until
-much later. Some time in the later Roman
-times it seems to have been obtained separately,
-but then and all down through the Middle Ages
-zinc and bismuth were confused. Our earliest
-record of zinc being smelted, as we know it today,
-was about 1730 in England. In those earlier
-<span class="pb" id="Page_64">64</span>
-days, the product, zinc, or bismuth, or both
-together, were known as &ldquo;spelter,&rdquo; and this
-name has clung to zinc in mining and commercial
-circles; so that today, if one looks for quotations
-in the newspaper, he often finds zinc under the
-head of spelter.</p>
-<p>Zinc, like lead, is diffused in small quantities
-through all the igneous rocks. In places it is
-segregated in fissures or veins leading from the
-igneous rocks, along the contact between igneous
-rocks and either sedimentary or metamorphic
-rocks, in limestones where solution cavities have
-been formed and later filled with zinc minerals,
-and as a residue where limestones have been
-weathered away. In all these places it is closely
-associated with lead.</p>
-<p>The sulphide, sphalerite, is the primary
-mineral, and the other minerals, like zincite,
-smithsonite, calamine, willemite, franklinite, etc.,
-are secondary, resulting from modifications of
-the original sphalerite. In connection with zinc
-minerals the region of Franklin Furnace, N. J.,
-is especially interesting, for at that place are
-found two large metamorphosed deposits containing
-a wide range of zinc minerals, several of
-which are not found anywhere else.</p>
-<p>Zinc is soft and malleable, but is only slightly
-ductile, and has little tensile strength. It alloys
-with several metals, and in this form is most
-useful today; three parts of copper to one of
-zinc making brass; four or more parts of copper
-and one of zinc, making &ldquo;gold foil&rdquo;; copper and
-zinc (a little more zinc than copper) making
-&ldquo;white metal&rdquo;; three parts of copper to one of
-<span class="pb" id="Page_65">65</span>
-zinc and one of nickel making German silver;
-etc. Zinc is also used in large quantities in
-galvanizing iron, sheets of iron being dipped
-into melted zinc and thus thinly coated. It is
-also used in batteries and a wide range of chemical
-industries.</p>
-<h3><a id="species_Sphalerite">Sphalerite</a>
-<br />ZnS
-<br />Pl. <a href="#Page_19">19</a> &amp; <a href="#Page_20">20</a>
-<br /><i>zinc blende, black jack</i></h3>
-<p>Occurs in grains, in fibrous or
-layered masses, or in isometric crystals;
-hardness 3.5; specific gravity
-4; color yellow-brown to almost
-black; streak light yellow to brownish;
-luster resinous to adamantine; translucent
-on thin edges.</p>
-<p>When in crystals sphalerite occurs most commonly
-either in dodecahedrons or in tetrahedrons
-(hemihedral forms of the isometric octahedron).
-The cleavage is fairly good and parallel to the
-faces of the dodecahedron. The difficulty
-usually is to get large enough crystalline masses
-to see this cleavage clearly, but by examining
-the angles between the faces of cleavage pieces
-they will be found to be the same as those on a
-dodecahedron. When the mineral is pure, it has
-the color of resin, but sometimes it is reddish
-to red-brown, and then it is called &ldquo;ruby zinc,&rdquo;
-more often it is dark brown due to the presence of
-iron as an impurity. This is what the miners
-call &ldquo;black-jack.&rdquo; The presence of iron also
-tends to make the streak darker. The hardness,
-streak and cleavage will usually determine this
-mineral readily.</p>
-<p>Sphalerite is the primary ore of zinc and is
-usually found in fissures and veins leading from
-<span class="pb" id="Page_66">66</span>
-masses of igneous rocks, or along the surface of
-contact where igneous rocks like granite or lavas
-come against such metamorphic rocks as gneisses,
-schists, or crystalline limestones. In the
-region of Joplin, Mo., however, the sphalerite is
-of secondary character, having been gathered by
-waters circulating through the limestones, and
-deposited in them in irregular pockets. This
-Joplin district has produced more zinc than any
-other in the world. The United States annually
-produces about 25% of the world&rsquo;s supply of this
-metal.</p>
-<p>Sphalerite is always associated with galena,
-and such other minerals as argentite, pyrite,
-chalcopyrite, fluorite, quartz, calcite and barite,
-are very apt to be present. It will be found in
-almost every state, especially in fissures and
-veins, and less frequently in cavities in limestones.</p>
-<h3><a id="species_Zincite">Zincite</a>
-<br />ZnO
-<br />Pl. <a href="#Page_19">19</a> &amp; <a href="#Page_20">20</a>
-<br /><i>red zinc ore</i></h3>
-<p>Usually occurs massive, but may
-be found in crystals; hardness 4;
-specific gravity 5.6; color deep red;
-streak orange; luster subadamantine;
-translucent on thin edges.</p>
-<p>When in crystals zincite forms in hexagonal
-prisms with hexagonal pyramids on the ends.
-This is rather rare, most of the zincite being
-found in massive form. The cleavage is parallel
-to the prism faces and perfect. The deep red
-color and orange streak are wholly
-characteristic.</p>
-<p>This mineral is so common at Franklin Furnace,
-N. J., as to be an important ore, but it is
-very seldom found elsewhere. This district, as
-<span class="pb" id="Page_67">67</span>
-mentioned before, is a peculiar one for zinc
-minerals. The zinc beds are in a metamorphosed
-limestone, and into this are intruded
-numerous dikes of granite. Probably the zinc
-was originally present in the bed of limestone
-as smithsonite, calamine and other secondary
-minerals of zinc. When intruded by the hot
-granite the smithsonite (carbonate) may well
-have been altered to the oxide, zincite; while the
-calamine (hydrous silicate) became the simple
-silicate, willemite.</p>
-<h3><a id="species_Willemite">Willemite</a>
-<br />ZnSiO&#8324;
-<br /><a href="#Plate_20">Pl. 20</a></h3>
-<p>Occurs in masses or in crystals;
-hardness 5.5; specific gravity 4.1;
-color pale yellow when pure; luster
-resinous; translucent on thin edges.</p>
-<p>Willemite is another of the minerals which are
-distinctively characteristic of Franklin Furnace,
-and found elsewhere very rarely. It is so common
-there as to be one of the principal ores, and
-mostly occurs in irregular masses, but is also
-found in crystals. These are hexagonal prisms,
-with a three-sided (rhombohedral) pyramid on
-the ends. The color when pure is whitish or
-greenish-yellow, but with small amounts of
-impurities it may be flesh-red, grayish-white or
-yellowish-brown. When in crystals it is easily
-determined; but when massive it looks like
-calamine, and can only be distinguished by placing
-a bit of the mineral in a closed tube and
-heating it, in which case calamine will give off
-water vapor, while willemite will not.</p>
-<p>This mineral is one of those resulting from
-metamorphic alteration and is derived from
-<span class="pb" id="Page_68">68</span>
-calamine, when the latter loses its water of
-crystallization. It is common at Franklin
-Furnace, N. J., and also found occasionally
-elsewhere, as at Salida, Colo., and in Socorro Co.,
-New Mexico.</p>
-<h3><a id="species_Calamine">Calamine</a>
-<br />Zn&#8322;(OH)&#8322;&middot;SiO&#8323;</h3>
-<p>Occurs as crystalline linings in
-cavities, or as botryoidal or stalactitic
-masses; hardness 5; specific gravity 3.4; colorless
-to white; luster vitreous.</p>
-<p>Calamine resembles both smithsonite and
-willemite when in non-crystalline masses. From
-the smithsonite it is easily separated by the
-fact that in nitric acid the smithsonite effervesces
-and the calamine does not. From willemite it is
-harder to distinguish, but a piece may be placed
-in a closed tube and heated. If it is calamine
-water vapor will be given off, if willemite nothing
-happens. When calamine occurs in crystals
-these are orthorhombic and mostly tabular, and
-the crystals are peculiar in that the two ends are
-terminated differently.</p>
-<p>Both this and smithsonite are secondary
-minerals and usually occur together when zinc is
-found in limestones. It is abundant at Franklin
-Furnace and Sterling Hill, N. J., and also found
-at Ph&oelig;nixville, Penn., in Wythe Co., Va., and
-Granby, Mo.</p>
-<h3><a id="species_Smithsonite">Smithsonite</a>
-<br />ZnCO&#8323;
-<br /><a href="#Plate_21">Pl. 21</a>
-<br /><i>Dry bone</i></h3>
-<p>Usually occurs as incrustations,
-grains, earthy or compact masses,
-and as crystals; hardness 5; specific
-gravity 4.4; color white, yellow,
-greenish or bluish; streak white; luster vitreous;
-transparent on thin edges.</p>
-<div class="pb" id="Page_69">69</div>
-<p>When pure this mineral is colorless, but, as it
-occurs, it is usually white, or tinged with some
-shade of yellow, green, or blue, but in all cases its
-streak is white. The crystals are rhombohedrons
-often with edges beveled or corners cut by other
-faces. It resembles calamine and willemite, but
-is readily separated from either of these by the
-acid test, for smithsonite effervesces when acid
-is placed on it.</p>
-<p>Next to sphalerite, smithsonite is the commonest
-of the zinc minerals. It is a secondary
-mineral, resulting from the action of lime-charged
-water acting on sphalerite, and so is
-likely to be found wherever zinc minerals occur
-in a limestone region. In the Wisconsin-Illinois-Iowa
-district it serves as a minor ore of zinc, and
-is termed here &ldquo;dry bone.&rdquo; It is also found in
-the Missouri and Arkansas districts, and in
-Europe is an important ore for zinc.</p>
-<h3><a id="species_Franklinite">Franklinite</a>
-<br />(ZnMn)Fe&#8322;O&#8324;
-<br /><a href="#Plate_21">Pl. 21</a></h3>
-<p>Occurs in compact grains or
-masses, and in isometric octahedrons;
-hardness 6; specific gravity
-5; color black; streak reddish-brown; luster
-metallic; opaque on thin edges.</p>
-<p>This is a mineral peculiar to the Franklin Furnace
-region, from which it gets its name. It
-looks like magnetite, but its reddish-brown
-streak and lack of magnetism distinguish it.
-When it occurs in octahedrons, the edges are
-rounded, while those of magnetite are sharp. It
-is a complex and variable oxide of zinc, iron and
-manganese, which has resulted from the metamorphism
-of the beds in which it occurred
-<span class="pb" id="Page_70">70</span>
-probably being originally something quite
-different.</p>
-<h3 class="center"><span class="sc">The Manganese Group</span></h3>
-<p>Though manganese was known in the mineral
-pyrolusite in early times, it was then thought to
-be magnetite or magnetic iron ore. It was not
-until 1774 that it was isolated and recognized
-as a distinct element.</p>
-<p>Manganese is one of the lesser elements in the
-crust of the earth, making less than .07 of one
-percent, but as an alloy with other metals,
-especially iron, it has attained a considerable
-importance to man. It is used chiefly with iron,
-20% of manganese making the alloy, spiegeleisen,
-a combination which occurs in Nature in Germany,
-and from 20% to 80% making ferromanganese.
-These alloys are in great demand
-because they make an especially tough steel essential
-in the manufacture of munitions. The
-sources for manganese are the oxide ores, manganite,
-pyrolusite and psilomelane, which have
-been formed as secondary minerals, as a result of
-the weathering of silicates which carry manganese.
-They occur widely enough, but throughout
-the United States the deposits are small, and this
-is one of the elements in which this country is not
-self-sufficient. The largest producer of manganese
-is Russia; however she consumes almost all of her
-output at home, and our supply comes from the
-next largest producers, India, the Union of South
-Africa, and the Gold Coast. A shift in trade may
-be expected when Brazil&rsquo;s recently discovered ore
-body in Matto Grosso is brought into full production.
-<span class="pb" id="Page_71">71</span>
-Besides being used as an alloy, manganese is
-employed in making paints and dyes, for clearing
-glass, and for some types of electric batteries.</p>
-<h3><a id="species_Pyrolusite">Pyrolusite</a>
-<br />MnO&#8322;</h3>
-<p>Occurs in earthy or fibrous masses;
-hardness 1-2; specific gravity 4.8;
-color black; streak black; luster
-dull; opaque.</p>
-<p>Pyrolusite occurs in soft masses and incrustations,
-usually leaving a sooty mark on the fingers.
-Sometimes it seems to be in crystals, but these
-are pseudomorphs which have the form of manganite,
-from which the pyrolusite has formed as a
-result of the water having been driven from the
-manganite. Frequently pyromorphite and manganite
-will be found together, and in some cases
-the outer part of a mass or crystal will be pyrolusite,
-while the center is still manganite. Psilomelane
-is another oxide of manganese with
-water and may appear very like pyrolusite, but
-both manganite and psilomelane have much
-greater hardness than does pyrolusite. If there
-is difficulty in deciding about pyrolusite, it may
-be placed in a closed tube and heated. It will
-not be affected by the heat, while, under the
-same circumstances, both manganite and psilomelane
-will give off water vapor.</p>
-<p>Pyrolusite usually occurs in black streaks or
-pockets in residual clays which have formed as a
-result of the decomposition of limestones. It
-may also occur in dendritic forms in seams and
-crevices (see manganite). It is found in Vermont,
-Massachusetts, Virginia, Arkansas, Colorado,
-California, etc.</p>
-<div class="pb" id="Page_72">72</div>
-<h3><a id="species_Psilomelane">Psilomelane</a>
-<br />MnO&#8322;&middot;H&#8322;O</h3>
-<p>Occurs in compact botryoidal or
-stalactitic masses; hardness 5-6;
-specific gravity 4.2; color black;
-streak brownish-black; luster metallic; opaque
-on thin edges.</p>
-<p>Psilomelane is very like pyrolusite, and often
-occurs with it. It is distinguished by its greater
-hardness, and the fact, that when heated in a
-closed tube, it gives off water vapor. From
-manganite it is more easily distinguished, for it
-never occurs in crystals, while the manganite is
-usually crystalline. This and pyrolusite are the
-principal ores of manganese.</p>
-<p>Wad is an impure form of psilomelane, having
-some iron oxide mixed with the manganese oxide,
-usually limonite; or the impurity may take the
-form of a copper, cobalt, lithium or barium
-oxide.</p>
-<p>Psilomelane is found at Brandon, Vt., in
-Arkansas, Colorado, California, etc.</p>
-<h3><a id="species_Manganite">Manganite</a>
-<br />Mn&#8322;O&#8323;&middot;H&#8322;O
-<br /><a href="#Plate_22">Pl. 22</a></h3>
-<p>Occurs in prismatic crystals, or in
-columnar or fibrous masses; hardness
-4; specific gravity 4.4; color
-steel gray; streak reddish-black; luster submetallic;
-opaque on thin edges.</p>
-<p>This is the form taken by manganese oxide
-when it crystallizes in the presence of moisture,
-and pyrolusite frequently changes to manganite
-when exposed to moisture. The crystals are
-orthorhombic prisms, with striated sides and the
-ends truncated. These prisms usually occur in
-bundles and give the mineral a fibrous appearance.
-Manganite is not hard to identify, the
-<span class="pb" id="Page_73">73</span>
-striations on the crystals and the streak being
-very characteristic.</p>
-<p>In seams and tiny crevices this mineral, and
-often pyrolusite, grows in a branching manner,
-resembling tree-like or &ldquo;mossy&rdquo; masses. This is
-termed dendritic, and the growths of manganese
-minerals are called dendrites. One of the most
-curious of these is when the &ldquo;mossy&rdquo; growth is
-inclosed in chalcedony, making the so-called <i>moss
-agate</i>. These moss agates are abundant through
-the Rocky Mountains and are frequently cut for
-semi-precious stones. The finest ones however
-come from India and China.</p>
-<p>Manganite is found in the Lake Superior
-region, Colorado, etc.</p>
-<h3><a id="species_Rhodochrosite">Rhodochrosite</a>
-<br />MnCO&#8323;</h3>
-<p>Occurs in compact cleavable
-masses; hardness 4; specific gravity
-3.5; color rose to dark red; streak
-white; luster vitreous; translucent on thin edges.</p>
-<p>This usually occurs in pink to red masses which
-cleave readily parallel to the faces of the rhombohedron.
-When it is found in crystals, which
-are rare, these too are rhombohedrons. It is
-usually found in veins as a gangue mineral with
-copper, silver or zinc ores. Its beautiful color and
-the fact that it effervesces in acid serve to distinguish
-this mineral. It is found at Branchville,
-Conn., at Franklin Furnace, N. J., and in veins
-with silver in Colorado, Nevada, and Montana.</p>
-<h3 class="center"><span class="sc">The Aluminum Group</span></h3>
-<p>Though aluminum is one of the most abundant
-of all the metals, making some 8% of the crust of
-<span class="pb" id="Page_74">74</span>
-the earth, its union with other elements is so
-firm, that only recently have methods been
-found for getting the metal free. It was first
-isolated in 1846, but up to 1890 the extraction of
-aluminum was so expensive, that it could not be
-widely used. About that time electrical processes
-were applied to its extraction, and since then the
-price has steadily dropped, until now it is under
-$.20 per pound. It is very malleable, and ductile,
-and has high tensile strength. Exposed to
-the air, water or ordinary gases, it does not
-tarnish; and it is very light, an equal bulk weighing
-about a third as much as iron. The combination
-of lightness and strength, and the fact
-that it is a good conductor of electricity, have
-made it available for a wide range of uses, such
-as electrical apparatus, delicate instruments,
-boats, aeroplanes, and domestic utensils.</p>
-<p>It is an essential component of all the important
-rocks, except sandstone and limestone, and
-combines to a greater or less degree in a host of
-minerals. Though present in clays, shales,
-argillites, feldspars, and micas, it is only from
-bauxite that it has been successfully extracted.
-Aside from the small number of simple compounds
-of aluminum grouped here, it also takes
-a part in the make-up of a large series of minerals
-termed silicates, treated a little further on in
-this book.</p>
-<p>It alloys with other metals, especially copper.
-The union of copper and a small amount of
-aluminum makes aluminum-bronze, which looks
-like gold and is used for watch chains, pencil-cases,
-etc., and also for the antifriction bearings
-<span class="pb" id="Page_75">75</span>
-of heavy machinery. A small amount added to
-steel prevents air holes and cracks in casting.</p>
-<h3><a id="species_Corundum">Corundum</a>
-<br />Al&#8322;O&#8323;
-<br /><a href="#Plate_23">Pl. 23</a></h3>
-<p>Occurs in cleavable masses or in
-hexagonal crystals; hardness 9;
-specific gravity 4; colorless, red,
-yellow, blue, or gray; luster vitreous to adamantine;
-translucent to transparent on thin
-edges.</p>
-<p>Corundum is readily recognized by its hardness,
-second only to that of the diamond. The
-crystals may be simple six-sided prisms, hexagonal
-pyramids or combinations of the two.
-The cleavage is usually described as parting, for
-it is by no means perfect, but when it is recognizable
-it is parallel to the faces of a rhombohedron,
-and cleavage pieces may appear almost cubic.</p>
-<p>When in clear and perfect crystals this mineral
-is one of the most highly prized of all the gems.
-Clear and colorless it is known as the &ldquo;<i>Oriental
-white sapphire</i>&rdquo;; when tinged with blue it is the
-<i>sapphire</i>; when colored yellow, the &ldquo;<i>Oriental
-topaz</i>&rdquo;; when green, the &ldquo;<i>Oriental emerald</i>&rdquo;;
-when purple, the &ldquo;<i>Oriental amethyst</i>&rdquo; and when
-red, the <i>ruby</i>. Sapphires range from colorless
-to deep blue, the value depending on the shade
-of the blue, and increasing as the color deepens.
-The Oriental topaz can easily be confused with
-the true topaz, which is a much commoner and
-less valuable gem, but can be distinguished by
-the hardness, topaz having a hardness of but 8.
-The name emerald is applied to several green
-gems, mostly to beryl, which is not so hard and
-is the true emerald. The Oriental emeralds have
-<span class="pb" id="Page_76">76</span>
-a value about the same as diamonds. Rubies of
-clear and deep color are the rarest of all gems,
-ranging in value about three times as high as
-diamonds of equal size. The most sought-for
-shade is the so-called &ldquo;pigeon-blood red,&rdquo; and
-the value of a stone of this sort is almost dependent
-on the whim of the buyer. The best of
-the rubies come from granites or metamorphosed
-limestones in Burma; the best sapphires from
-Ceylon, though both of these, and some of the
-other corundums of gem quality, have been
-found in North Carolina and Montana.</p>
-<p>Around these stones, which have been used so
-long among the Hindus, Persians, Jews, Egyptians,
-and Christians, a wealth of lore has been
-woven. The sapphire was Saturn&rsquo;s stone, and a
-talisman to attract Divine favor. Where tradition
-makes the stone on which the ten commandments
-were written the sapphire, it is probable
-that, what was really meant, is lapis lazuli,
-as is also the case when sapphires are mentioned
-as building stones for the celestial gates. The
-ruby in ancient lore is termed &ldquo;lord of stones,&rdquo;
-&ldquo;gem of gems&rdquo; etc., and so protected its wearer
-that he was safe from injury in peace or war.</p>
-<p>When corundum is colored brown by impurities
-of iron, it is termed <i>corundum</i>, when black
-by greater quantities of iron, it is <i>emery</i>. These
-varieties are far the commonest form in which
-corundum occurs, and when ground to finer or
-coarser powder make the commercial emery.
-Emery is likely to be found in sands, making so-called
-&ldquo;black sands,&rdquo; where it has accumulated
-as a result of the weathering to bits corundum-bearing
-<span class="pb" id="Page_77">77</span>
-rocks. In some one of its forms, corundum
-is found in Massachusetts, Connecticut,
-New York, New Jersey, and all down the Appalachian
-Mountains, also in Colorado, Montana,
-California, etc.</p>
-<h3><a id="species_Bauxite">Bauxite</a>
-<br />Al&#8322;O&#8323;&middot;2H&#8322;O</h3>
-<p>Occurs in grains, or oolitic or
-clay-like masses; hardness 1-3; specific
-gravity 2.5; color white to yellowish-white
-or reddish-brown.</p>
-<p>Bauxite never comes in crystals, but is usually
-in earthy masses, which have resulted from the
-decomposition of granitic or volcanic rocks, in
-circumstances where hot alkaline waters were
-present. This explanation seems to apply
-especially to the deposits in France, which were
-first the chief source of the bauxite, and may be
-applicable to those in Georgia and Alabama.
-Some of the other deposits, however, do not
-seem to have had any hot water available, and
-the deposit appears more like simple decomposition
-of the underlying rocks by alkaline
-waters.</p>
-<p>In many cases bauxite resembles limonite in
-being a mixture of two or more aluminum oxides
-with water of crystallization, such as Al&#8322;O&#8323;&middot;H&#8322;O,
-Al&#8322;O&#8323;&middot;2H&#8322;O and Al&#8322;O&#8323;&middot;3H&#8322;O. This is particularly
-true of the bauxite which resulted from
-the decomposition of rocks by surface water.</p>
-<p>Bauxite is the ore from which aluminum is
-obtained. The deposits are not large, but the
-United States has its share of them. It is found
-in Alabama, Arkansas, Georgia, Missouri, Tennessee,
-and California.</p>
-<div class="pb" id="Page_78">78</div>
-<h3><a id="species_Cryolite">Cryolite</a>
-<br />Na&#8323;AlF&#8326;
-<br /><i>Ice stone</i></h3>
-<p>Occurs in pseudo-cubic crystals or
-massive; hardness 2.5; specific gravity
-3; color white; luster vitreous;
-transparent on thin edges.</p>
-<p>Cryolite is a relatively soft mineral, colorless
-to white as snow; for which reason, and partly
-also because it comes mostly from Greenland
-it is called &ldquo;ice stone.&rdquo; It is really monoclinic
-but the inclination of the c axis is so slight, that,
-unless examined carefully, the crystals appear
-to be cubic. Until about 1900 great quantities
-of this mineral were shipped from West Greenland,
-and from them the metal aluminum was
-extracted. When bauxite was discovered, it was
-found to be considerably cheaper to make the
-aluminum from that mineral, and now cryolite
-is no longer sought. Aside from its occurrence
-in Greenland some cryolite is found in Colorado,
-near Pike&rsquo;s Peak.</p>
-<h3 class="center"><span class="sc">The Arsenic Group</span></h3>
-<p>The metal, arsenic, is a dark steel gray in
-color, when the surface is fresh, but it soon tarnishes.
-It is very brittle and easily powdered
-under the hammer, and its only use as a metal,
-is for an alloy with lead in making shot. Its
-compounds find a wider use. The white powder
-called &ldquo;arsenic&rdquo; is arsenous acid, and is used
-mostly in making poisons, which fortunately
-are easily detected in animal tissues. Copper
-arsenate, (<i>Scheele&rsquo;s green</i>) is a pigment used in
-making green paint, and formerly in the green
-colors of wall paper. A combination of arsenous
-acid, copper oxide and acetic acid is the well
-<span class="pb" id="Page_79">79</span>
-known <i>Paris Green</i>, so much used for an insecticide.
-Beside these uses, arsenic serves a large
-number of other purposes, as in making glass
-and enamel, embalming fluids, and various
-medicines.</p>
-<p>Curiously arsenic plays a double part, acting
-part of the time as a metal, as in the two following
-minerals, and part of the time as a non-metal,
-as in cobaltite, niccolite, etc.</p>
-<h3><a id="species_Arsenopyrite">Arsenopyrite</a>
-<br />FeAsS
-<br /><a href="#Plate_24">Pl. 24</a></h3>
-<p>Occurs in well formed crystals,
-grains, or masses; hardness 5.5;
-specific gravity 6; color silver-white;
-streak black; luster metallic; opaque on thin edges.</p>
-<p>When in crystals, they are usually short prisms
-of the orthorhombic system, either end being
-terminated with a low roof. Though usually
-described as silver-white in color, there is always
-a brassy cast to the color. Its appearance is
-much like cobaltite and smaltite, but it can be
-easily distinguished from both these by putting
-a piece in nitric acid. The arsenopyrite will not
-materially change the color of the fluid, but the
-other two turn it rose-red, and all give off the
-smell of sulphur. It looks sometimes like marcasite,
-but that is yellower, and has the fibrous
-structure, not found in arsenopyrite.</p>
-<p>It is found in veins or in metamorphic rocks,
-associated with argentite, galena, sphalerite,
-chalcopyrite and pyrite. It is distinctly a
-mineral formed by deposition from hot vapors or
-hot water rising from either lavas, or in the
-course of metamorphism.</p>
-<p>It is found in New Hampshire, Vermont,
-<span class="pb" id="Page_80">80</span>
-Massachusetts, Connecticut, New York, New
-Jersey, California, etc.</p>
-<h3><a id="species_Realgar">Realgar</a>
-<br />AsS
-<br /><a href="#Plate_24">Pl. 24</a></h3>
-<p>Occurs in incrustations or scattered
-grains; hardness 1.5 to 2; specific
-gravity 3.5; color orange; streak
-orange; luster resinous; opaque on thin edges.</p>
-<p>Crystals are very rare, but when found are
-short monoclinic prisms. The color is aurora-red,
-changing to orange as soon as it is exposed
-to the air. This and the streak are entirely
-characteristic. It is a mineral associated with
-hot vapors or hot waters, and is found about
-volcanoes, as deposits from the hot water of the
-geysers in Norris Basin, Yellowstone Park, and
-in veins, associated with barite, stibnite, quartz,
-etc., as in Massachusetts, Utah, California, etc.</p>
-<h3><a id="species_Orpiment">Orpiment</a>
-<br />As&#8322;S&#8323;</h3>
-<p>Occurs as incrustations or
-powdery masses; hardness 1 to 2;
-specific gravity 3.5; color lemon
-yellow; streak yellow; luster resinous.</p>
-<p>This mineral is very like realgar in its physical
-properties, and likely to occur with it. It gives
-the lemon yellow color to the basins about hot
-springs, as in the Yellowstone Park, and about
-volcanoes. It also comes in veins with realgar.</p>
-<h3 class="center"><span class="sc">Molybdenum</span></h3>
-<p>Molybdenum is a rare metal, silvery-white in
-color, brittle and very difficult to fuse. It is used
-mostly as an alloy of steel, to make certain
-grades of tool steel. The world&rsquo;s greatest supply
-is obtained from Climax, Colorado, where the
-principal ore mineral is molybdenite.</p>
-<div class="pb" id="Page_81">81</div>
-<h3><a id="species_Molybdenite">Molybdenite</a>
-<br />MoS&#8322;</h3>
-<p>Occurs in scales or scaly masses,
-occasionally in tabular hexagonal
-crystals; hardness 1.5; specific gravity
-4.7; color lead-gray; streak bluish-gray;
-luster metallic; opaque.</p>
-<p>This mineral is the chief source for the metal
-molybdenum. Its extreme softness and greasy
-feel will distinguish it at once from any other
-mineral except graphite, which has much the
-same qualities, but its scaly character and the
-more bluish tinge in streak and color will distinguish
-these two.</p>
-<p>It occurs in granites, gneisses, and metamorphic
-rocks in Colorado, New Mexico, Maine,
-Connecticut, New Hampshire, New York, Pennsylvania,
-etc.</p>
-<h3 class="center"><span class="sc">Antimony</span></h3>
-<p>Antimony is another hard, brittle metal, of
-bluish-white color. Exposed to the air at ordinary
-temperatures it does not tarnish; and this
-combined with its hardness make it useful for
-such alloys as Britannia metal, type metal, and
-pewter. Only one of its minerals, stibnite, is
-common enough for mention.</p>
-<h3><a id="species_Stibnite">Stibnite</a>
-<br />Sb&#8322;S&#8323;
-<br /><a href="#Plate_25">Pl. 25</a>
-<br /><i>gray antimony</i></h3>
-<p>Occurs in prismatic or needle-like
-crystals; hardness 2; specific gravity
-4.5; color lead-gray; streak lead-gray;
-luster metallic; opaque.</p>
-<p>The crystals of stibnite are orthorhombic
-and usually elongated,
-the sides striated and the ends with low pyramids
-<span class="pb" id="Page_82">82</span>
-on them. Sometimes the long crystals are
-curved or even twisted. There is a well-developed
-cleavage parallel to face b in the figure.
-While the color is similar to that of galena, the
-form and cleavage are so different that stibnite
-is easily determined.</p>
-<p>The ancients used stibnite to color their eyebrows,
-now it is the source for the metal antimony.
-Hungary and Japan are famous for the
-fine large crystals they produce; but moderate
-sized crystals may be found in this country. It
-occurs in veins along with pyrite, galena, cinnabar,
-and realgar, with quartz, calcite or barite
-as gangue minerals.</p>
-<p>Stibnite has been found in Arkansas, California,
-Nevada, and Utah.</p>
-<h3 class="center"><span class="sc">The Nickel Group</span></h3>
-<p>Nickel as a metal is silvery-white in color,
-rather hard, and does not tarnish when exposed
-to the air. When pure it is malleable and fairly
-ductile. It is highly useful for plating other
-metals to protect their surfaces. Alloyed with
-steel, it makes a product of extreme hardness.
-Copper, zinc, and nickel make the well known
-German silver.</p>
-<p>Nickel has a fairly large range of minerals,
-but they do not occur with any abundance in
-the United States, so that we have to import
-most all of our nickel. In the earlier days New
-Caledonia produced most of the world&rsquo;s supply,
-but recently since the finding of large nickel
-deposits near Sudbury, Canada, this locality has
-<span class="pb" id="Page_83">83</span>
-not only outstripped New Caledonia, but now
-produces four-fifths of the world&rsquo;s supply. In
-this country but two nickel minerals will be
-found at all common.</p>
-<h3><a id="species_Niccolite">Niccolite</a>
-<br />NiAs
-<br /><a href="#Plate_25">Pl. 25</a>
-<br /><i>copper nickel</i></h3>
-<p>Occurs in masses; hardness 5.5;
-specific gravity 7.4; color pale coppery-yellow;
-streak pale brownish-black;
-luster metallic; opaque on thin edges.</p>
-<p>Niccolite is very seldom in crystals, but if
-they do occur they are hexagonal. The mineral
-looks a little like smaltite, but in case there is
-any question of the determination, dissolve a
-piece in nitric acid, and if niccolite, it will color
-the solution green.</p>
-<p>Niccolite is usually associated with copper
-and silver ores, and in this country has been
-found at Chatham, Conn., and Silver Cliff,
-Colo. It may be associated with pentlandite, a
-sulphide of iron and nickel, which is similar in
-appearance, but not so hard, and occurs in small
-grains throughout dark lavas. The particles of
-pentlandite are however so small, that they are
-seldom noticeable, but at Sudbury, Canada, this
-is the chief ore of nickel.</p>
-<h3><a id="species_Millerite">Millerite</a>
-<br />NiS
-<br /><i>capillary pyrites</i></h3>
-<p>Occurs in needle-like or fibrous
-crystals; hardness 3.5; specific gravity
-5.5; color brass-yellow; streak
-greenish black; luster metallic;
-opaque on thin edges.</p>
-<p>The fibrous crystals of millerite belong to the
-orthorhombic system. The color and streak
-suggest pyrite, but the crystals are long and
-<span class="pb" id="Page_84">84</span>
-slender, while pyrite is in cubes, octahedrons,
-etc. If there is any doubt of the identity of this
-form, place a piece in nitric acid, and if it is
-millerite, it will color the acid green.</p>
-<p>It may occur in veins associated with cobalt
-and silver minerals, or as a secondary mineral as
-at Gap Mine, Penn., or in cavities in sedimentary
-rocks. In the last case it usually is in
-needle-like crystals growing through calcite
-crystals, as at St. Louis, Mo., Keokuk, Iowa,
-and Antwerp, N. Y.</p>
-<h3 class="center"><span class="sc">The Cobalt Group</span></h3>
-<p>As a metal, cobalt is hard, brittle, and of a
-grayish color, tinged with red. It was not recognized
-as a separate element until 1735, and
-even today is one of the minor metals. Cobalt,
-chromium and a little tungsten make the alloy
-stellite, which has come into large use in making
-high-speed tools. The oxide of cobalt (CoO) is
-&ldquo;smalt,&rdquo; used to give the blue color to porcelain,
-pottery, glass, tiles, etc. Invisible ink is made by
-diluting cobalt chloride in a large quantity of
-water. This solution is a faint pink color and
-practically invisible on paper, but if heated it
-loses water and turns blue in color, and is perfectly
-visible.</p>
-<p>Cobalt is another of the metals, of which the
-United States does not have an adequate supply.
-Sweden, Norway and India were the chief
-sources of supply until cobalt was found near the
-town of Cobalt in Ontario, Canada, and now
-this district furnishes 90% of the world&rsquo;s supply.</p>
-<div class="pb" id="Page_85">85</div>
-<h3><a id="species_Cobaltite">Cobaltite</a>
-<br />CoAsS
-<br /><a href="#Plate_26">Pl. 26</a>
-<br /><i>cobalt glance</i></h3>
-<p>Usually crystalline in cubes, pyritohedrons
-or octahedrons; hardness
-5.5; specific gravity 6.1; color reddish
-silver-white; streak grayish-black;
-luster metallic; opaque on thin edges.</p>
-<p>In color cobaltite may appear very like arsenopyrite,
-especially if the reddish tinge is not
-strong, in which case the mineral can be definitely
-determined by putting a piece in nitric
-acid. If it is cobaltite the solution will be
-colored rose-red, if arsenopyrite there will be no
-change of color. The forms of the crystals are
-the same as those of pyrite, but the color will
-easily distinguish cobaltite from pyrite. This
-pink color is characteristically present either in
-or about cobalt minerals, being sometimes called
-&ldquo;cobalt bloom.&rdquo; It is a cobalt-arsenic-oxide
-with water of crystallization (Co&#8323;As&#8322;O&#8328;&middot;8H&#8322;O),
-which results from the exposure of cobalt and
-arsenic minerals to air and moisture. It is the
-pink color on the figures of both cobaltite and
-smaltite. In Sweden, Norway and India, this is
-the chief ore for cobalt, but in the United States
-it is rather rare, but is found in Oregon, and at
-Cobalt, Canada.</p>
-<h3><a id="species_Smaltite">Smaltite</a>
-<br />(CoNi)As&#8322;
-<br /><a href="#Plate_26">Pl. 26</a>
-<br /><i>gray cobalt ore</i></h3>
-<p>Usually occurs in masses; hardness
-5.5; specific gravity 6.2; color
-tin-white to steel-gray; streak grayish-black;
-luster metallic; opaque
-on thin edges.</p>
-<p>While very like cobaltite, smaltite is almost
-never found in crystals, but when crystals are
-found, they are cubes. The color is tin-white
-<span class="pb" id="Page_86">86</span>
-but there is usually a pink tinge visible due to the
-presence of small amounts of &ldquo;cobalt bloom.&rdquo;
-If in any doubt about the determination of this
-mineral, put a piece in nitric acid. If it colors
-the acid rose-pink, and is non-crystalline it is
-pretty surely smaltite; if the acid is not affected
-it is arsenopyrite.</p>
-<p>Smaltite is found in Kentucky, Missouri,
-Colorado, Idaho, California, and at Cobalt in
-Canada.</p>
-<h3 class="center"><span class="sc">Chromium</span></h3>
-<p>This metal gets its name in recognition of the
-many colors (<i>chroma</i> &ldquo;color&rdquo;), in which its
-compounds appear. Chromic oxide is a vivid
-green, used to color porcelains, pottery, tiles,
-etc., and also as a substitute for the arsenical
-greens formerly used in wall-paper. The chromate
-of lead is the pigment, well known to artists
-as &ldquo;chrome yellow,&rdquo; and the bichromate of
-potassium is bright red. The metal is obtained
-in at least two different forms; one hard, brittle
-and so resistant to heat as to be infusible at
-temperatures which would volatilize platinum;
-the other as a powder which burns brightly if
-heated in air. While used in paints, dyes, etc.,
-its greatest importance is for the making of
-ferro-chrome steel, which is used where resistance
-to sudden shock is required, as in armor
-plate, automobile springs, ball bearings, etc.
-With tungsten and cobalt it makes the alloy,
-stellite, as noted above.</p>
-<p>Chromium was used in relatively small quantities
-<span class="pb" id="Page_87">87</span>
-before the first world war, and we imported
-our supplies from Turkey, India, New Caledonia,
-and Rhodesia. During the last war we started a
-large-scale development of low-grade ores in
-Montana, and can now supply all of our needs
-from this source.</p>
-<h3><a id="species_Chromite">Chromite</a>
-<br />FeCr&#8322;O&#8324;
-<br /><i>chromic iron</i></h3>
-<p>Occurs in grains, masses, or isometric
-octahedrons; hardness 5.5;
-specific gravity 4.4; color black;
-streak dark-brown; luster submetallic; opaque
-on thin edges.</p>
-<p>In form, color and streak chromite resembles
-magnetite and franklinite. From the magnetite
-it is distinguished by being non-magnetic; from
-the franklinite, by being insoluble in hydrochloric
-acid, while the franklinite is soluble.
-Chromite furnishes practically all the chromium
-used in the arts and manufactures. It is a
-mineral associated with high temperatures, and
-therefore found in dark lavas, serpentine, and
-olivine. It occurs in Pennsylvania, Maryland,
-New Jersey, Montana, Oregon, Wyoming, and
-California.</p>
-<h3 class="center"><span class="sc">Tungsten</span></h3>
-<p>This element is obtained either as a heavy
-dark-gray metal, which is very hard and difficult
-<span class="pb" id="Page_88">88</span>
-to fuse, or as a dark-gray powder. It is used as
-an alloy with iron, one part of tungsten to nine
-of steel, to make the ferrotungsten, which has
-extraordinary hardness, and is used mostly for
-high-speed tools. Tungsten is also one of the
-three metals (cobalt, chromium and tungsten)
-which are alloyed together to make stellite.
-Some of the tungsten supply is also used to
-make the films in incandescent lamps, and in
-some of the chemical industries. It has but one
-important ore, wolframite, and this is found in
-the United States in but small quantities; so
-that we ordinarily have to import the greater
-part of what we use. During the last war, under
-the stimulus of high prices and the urge of necessity,
-we did find and produce substantial quantities
-of tungsten. China is the world&rsquo;s largest
-producer of tungsten ore with Burma second, and
-the United States a poor third.</p>
-<h3><a id="species_Wolframite">Wolframite</a>
-<br />(FeMn)WO&#8324;</h3>
-<p>Occurs in monoclinic crystals or
-in crystalline masses; hardness 5.5;
-specific gravity 7.4; color dark-brown
-to black; streak nearly black; luster
-submetallic; opaque on thin edges.</p>
-<p>If in crystals the form will serve to distinguish
-this mineral from cassiterite and ilmenite, the
-two which it most resembles; but if it is massive
-the only sure way to decide is to put a piece in
-strong sulphuric acid; if it dissolves and throws
-down a yellow precipitate (tungstic acid) it is
-wolframite.</p>
-<div class="pb" id="Page_89">89</div>
-<p>Like the two other minerals mentioned above
-it occurs in veins in igneous rocks, being associated
-with high temperatures. As it is almost
-insoluble in water, like cassiterite and ilmenite,
-it is likely to occur with them in the sands which
-are the result of the disintegration of the rocks
-which carried the minerals; and so a large part
-of the supply today comes from placer deposits.</p>
-<p>It is found in Connecticut, North Carolina,
-Missouri, Colorado, and California.</p>
-<h3 class="center"><span class="sc">Radium, Uranium and Vanadium</span></h3>
-<p>These three metals are all rare and occur
-together. Radium, discovered in 1898, is a
-heavy metal which has proved very useful
-because of its radio-activity, that is, its power of
-giving off or radiating tiny particles of matter
-known as <i>X-rays</i>, part of which are charged with
-positive electricity, and part of them with
-negative electricity. The ability of these rays
-to pass through other substances has made
-possible photographing the denser substances
-within those less dense, as the bones within the
-flesh, or metal within leather or wood, etc.
-The rays have proved of great value medicinally,
-and are also used to make objects luminous in
-the dark. These X-rays are also used in the
-study of the ultimate structure of matter, as it
-can be thus obtained in such small units.</p>
-<p>Uranium is another element which is radio-active
-and can be used for many of the same
-purposes as radium.</p>
-<p>Vanadium, the third of these associated metals,
-<span class="pb" id="Page_90">90</span>
-and the commonest of the group, is not radio-active.
-It is a silvery-white metal, mostly used
-as an alloy with steel to give it great hardness.</p>
-<h3><a id="species_Carnotite">Carnotite</a>
-<br />K&#8322;O&middot;2U&#8322;O&#8323;&middot;V&#8322;O&#8325;&middot;3H&#8322;O
-<br /><a href="#Plate_27">Pl. 27</a></h3>
-<p>Occurs in earthy masses; color yellow.</p>
-<p>This mineral is included here, not
-because it is common, but because
-it is of such great interest. It is the chief source
-of supply in the United States of radium, uranium
-and vanadium. It is a lemon-yellow earth
-or powder, which looks a little like orpiment.
-It is however found in a sandstone, instead of
-where hot waters have deposed minerals. From
-a ton of this ore about 10 pounds of uranium
-oxide, 55 pounds of vanadium and &sup1;/&#8321;&#8320;&#8320;&#8320;th of a
-gram of radium are obtained. Carnotite is found
-in south-west Colorado and south-east Utah, and
-on Carrizo Mountain on the line between Arizona
-and New Mexico.</p>
-<h3 class="center"><span class="sc">Mercury</span></h3>
-<p>Mercury, or quicksilver, is the only metal
-which is liquid at ordinary temperatures. It is
-silvery-white in color, with a striking metallic
-luster, and at the low temperature of 662&deg; F.,
-boils and changes to a colorless vapor. Mercury
-alloys with certain metals, these alloys being
-<span class="pb" id="Page_91">91</span>
-known as amalgams. In this way it is especially
-useful for the recovery of gold and silver, the
-mercury being added to crushed ore, the gold or
-silver uniting with the mercury in a liquid amalgam,
-which is then drawn off and heated to a
-temperature above 662&deg; F., at which temperature
-the mercury volatilizes and is recovered, while
-the gold or silver remains behind. Mercury
-also forms a solid amalgam with tin which is
-used to coat glass, the high metallic luster
-making the most effective looking glass. It is
-also used in medicines (calomel, corrosive sublimate,
-etc.), for scientific instruments (thermometers,
-barometers, etc.), in cosmetics, in
-paints for ship bottoms, etc.</p>
-<p>Though there are some 25 minerals of mercury,
-only one is common or important as a
-source of the metal, cinnabar. The United
-States is self-sufficient as far as mercury is concerned,
-producing just about as much as it
-uses. The leading producers are Spain, Austria,
-Italy, and the United States. Commercially
-mercury is quoted as quicksilver, and in flasks
-of 75 pounds each.</p>
-<h3><a id="species_Cinnabar">Cinnabar</a>
-<br />HgS
-<br /><a href="#Plate_27">Pl. 27</a></h3>
-<p>Occurs in massive or earthy form,
-or in minute crystals in cavities;
-hardness 2.5; specific gravity 8;
-color scarlet to dark red; streak vermilion;
-luster adamantine; translucent on thin edges.</p>
-<p>The bright-red color and the streak are usually
-enough to identify this mineral at once, but some
-of the darker varieties resemble hematite or
-zincite in appearance, but both these have much
-<span class="pb" id="Page_92">92</span>
-greater hardness. When in crystals they are
-tiny hexagonal prisms with pyramids on the end.
-Cinnabar is usually found in or near metamorphic
-or igneous rocks, either in veins leading
-from the igneous rocks, or in metamorphic rocks,
-or it may occur disseminated through metamorphic
-rocks. It is associated with quartz or
-calcite, and may occur with other sulphides
-like pyrite, galena, argentite, etc. It is most
-abundant in California, but is also found in
-Oregon, Washington, Idaho, Arizona, Nevada,
-Utah, Texas, and Montana.</p>
-<h3 class="center"><span class="sc">Tin</span></h3>
-<p>Tin has been known since early Roman times,
-and the mines at Cornwall, England, were worked
-from that time all through down to the present,
-but now they are becoming of minor importance
-as they approach exhaustion. The metal is
-silvery-white, does not easily tarnish, is
-malleable, but has little ductility and little
-tensile strength. Tin is mostly used in making
-tin plate, a thin sheet of steel covered with tin,
-the tin being only 1 to 2% of the total weight.
-This tin plate is mostly made into tin cans, and
-used as containers for food. Some tin is used in
-making solder, tin-foil, tubes for paste, vaseline,
-etc., and around 1000 tons per year for weighting
-silk. This &ldquo;weighting&rdquo; makes the silk heavier
-by about 25% and gives it a &ldquo;rustle,&rdquo; which,
-while much in evidence, is really indicative that
-the silk is not pure. The United States produces
-very little tin, most of the world&rsquo;s supply coming
-<span class="pb" id="Page_93">93</span>
-from the Malay Peninsula, Dutch East Indies,
-China, and Bolivia, with small amounts from
-several other countries.</p>
-<h3><a id="species_Cassiterite">Cassiterite</a>
-<br />SnO&#8322;
-<br /><a href="#Plate_28">Pl. 28</a>
-<br /><i>tin stone</i></h3>
-<p>Occurs in tetragonal crystals,
-massive, or in grains and pebbles;
-hardness 6.5; specific gravity 7;
-color black or dark-brown; streak gray; luster
-adamantine; translucent on thin edges.</p>
-<p>The crystals are short prisms with pyramidal
-ends. Twinning is common. Cassiterite also
-occurs in fibrous masses, and when it is weathered
-from its original location, is so insoluble and
-hard, that it remains as grains and pebbles,
-making placer-deposits, from which today three
-quarters of the supply is obtained. If pure, the
-crystals would be colorless, but impurities of
-iron and titanium give it the dark-brown to
-black color. Cassiterite may appear very like
-rutile, the crystalline forms being identical, but
-the reddish tinge of color in the rutile will
-separate the two.</p>
-<p>Cassiterite is one of those minerals which result
-from deposition at very high temperatures,
-probably from vapors, and is found in the veins
-in igneous rocks, such as light-colored granites,
-gneisses, syenites, etc. While not mined in this
-country it is found in small quantities in Maine,
-Massachusetts, New Hampshire, Virginia, Alabama,
-Wyoming, Montana, and California.</p>
-<h3 class="center"><span class="sc">Titanium</span></h3>
-<p>Titanium, as a metal, is a heavy, gray, iron-like
-powder, which is chiefly useful as an alloy
-<span class="pb" id="Page_94">94</span>
-with iron, giving it toughness, and preventing
-bubbles and cracks in casting. It is not as rare as
-some other metals which have found a wider use.</p>
-<h3><a id="species_Rutile">Rutile</a>
-<br />TiO&#8322;
-<br /><a href="#Plate_28">Pl. 28</a></h3>
-<p>Occurs in tetragonal crystals,
-and in grains; hardness 6.5; specific
-gravity 4.2; color red to reddish-brown;
-streak yellowish-brown; luster metallic
-to adamantine; translucent on thin edges.</p>
-<p>Rutile usually occurs in crystals, which are
-either short and stout, or in needle-like crystals.
-Twinning is common. In form and general
-appearance it resembles cassiterite, but the
-reddish color, and the yellowish-brown streak
-will distinguish the rutile. It is found in similar
-rocks, granites, gneisses, syenites, and mica-schists,
-the two minerals cassiterite and rutile
-often occurring together. This is also true of the
-grains, which have been weathered out and are
-found in sands and gravels of placer deposits.
-It is found in small quantities in all the New
-England States, New York, and all down the
-Appalachian Mountains, especially at Graves
-Mountain, Ga., and in Arkansas and Alaska.</p>
-<h3><a id="species_Ilmenite">Ilmenite</a>
-<br />FeTiO&#8323;</h3>
-<p>Occurs in granular masses, as
-black sand, or as tabular hexagonal
-crystals; hardness 5-6; specific gravity
-4.7; color black; streak brownish-red to
-black; luster metallic; opaque on thin edges.</p>
-<p>When ilmenite occurs in crystals they are
-tabular and resemble hematite in its darker
-varieties, but the streak readily distinguishes the
-two. In masses it looks like magnetite, but the
-lack of magnetism serves to distinguish these
-<span class="pb" id="Page_95">95</span>
-two minerals. It is very likely to be associated
-with cassiterite, rutile, or magnetite in grains
-which have weathered out of the original rock,
-and have resisted solution and wear. Sands with
-a large amount of the above mentioned minerals
-are termed &ldquo;black sands,&rdquo; some of which are
-important for one or another of these minerals.</p>
-<p>Ilmenite is a mineral formed at high temperatures,
-and probably often deposited from hot
-vapors. It is found in granites, syenites, and
-gneisses. Among the better known localities
-are Orange, N. Y., Litchfield, Conn., Florida,
-California, etc.</p>
-<h3 class="center"><span class="sc">Platinum</span></h3>
-<p>This metal is steel-gray in color, very malleable
-and ductile, almost infusible and resists the
-action of acids. It is one of the &ldquo;noble&rdquo; metals,
-much rarer than gold, and so has become popular
-for jewelry. It is also used in the manufacture
-of sulphuric-acid, in nitrogen-fixation plants, for
-chemical utensils, in the electrical industries, and
-in dentistry. Platinum in its occurrence is
-associated with the certain other equally rare
-elements, like iridium, palladium and osmium.
-Its use has increased rapidly of late, but the
-supply has not kept up with the demand, so
-that, whereas in 1906 platinum and gold were
-about equally valuable, now the platinum brings
-about five times as much as the gold.</p>
-<h3><a id="species_Platinum">Platinum</a>
-<br />Pt</h3>
-<p>Occurs in grains or nuggets;
-hardness 4.5; specific gravity 19
-(21 if pure); color steel-gray; luster
-metallic; opaque.</p>
-<div class="pb" id="Page_96">96</div>
-<p>This rare metal is mostly found in placer-deposits,
-often with gold. It comes originally
-from dark igneous rocks, like peridotite, pyroxenite,
-etc., and platinum is found to be associated
-with the nickel ores of Sudbury, Canada. While
-formerly 90% of the world&rsquo;s supply of platinum
-came from placer mines in the Ural Mountains,
-today more than half is produced in Canada and
-about a fifth in Russia. In the United States it
-is found in California, Oregon, Nevada, and
-Alaska.</p>
-<h3 class="center"><span class="sc">The Magnesium Group</span></h3>
-<p>Magnesium is a silvery-white metal, easily
-tarnished by exposure to moist air. Because of
-its light weight, less than twice the weight of
-water, and strength, it is being substituted for
-aluminum, especially in airplanes, where the
-question of weight is crucial. It is also used in
-automobile and ship production and other machine
-industries, and in the manufacture of flares
-and incendiary bombs. Magnesium is obtained
-chiefly from magnesite, dolomite, and in the
-United States as a result of a recently developed
-process, from sea water. Magnesium has a
-<span class="pb" id="Page_97">97</span>
-considerable number of minerals, of which three
-are taken up here and several more under the
-head of silicates, where both magnesium and
-silicon are combined in a mineral.</p>
-<h3><a id="species_Spinel">Spinel</a>
-<br />MgAlO&#8324;
-<br /><a href="#Plate_29">Pl. 29</a></h3>
-<p>Occurs mostly as isometric octahedrons;
-hardness 8; specific gravity
-3.5; color, red, yellow, green, or
-black; streak white; luster vitreous; transparent
-on thin edges.</p>
-<p>This is a rather rare mineral, but, when in
-clear crystals is considered one of the gems. It
-was early confused with corundum, and the red
-variety called ruby, as it was found in the same
-gem-bearing sands in Ceylon, Burma, and Siam.
-However the form of the isometric octahedron
-as compared with the hexagonal prism of the
-corundum, together with the lesser hardness
-are sufficient to distinguish the two easily.
-The crystals are usually octahedrons, but may
-have the corners cut or the edges beveled.
-Twins are not uncommon.</p>
-<p>The standard color is a clear deep-red, and
-such a spinel is known in the gem trade as a
-<i>spinel-ruby</i>. If the color is rose-red, it is a
-<i>Balas ruby</i>; if orange, it is <i>rubicelle</i>, if of a violet
-tinge, <i>almandine</i>. When small quantities of
-other elements replace the magnesium, the color
-is greatly changed. For example a little iron
-present gives the crystals a dark-green to black
-color, and the spinel is known as <i>ceylonite</i>. If
-there is both iron and chromium present, the
-color becomes yellowish or greenish-brown, and
-this variety is <i>picotite</i>. When the impurities
-<span class="pb" id="Page_98">98</span>
-are iron and copper, the color becomes grass-green,
-and it is called <i>chlorospinel</i>. A form, in
-which the magnesium is completely replaced by
-iron, is black in color and termed <i>hercynite</i>, and
-occurs fairly abundantly in Westchester Co.,
-N. Y. From Amity, N. Y., to Andover, N. J.,
-there is a belt of granular limestone in which
-spinel of all colors is found. St. Lawrence Co.,
-N. Y., is also a rich locality. Bolton, Mass.,
-Newton, Sterling, and Sparta, N. J., North
-Carolina, Alabama, and California all yield
-spinel.</p>
-<h3><a id="species_Magnesite">Magnesite</a>
-<br />MgCO&#8323;</h3>
-<p>Occurs in cleavable or compact
-porcelain-like masses; hardness 4;
-specific gravity 3.1; color white to
-gray; luster vitreous; translucent on thin
-edges.</p>
-<p>Magnesite is white and brittle, and cleaves
-perfectly parallel to the faces of the rhombohedron,
-but it seldom occurs in crystals. It will
-effervesce in warm hydrochloric acid and has
-some resemblance to calcite, but can be distinguished
-by the greater hardness. It is still
-more like dolomite, both having the same color
-and cleavage, both effervescing in warm hydrochloric
-acid; but the magnesite has half a point
-greater hardness and the porcelainous appearance.
-Magnesite is used in toilet preparations,
-paper making, and mixed with asbestos, as a
-covering for heating pipes.</p>
-<p>Magnesite is found in Massachusetts, Pennsylvania,
-Texas, and in large deposits in California
-and Washington.</p>
-<div class="pb" id="Page_99">99</div>
-<h3><a id="species_Dolomite">Dolomite</a>
-<br />(MgCa)CO&#8323;
-<br />Pl. <a href="#Plate_19">19</a> &amp; <a href="#Plate_29">29</a></h3>
-<p>Occurs in crystals, or in cleavable
-or granular masses; hardness 3.5;
-specific gravity 2.8; color white to
-pink or gray; streak white; luster vitreous;
-transparent on thin edges.</p>
-<p>Dolomite crystallizes in the hexagonal system,
-in rhombohedrons (hemihedral form), which are
-more or less modified by faces on the corners or
-edges. The cleavage is parallel to the rhombohedron,
-and it will effervesce in warm hydrochloric
-acid. Sometimes the crystal faces are
-curved, and when this is the case, dolomite is
-easily determined. Usually however dolomite
-resembles both calcite and magnesite. From the
-calcite it is distinguished by the greater hardness,
-and from magnesite by lesser hardness and not
-being porcelainous in appearance. Some of the
-commoner forms are shown on <a href="#Plate_29">Plate 29</a>, crystals
-like C being found embedded in anhydrite and
-gypsum.</p>
-<p>Magnesium is a common element and is likely
-to be present wherever lime is being deposited,
-so dolomite crystals are common, and much of
-the limestone is dolomitic.</p>
-<p>It may be found in almost any limestone
-section of the country. Some of the finest
-crystals of dolomite however come from Roxbury,
-Vt., Smithfield, R. I., Hoboken, N. J.,
-Lockport, Rochester, and Niagara Falls, N. Y.,
-etc.</p>
-<h3 class="center"><span class="sc">Silicon, Silica and the Silicates</span></h3>
-<p>Silicon is one of the non-metallic elements, and
-does not occur as such in Nature. When isolated
-<span class="pb" id="Page_100">100</span>
-it is either a dark-brown powder, or steel-gray
-crystals. However silicon is next to oxygen in
-its importance in making the crust of the earth.
-Forty-seven per cent of the surface rocks are
-composed of oxygen, and 28% of silicon, the
-latter appearing in a host of minerals. The
-oxide of silicon is termed silica (SiO&#8322;), its crystal
-form being quartz, the commonest of all minerals.
-In non-crystalline form silica is also widely distributed,
-as chalcedony and opal, even appearing
-in the tissues of animals and plants, as in the
-feathers of birds, the shells of certain Protozoa
-(Radiolaria), the spicules of sponges; and in
-plants, as the shells of diatoms, and in the stalks
-of grasses, especially cereals and bamboo. Silica
-in the form of sand is widely used in making
-glass, porcelain, china, etc., and in the various
-cements.</p>
-<p>Then there are a considerable number of acids
-of silicon, which do not occur in Nature, but their
-salts do, and make a host of minerals, which are
-known as the silicates, such as mica, feldspar,
-hornblende, etc. Either as quartz, or as
-silicates, silicon is represented in most all the
-igneous and metamorphic rocks and in many of
-the sedimentary rocks.</p>
-<h3><a id="species_Quartz">Quartz</a>
-<br />SiO&#8322;
-<br /><a href="#Plate_30">Pl. 30</a></h3>
-<p>Occurs as hexagonal crystals, or
-in grains or masses; hardness 7;
-specific gravity 2.65; colorless when
-pure; luster vitreous; transparent on thin edges.</p>
-<p>Quartz is not hard to identify. Its hardness
-and the crystal-form separate it from most all
-other minerals. It is the most common mineral,
-<span class="pb" id="Page_101">101</span>
-making 12% of the earth&rsquo;s crust. The usual
-crystal form is a hexagonal prism with the sides
-horizontally striated, and a six-sided pyramid on
-one or both ends. This six-sided pyramid is
-really two rhombohedrons, a right-handed one
-and a left-handed one, so that the alternate
-faces of the pyramid may show peculiarities, for
-instance three may be large and three small, as
-in Fig. B, <a href="#Plate_30">Plate 30</a>, or the alternate ones may be
-duller or etched in some manner. The crystals
-are clear and when pure colorless, but there is a
-tendency for some slight impurity to color them
-almost any hue.</p>
-<p>The most perfect double-ended crystals form
-only where growth is possible in all directions,
-as in clay. In cavities and caves there is an
-opportunity for the crystals to grow in toward
-the open spaces, and in such places, one finds
-fine large crystals; the Alps, Brazil, Japan, and
-Madagascar being especially famous localities.
-The largest quartz crystal on record is one 25
-feet in circumference which came from Madagascar.
-In this country the caves at Little Rock,
-Ark., have furnished some very fine large crystals.
-Smaller, but very clear crystals, come from about
-Herkimer, N. Y. Some of these have been used
-as &ldquo;Rhine-stones&rdquo; and as cheap imitations of
-diamonds. Clear quartz is beautiful enough to
-be a gem, but it is too common to interest people
-as jewelry, however many objects of art have
-been carved from it. One of these took the form
-of crystal balls, which, through the Middle
-Ages particularly, developed into a form of
-mysticism. The gazing into the crystal ball was
-<span class="pb" id="Page_102">102</span>
-supposed to give some people supernatural
-vision. It seems to be a form of hypnotism,
-gazing at the bright reflecting surface tiring the
-eye, and making possible visions, which are
-subjective rather than anything external.</p>
-<p>Silica is slightly soluble in water, especially
-when it is alkaline; so that most river-, lake-, and
-sea-waters have some silica in solution, and are
-carrying it from one place to another. The
-waters, which percolate through the rocks, carry
-even more, and when they come out into open
-spaces, they give up some of the silica, making
-crystals lining these openings, whether fissures or
-cavities. Not infrequently these silica-bearing
-waters dissolve out some other crystal, and then
-deposit in its place silica, thus making a crystal
-which has the form of what was dissolved, rather
-than that of quartz. Such a form is known as a
-pseudomorph.</p>
-<p>When molten masses of igneous rock were
-cooling the quartz crystals had their faces interfered
-with as they grew, and we have resulting
-crystalline quartz, simply filling in the spaces
-between the other crystals, such as feldspar and
-mica, in the granite. Quartz is a large component
-in many igneous rocks, also in metamorphic
-rocks, and certain sedimentary rocks
-like sandstone are almost wholly made up of
-quartz grains. Quartz is also the gangue mineral
-in many veins. In this case it seems to have been
-deposited from hot water or vapors, as they rose
-from cooling magmas. With it are associated
-all sorts of metallic ores as has been suggested.</p>
-<p>Quartz has been largely used to make imitations
-<span class="pb" id="Page_103">103</span>
-of other much rarer minerals, sometimes
-in its crystalline form to imitate the diamond,
-at other times ground and made into a &ldquo;paste,&rdquo;
-which is colored to imitate other gems. This
-paste is a mixture of about 4 parts of quartz,
-5 parts of red lead and 1 part of potassium carbonate,
-melted and cooled slowly. It is clear and
-has a brilliant luster like the diamond. If some
-coloring matter is put into it it can be used for
-rubies, sapphires, etc. When there is any reason
-to think that this is being used, it is easily
-detected by being so much softer than any of the
-true gems, and even than true quartz. Quartz
-will scratch glass readily, but this imitation has
-only the hardness of very soft glass, or about 5.</p>
-<h3 class="center"><span class="sc">Varieties of Quartz</span></h3>
-<p><b>Rock crystal</b> is the term applied to quartz when
-it is clear and colorless.</p>
-<p><b>Milky quartz</b> is the milky variety, the whiteness
-being due to imperfections in the crystallization,
-such as cracks, bubbles, etc.</p>
-<p><b><a id="species_SmokyQuartz">Smoky quartz</a></b> is the cloudy brown-colored
-variety, which results from the presence of small
-quantities of organic matter (hydrocarbons) in
-the quartz. If the color is so dark as to be almost
-black it is termed <b>morion</b>. In the above cases
-the color will disappear if the stone is heated.
-Pebbles of smoky quartz from Cairngorm, Scotland,
-have been so widely used as semiprecious
-stones that they have come to be known as
-<b>cairngorms</b>.</p>
-<p><b>Citrine</b>, or <b>false topaz</b>, is a clear yellow variety,
-the color again due to the presence of organic
-<span class="pb" id="Page_104">104</span>
-matter. It is distinguished from true topaz by
-the lesser hardness, this having the hardness of
-7, while true topaz has a hardness of 8.</p>
-<p><b><a id="species_Amethyst">Amethyst</a></b> is quartz with a violet color, due to
-the presence of small quantities of manganese.
-To be suitable for cutting into gems, the color
-must be deep or the small pieces will appear almost
-colorless. It is widely used today as a
-semiprecious stone in jewelry; and in the fifteenth
-century it had the traditional virtue of making the
-wearer sober-minded, whether he had taken too
-freely of wine, or was over excited by love-passion.</p>
-<p><b><a id="species_RoseQuartz">Rose quartz</a></b> gets its pale-red color from the
-presence of a small amount of titanium. It is
-widely distributed, but is more abundant in the
-Black Hills of South Dakota.</p>
-<p><b>Aventurine</b> is quartz which has inclosed tiny
-scales of mica or hematite giving it a spangled
-appearance.</p>
-<p><b><a id="species_Prase">Prase</a></b> is a green quartz, the color being due to the
-inclusion of fibrous crystals of green actinolite.</p>
-<p><b>Cat&rsquo;s Eye</b> is a quartz which has inclosed silky
-fibers of asbestos. When this is cut parallel to
-the fibers, the effect is opalescent. The colors
-are greenish, yellowish-gray, and brown. This
-form, however, is not to be confused with the
-true or Oriental Cat&rsquo;s Eye, which is chrysoberyl
-and has the hardness of 8.</p>
-<h3><a id="species_Chalcedony">Chalcedony</a>
-<br />SiO&#8322;</h3>
-<p>Non-crystalline, occurring in botryoidal,
-stalactitic or concretionary
-masses; hardness, 7; specific gravity,
-2.65; color white when pure; luster waxy; translucent
-to transparent on thin edges.</p>
-<div class="pb" id="Page_105">105</div>
-<p>In addition to the crystalline form, silica is
-freely deposited in an amorphous or cryptocrystalline
-form which has the same properties as
-quartz, except the crystal faces. This is called
-chalcedony, and it occurs in seams, cavities and
-free surfaces. When the surface of a chalcedony
-deposit is free it has a waxy luster. It is generally
-very brittle and breaks in a peculiar splintery
-manner. Like quartz it also has a great
-many varieties, according to the impurities present.
-Its wide distribution, hardness, and the
-manner in which it can be chipped have made
-this a most important stone in the history of the
-development of civilization. The early men first
-broke it into rough tools, such as knives, axes,
-spear points, etc., and used these as cutting tools,
-of one sort or another, because they held their
-edge better than most stones. We apply, to the
-people who used only these chipped stones as
-tools, the term &ldquo;<i>Men of the Old Stone Age</i>,&rdquo; or the
-period is termed the <i>Pal&aelig;olithic Age</i>. Later men
-learned how to grind the edge to a smoother
-outline, and this much shorter period is termed
-the <i>Neolithic Age</i>. The use of flints for the first
-tools is world-wide, and the American Indian
-when discovered was still using chalcedony in its
-rough-hewn state.</p>
-<div class="verse">
-<p class="t2">&ldquo;There the ancient Arrow-maker</p>
-<p class="t0">Made his arrow heads of sandstone,</p>
-<p class="t0">Arrow heads of chalcedony,</p>
-<p class="t0">Arrow heads of flint and jasper,</p>
-<p class="t0">Smoothed and sharpened at the edges,</p>
-<p class="t0">Hard and polished, keen and costly.&rdquo;</p>
-</div>
-<div class="pb" id="Page_106">106</div>
-<p><b>Chalcedony</b> is the proper term to use when the
-color is white to translucent, in which case the
-surfaces are usually botryoidal and waxy.</p>
-<p><b><a id="species_Carnelian">Carnelian</a></b> is chalcedony which is clear red in
-color and translucent. This is one of the first
-stones used for ornamental purposes and for engraving.
-Carnelians with figures engraved on
-them were used by the Egyptians, Assyrians
-and The Children of Israel, at least 2000 <span class="small">B.C.</span>;
-and the Egyptian scarabs of the fifth or sixth
-century <span class="small">B.C.</span>, were often carved from this variety
-of chalcedony, as well as from jasper and agates.</p>
-<p>The brownish varieties are termed <i>sard</i>.</p>
-<p><b><a id="species_Chrysoprase">Chrysoprase</a></b> is an apple-green variety of
-chalcedony the color being due to the presence
-of nickel oxide. This is by no means as common
-as most of the varieties of chalcedony, and was
-long prized as a gem.</p>
-<p><b><a id="species_Plasma">Plasma</a></b> is chalcedony with a leek- to emerald-green
-color, and the same stone when it has small
-red spots of jasper in it is termed <i>blood-stone</i>,
-or <i>heliotrope</i>. These red spots are said by tradition
-to be drops of the blood of Christ.</p>
-<p><b><a id="species_Jasper">Jasper</a></b> is a deep red chalcedony, the color being
-due to hematite, which is so abundant as to make
-it opaque. A brown variety colored by limonite
-is also called jasper, and even green jaspers are
-found. In all cases the opaque character is
-common.</p>
-<p><b><a id="species_Flint">Flint</a></b> is an impure brown chalcedony, usually
-forming concretions. The color is due to organic
-matter. Flint is mostly found in limestone or
-chalk, and the concretions are the result of the
-small particles of silica scattered through the
-<span class="pb" id="Page_107">107</span>
-rock being dissolved, and then reprecipitated
-about some organic center. Generally the silica
-was obtained by the dissolution of small fossils,
-like the shells of diatoms or sponge spicules.</p>
-<p><b><a id="species_Hornstone">Hornstone</a></b> and <b><a id="species_Chert">Chert</a></b> are simply impure varieties
-of flint, brown in color, and with a splintery
-fracture.</p>
-<p><b><a id="species_Agate">Agate</a></b>, <a href="#Plate_32">Plate 32</a>, is a banded or cloudy chalcedony
-which has formed in a cavity, the layers of
-different color representing deposition from
-water, carrying first silica with one impurity,
-then later, silica with another impurity. Gradually
-the cavity has been thus filled with silica;
-and when the mass is freed by the weathering
-away of the surrounding rock, these banded
-masses are found. Sometimes the manner of
-deposition has changed, and while the outer part
-of the cavity was filled with chalcedony, the
-central part will contain quartz crystals. On
-account of the beauty of the colors, and the unusual
-way in which they may be developed,
-agates are widely used for semiprecious jewelry
-and objects of art, and this has been true since
-ancient times, the name itself coming from the
-River Achates in Sicily. The center for cutting
-and polishing agates is at Oberstein, Germany,
-where this work has been carried on since the
-middle of the fifteenth century. In spite of the
-many fine natural colors in agates, they are sometimes
-artificially colored, in many cases by methods
-which are kept as &ldquo;trade secrets.&rdquo; The
-color seldom penetrates far; so that even slight
-chipping reveals whether an inferior agate has
-been taken and colored up, or whether the stone
-<span class="pb" id="Page_108">108</span>
-is natural. Moss agates are chalcedony which
-has inclosed dendritic masses of some one of the
-manganese compounds as shown under manganite,
-<a href="#Page_73">p. 73</a>.</p>
-<p><b><a id="species_Onyx">Onyx</a></b> is a variety of agate where the bands are
-alternately black and white; while <b>sardonyx</b> is
-agate with red or brown bands alternating with
-the white. Such agates as these are especially
-desirable for cameo work, where the figure is
-carved in the chalcedony of one color, and the
-other color makes the background.</p>
-<p><b>Silicified</b> or <i>agatized wood</i> is a form of chalcedony,
-where silica has replaced wood, molecule
-by molecule; so that in good specimens, all the
-structure of the wood is still retained, and when
-thin sections are made it can be studied under
-the microscope almost as well as modern wood.
-This takes place under water, usually, if not always,
-in fresh water. Such fossilized wood is
-widely distributed in the western United States,
-the most famous cases being the Fossil Forest of
-Arizona, now a National Reservation, and the
-fossil trees in the Yellowstone National Park.</p>
-<h3><a id="species_Opal">Opal</a>
-<br />SiO&#8322;&middot;H&#8322;O
-<br /><a href="#Plate_33">Pl. 33</a></h3>
-<p>Non-crystalline, massive, stalactitic
-or nodular; hardness, 6; specific
-gravity 2; all colors; luster vitreous,
-resinous, or pearly; transparent on thin
-edges.</p>
-<p>Opal differs from chalcedony in having water,
-usually about 10%, incorporated in its structure.
-This is water of crystallization, and not firmly
-held; so that, if opal is heated in a closed tube to
-above 100 C., it is given off as a vapor. Opal is
-<span class="pb" id="Page_109">109</span>
-distinguished from chalcedony by its lesser hardness,
-and the resinous to pearly luster. It forms
-in cavities, in layers often of extreme thinness.</p>
-<p>Opal is originally the product of the dissolution
-of silicate minerals in hot acid waters, the resulting
-gelatinous silica, when it is deposited and
-hardened, becoming the opal. There are many
-varieties, some of them highly prized as gems in
-spite of the moderate hardness and opacity of
-the mineral. Gem-quality opal gets its opalescent
-character from the successive deposition
-of thin films of opal, the light penetrating and
-being reflected from different films. This breaks
-up the white light and causes the play of colors
-which is the charm of this gem.</p>
-<p><b>Precious opal</b>, in which the play of colors is
-finest, comes mostly from Hungary, Mexico, and
-Queensland. The opal was a favorite stone from
-before Roman times, and in its early history was
-a charm against the &ldquo;evil eye.&rdquo; During the
-nineteenth century for some reason it came to be
-considered an unlucky stone.</p>
-<p><b><a id="species_FireOpal">Fire opal</a></b> is a hyacinth-red to honey-yellow
-variety, which has a fire-like play of color, and
-is found in Mexico and Honduras.</p>
-<p><b>Common opal</b> does not have the play of color,
-but comes in a variety of colors; is waxy or greasy
-in luster; and occurs mostly as fillings of seams or
-cavities, especially those in igneous rocks, like
-the steam holes in lavas, etc. It is found in
-Cornwall, Penn., in Colorado, California, etc.</p>
-<p><b>Opal-agate</b> is a variety in which there are
-color bands, and it is widely distributed.</p>
-<p><b>Opalized wood</b> is formed in exactly the same
-<span class="pb" id="Page_110">110</span>
-manner as agatized wood, much of the fossil wood
-called silicified being really opalized.</p>
-<p><b>Siliceous sinter</b> is the porous mass of opal
-which is so frequently deposited about hot
-springs and geysers. It is readily recognized by
-its porous character.</p>
-<p>The shells of the diatoms, which are microscopic
-plants, are made of opal; and while they
-are so small, there is certainly no other plant so
-abundant or omnipresent, living as it does in
-every pool, lake, or sea by the millions. These
-shells are very indestructible so that they
-accumulate at the bottom of ponds, bogs, and
-sea-bottoms, making at times extensive deposits.
-This material in quantities is termed diatomaceous
-earth, or <b>tripolite</b> (from Tripoli where it was
-first used commercially). It is used as a polishing
-powder for metals, marble, glasses, etc.</p>
-<h3 class="center"><span id="species_Feldspar" class="sc">The Feldspars</span></h3>
-<p>The term feldspar is a family name for a large
-variety of very common minerals, which altogether
-make up nearly 60% of the crust of the
-earth, being the predominant part of granites,
-gneisses, and lavas. In composition they are
-silicates of aluminum, together with potassium,
-sodium and calcium, and their mixtures. They
-may be tabulated as follows:</p>
-<dl class="undent"><dt>1. KAlSi&#8323;O&#8328;, <i>orthoclase</i>, the silicate of aluminum and potassium.</dt>
-<dt>2. NaAlSi&#8323;O&#8328;, <i>albite</i>, the silicate of aluminum and sodium.</dt>
-<dt>3. CaAlSi&#8322;O&#8328;, <i>anorthite</i>, the silicate of aluminum and calcium.</dt>
-<dt>4. Mixtures of 1 and 2 are <i>alkalic feldspar</i>.</dt>
-<dt>5. Mixtures of 2 and 3 are <i>plagioclase feldspar</i>.</dt></dl>
-<div class="pb" id="Page_111">111</div>
-<p>Orthoclase is monoclinic, but the rest of the
-feldspars are triclinic. If crystals are available
-they may be short and stout, or tabular and thin,
-but as the feldspars are mostly components of the
-igneous rocks, where perfect crystals have not
-had a chance to grow, they are mostly determined
-by their hardness and cleavage. The hardness
-of all the feldspars is 6 or very close to it.</p>
-<p>They all have three planes of cleavage, two of
-which are good and intersect either at 90&deg; as in
-orthoclase, or at about 86&deg; as in the plagioclase
-series; while the third cleavage plane is imperfect.
-In figure 1, <a href="#Plate_34">Plate 34</a>, a and b are the two perfect
-cleavages, while c is the imperfect one. Breaking
-into such cleavage masses as the one illustrated
-is characteristic of feldspar. The specific gravity
-ranges from 2.55 to 2.75. The luster is vitreous,
-and the color white, ranging to various shades
-of gray and pink, and, sometimes in recent lavas,
-colorless.</p>
-<p>Twinning is very common and helps to distinguish
-orthoclase from the plagioclase feldspars.
-In orthoclase the twins are simple, that is, only
-two crystals growing together, and are united
-on one of the faces, as if one of them had been
-revolved 180&deg; with the other; or, while related to
-each other as in the preceding case, they may
-seem to grow through each other. On <a href="#Plate_34">plate 34</a>
-are three orthoclase crystals showing this simple
-type of twinning. The first (A) is a simple crystal;
-the second (B) shows the simplest type of twinning
-where the left-hand crystal has revolved
-<span class="pb" id="Page_112">112</span>
-180&deg; on the p face, and the end is composed, half
-of the upper end of one crystal, and half of the
-lower end of the adjacent crystal. The presence
-of re&euml;ntrant angles calls attention to the twinning.
-The third figure (C) is a case of intergrowing
-crystals.</p>
-<p>In the plagioclase feldspars twinning is multiple,
-a large number of crystals, each thin,
-sometimes as thin as paper, growing side by side,
-the first one in normal position, the next at 180&deg;
-with it, the third revolved 180&deg; to the second and
-thus parallel to the first, and so on. The result
-is first of all a striated appearance, and second
-that, as plagioclase crystals have their prism
-faces intersecting at 86&deg;, there is a series of low
-roofs and valleys, which are best seen by holding
-the piece of feldspar so the light reflects from a
-cleavage face, when it will appear striated; then
-by tilting it about 8 degrees a second set of reflections,
-also appearing striated, will appear.
-The light was first reflected from one side of the
-roofs, and in the second case from the other
-side. Figure D, <a href="#Plate_34">Pl. 34</a>, is a diagram showing the
-relation of the individual crystals in a multiple
-twinned piece of plagioclase, in which the crystals
-are represented as rather large. <a href="#Plate_35">Plate 35</a>,
-under labradorite, shows a photograph of a cleavage
-piece, on which is readily seen the striation
-which is characteristic of the plagioclase feldspars.</p>
-<p>Mixtures of albite and anorthite occur in bewildering
-numbers, one or the other predominating,
-and each mixture being uniform throughout
-the crystal and in the whole mass; so each combination
-is a mineral, each with its special properties;
-<span class="pb" id="Page_113">113</span>
-but the different plagioclase feldspars are
-so similar in appearance, that by the naked eye
-it is impossible to separate the closely related
-ones. This can be done under the microscope by
-studying the angles at which light is cut off, and
-also by chemical analyses. For our purposes six
-types will suffice to illustrate the group, and their
-composition may be indicated as follows.</p>
-<p>Albite is albite with up to 15% of anorthite
-mixed with it.</p>
-<p>Oligoclase is albite with from 15-25% of
-anorthite mixed with it.</p>
-<p>Andesite is albite with from 25-50% of anorthite
-mixed with it.</p>
-<p>Labradorite is anorthite with from 25-50%
-of albite mixed with it.</p>
-<p>Bytownite is anorthite with from 15-25% of
-albite mixed with it.</p>
-<p>Anorthite is anorthite with up to 15% of
-albite mixed with it.</p>
-<p>The best method for distinguishing these
-feldspars of the plagioclase group is to measure
-the angle between the two perfect cleavage faces,
-and even this requires careful measurement. The
-angles between these faces are as follows:</p>
-<table class="center" summary="">
-<tr><td class="l">Orthoclase </td><td class="l">90&deg;</td></tr>
-<tr><td class="l">Microcline </td><td class="l">89&deg; 30&prime;</td></tr>
-<tr><td class="l">Oligoclase </td><td class="l">86&deg; 32&prime;</td></tr>
-<tr><td class="l">Andesite </td><td class="l">86&deg; 14&prime;</td></tr>
-<tr><td class="l">Labradorite </td><td class="l">86&deg; 14&prime;</td></tr>
-<tr><td class="l">Bytownite </td><td class="l">86&deg; 14&prime;</td></tr>
-<tr><td class="l">Anorthite </td><td class="l">86&deg; 50&prime;</td></tr>
-</table>
-<h3><a id="species_Orthoclase">Orthoclase</a>
-<br />KAlSi&#8323;O&#8328;</h3>
-<p>Occurs in granites, syenites,
-gneisses and light-colored lavas;
-hardness, 6; specific gravity, 2.57;
-color white to gray or pink; cleavage in two directions
-<span class="pb" id="Page_114">114</span>
-perfect and at 90&deg;, in the third direction
-imperfect; luster vitreous; translucent on thin
-edges.</p>
-<p>Orthoclase is monoclinic, and when formed in
-cavities develops as crystals, but it is usually a
-constituent of igneous rocks, in which case the
-crystals have not had the opportunity to develop
-the crystal faces, and the orthoclase is in grains
-or irregular masses; and the best way of determining
-the mineral is the cleavage, the two
-perfect cleavage planes intersecting at right
-angles. Twinning is frequent but of the simple
-type, only two crystals being united, similar to
-either B or C on <a href="#Plate_34">plate 34</a>.</p>
-<p>It is found in granites, gneisses or lavas, wherever
-they occur, being especially characteristic
-of the granites of the Rocky Mountains.</p>
-<h3><a id="species_Microcline">Microcline</a>
-<br />KAlSi&#8323;O&#8328;
-<br /><a href="#Plate_35">Pl. 35</a></h3>
-<p>Occurs in granites and gneisses
-as crystals or irregular masses; hardness,
-6; specific gravity, 2.56; color
-white to gray, pink, or greenish; luster vitreous;
-translucent on thin edges.</p>
-<p>Microcline has the same composition as orthoclase,
-but is in the triclinic system, the c axis
-being inclined a half degree away from a right
-angle with the b axis. This is best seen in the
-cleavage pieces, the two perfect cleavage planes
-meeting at 89&deg; 30&prime;, and this is the only test for
-determining this mineral by the unaided eye.
-Pike&rsquo;s Peak is the best known locality for microcline,
-and there it occurs in fine large crystals
-of greenish color, which are known as <i>Amazon
-stone</i>.</p>
-<div class="pb" id="Page_115">115</div>
-<h3><a id="species_Albite">Albite</a>
-<br />NaAlSi&#8323;O&#8328;</h3>
-<p>Occurs in small crystals, or more
-often in lamellar masses in granites
-or in seams in metamorphic rocks;
-hardness, 6; specific gravity, 2.62; color white to
-gray; luster vitreous.</p>
-<p>Albite may occur in simple crystals, in which
-case the two perfect cleavage planes meet at an
-angle of 86&deg; 24&prime;. However, it is much more
-frequently found twinned in the multiple manner,
-the individual crystals often being as thin as
-paper. This gives rise to a fine striation on the
-end of a crystal, or on the surface made by the
-imperfect cleavage plane. Where the crystals
-are extremely thin, the surface may have a pearly
-luster. Albite types of granite often inclose
-secondary minerals, that are prized as gems, such
-as topaz, tourmaline, and beryl.</p>
-<p>It is found at Paris, Me., Chesterfield, Mass.,
-Acworth, N. H., Essex Co., N. Y., Unionville,
-Penn., and in Virginia, and throughout the
-Rocky Mountains.</p>
-<h3><a id="species_Oligoclase">Oligoclase</a>
-<br />(NaCa)AlSi&#8323;O&#8328;</h3>
-<p>Generally found in cleavable
-masses in granites and lavas, rarely
-in crystals; hardness, 6; specific
-gravity, 2.65; color white, greenish or pink; luster
-vitreous; translucent on thin edges.</p>
-<p>Oligoclase is a plagioclase feldspar and is distinguished
-by its two perfect cleavage planes
-meeting at an angle of 86&deg; 32&prime;, but otherwise it is
-very like albite. Crystals are not common, and
-it occurs mostly in masses, making one of the
-components of granite or lava.</p>
-<p>It is found in St. Lawrence Co., N. Y., Danbury
-<span class="pb" id="Page_116">116</span>
-and Haddam, Conn., Chester, Mass.,
-Unionville, Penn., Bakersville, N. C., etc.</p>
-<h3><a id="species_Labradorite">Labradorite</a>
-<br />(NaCa)AlSi&#8323;O&#8328;
-<br /><a href="#Plate_35">Pl. 35</a></h3>
-<p>Usually found in cleavable masses
-in granites and lavas; hardness, 6;
-specific gravity, 2.71; color gray or
-white, often with a play of colors;
-luster vitreous; translucent on thin edges.</p>
-<p>Labradorite is distinguished by having the two
-perfect cleavage planes meet at 86&deg; 14&prime;. The
-iridescent play of color is also very characteristic
-and is generally present. It is due to the
-inclusion of minute impurities. This feldspar
-is usually associated with granites or lavas in
-which the dark minerals predominate. It gets
-its name from being the feldspar of the granites
-of Labrador, and is also found in the granites of
-the central part of the Adirondack Mountains
-and the Wichita Mountains of Arkansas.</p>
-<h3 class="center"><span class="sc">The <a id="species_Pyroxene">Pyroxene</a> Group</span></h3>
-<p>The minerals of this group are generally associated
-with feldspars, and make the dark-colored
-component of granites, gneisses and
-lavas. This is especially true of those which
-have some iron in the crystal. Pyroxenes are
-salts of metasilicic acid (H&#8322;SiO&#8323;), in which the
-hydrogen (H) has been replaced by calcium,
-magnesium, iron, etc. The commoner minerals
-are orthorhombic or monoclinic, and all agree in
-their crystal habit, being short stout prisms, with
-the vertical edges so beveled that a cross section
-is eight-sided. The cleavage is good in two directions,
-<span class="pb" id="Page_117">117</span>
-parallel to the beveling faces (m in figure
-b, <a href="#Plate_36">Plate 36</a>), and they intersect at an angle of
-87&deg;. This is very characteristic, and if one has a
-crystal broken across, it is easy to see and measure
-this angle of intersection. These pyroxenes
-have the same chemical composition as the corresponding
-series of amphiboles, but the two are
-distinguished by several features. Pyroxenes
-are short and stout crystals, while amphiboles
-are long and either blade- or needle-like; pyroxenes
-are eight-sided in cross section, while
-amphiboles are six-sided; in pyroxenes the cleavage
-planes intersect at 87&deg;, while in amphiboles
-they intersect at 55&deg;. The minerals of this group
-are most frequently one of the components of a
-lava or granite, and are less frequently associated
-with metamorphic rocks. Three are common;
-enstatite, hypersthene, and augite.</p>
-<h3><a id="species_Enstatite">Enstatite</a>
-<br />MgSiO&#8323;</h3>
-<p>Usually occurs in lamellar or fibrous-lamellar
-masses in dark lavas;
-hardness, 5.5; specific gravity, 3.3;
-color gray, bronze or brown; luster vitreous,
-translucent on thin edges.</p>
-<p>Enstatite rarely occurs in crystals, but when it
-does they are orthorhombic. Usually it is in irregular
-masses with the cleavage angles, typical
-of pyroxene. The color is light, that is gray or
-brownish, and the streak white or nearly so. In
-most respects it is similar to hypersthene, which
-has the same composition, except that a large
-part of the magnesium is replaced by iron, and
-there are all sorts of gradations between the two
-minerals. When some iron takes the place of
-<span class="pb" id="Page_118">118</span>
-magnesium, the color darkens to, or towards
-bronze, until when about a third of the magnesium
-is so replaced, and the color is fully bronze,
-this variety is called <i>bronzite</i>. Bronzite is present
-in some of the dark lavas like gabbro and
-peridotite. Enstatite is found in the Adirondack
-Mountains, at Brewster and Edwards, N. Y., etc.</p>
-<h3><a id="species_Hypersthene">Hypersthene</a>
-<br />(MgFe)SiO&#8323;</h3>
-<p>Occurs in cleavable masses in
-dark lavas; hardness, 5.5; specific
-gravity, 3.4; color dark-brown or
-greenish-brown; luster vitreous; translucent on
-thin edges.</p>
-<p>Hypersthene is a pyroxene in which magnesium
-and iron are present in about equal quantities.
-It is similar to enstatite, except that the
-color is darker, and the streak gray or brownish-gray
-in color. These two minerals grade into
-each other, so that there are cases where it is
-simply a matter of preference as to which name
-should be given to the mineral. This form is
-associated with dark lavas, of the gabbro or
-peridotite type, in such places as the Adirondack
-Mountains, Mount Shasta in California, Buffalo
-Peaks, Colo., etc.</p>
-<h3><a id="species_Augite">Augite</a>
-<br />CaMg(SiO&#8323;)&#8322;, MgAlSiO&#8326; + Fe&#8322;O&#8323;
-<br /><a href="#Plate_36">Pl. 36</a></h3>
-<p>Usually occurs in short stout
-monoclinic crystals; hardness, 5.5;
-specific gravity, 3.3; color dark-green
-to black; luster vitreous;
-translucent on thin edges.</p>
-<p>Augite is a complex pyroxene having some iron
-and aluminum always present in it, but the
-amount not a fixed quantity. It is by far the
-<span class="pb" id="Page_119">119</span>
-commonest of the pyroxenes and has a wide distribution,
-both in the sorts of lavas in which it
-appears, and in the world. It is commonly
-the dark component of such lavas, as gabbros and
-peridotites, and also is common in metamorphic
-rocks, especially impure crystalline limestones.
-It is found at Raymond and Mumford, Me.,
-Thetford, Vt., Canaan, Conn., in Westchester,
-Orange, Lewis and St. Lawrence Counties of N.
-Y., in Chester Co., Penn., at Ducktown, Tenn.,
-Templeton, Canada, etc.</p>
-<h3 class="center"><span class="sc">The <a id="species_Amphibole">Amphibole</a> Group</span></h3>
-<p>The amphiboles are a group of minerals made
-up of the same chemical elements as the pyroxenes,
-but with the molecular arrangement different,
-which appears in the forms of the crystals.
-The commoner ones are all monoclinic but contrast
-with the pyroxenes as follows. Amphiboles
-are long and slender crystals, while pyroxenes
-are short and stout; amphiboles are six-sided,
-while pyroxenes are eight-sided; amphiboles
-have the two perfect cleavages intersecting at
-55&deg; and 125&deg;, while those of pyroxene intersect
-at 87&deg; and 93&deg;. With the above in mind it is
-easy to place the minerals in their proper group,
-but inside the group it is not always so easy to
-distinguish one from another. This group is
-associated rather with metamorphic rocks than
-with igneous rocks, with which the pyroxenes are
-mostly associated. The three commoner minerals
-of the group are tremolite, actinolite, and
-hornblende.</p>
-<div class="pb" id="Page_120">120</div>
-<h3><a id="species_Tremolite">Tremolite</a>
-<br />(CaMg)&#8323;(SiO&#8323;)&#8324;
-<br /><a href="#Plate_37">Pl. 37</a></h3>
-<p>Occurs in long prismatic crystals
-or in columnar or fibrous masses;
-hardness 5.5; specific gravity, 3;
-color white to gray; luster vitreous; transparent
-on thin edges.</p>
-<p>The long prismatic crystals of tremolite occur
-especially where dolomitic limestones have been
-altered by metamorphism. Sometimes these
-crystals grow side by side, making fibrous masses,
-where the long slender crystals can be picked
-apart with the fingers, and yet are flexible, and
-tough enough so that they can be felted together.
-This is termed asbestos, which, because it is
-infusible and a poor conductor of heat, is much
-used to make insulators, fire-proof shingles, and
-all sorts of fireproof materials. The varieties in
-which the crystals are finer and silky in appearance,
-like the one illustrated on <a href="#Plate_38">Plate 38</a> are
-termed <i>amianthus</i>. There are other minerals,
-such as actinolite and serpentine, which occur in
-the same manner, and are also called asbestos, the
-serpentine variety being just now the most important
-commercially.</p>
-<p>Tremolite is found at Lee, Mass., Canaan,
-Conn., Byram, N. J., in Georgia, etc.</p>
-<h3><a id="species_Actinolite">Actinolite</a>
-<br />(CaMgFe)&#8323;(SiO&#8323;)&#8324;</h3>
-<p>Occurs in radiating crystals, or
-in fibrous masses; hardness, 5.5;
-specific gravity 3; color pale- to dark-green;
-luster vitreous; translucent on thin edges.</p>
-<p>Except for its green color, this mineral is very
-like tremolite. The difference between the two is
-due to the small amount of iron in the actinolite.
-It is usually found in schists, and the radiating
-<span class="pb" id="Page_121">121</span>
-character of the crystal groups is enough to
-determine the mineral, if it is already clear that
-it is one of the amphiboles. Occasionally it occurs
-with the crystals parallel to each other, making
-one of the forms of asbestos.</p>
-<p>Actinolite is found at Warwick, Edenville, and
-Amity in Orange Co., N. Y., at Franklin and
-Newton, N. J., Mineral Hill and Unionville,
-Penn., Bare Hills, Md., Willis Mt., Va., etc.</p>
-<h3><a id="species_Hornblende">Hornblende</a>
-<br />(CaMgFe)&#8323;(SiO&#8323;)&#8324;CaMgAl&#8322;(SiO&#8324;)&#8323;
-<br /><a href="#Plate_37">Pl. 37</a></h3>
-<p>Occurs in well-defined crystals, in
-grains and in masses; hardness, 5.5;
-specific gravity 3.2; color black,
-dark-green, or dark-brown; luster
-vitreous; translucent on thin edges.</p>
-<p>In composition hornblende corresponds to
-augite, but occurs in long slender, six-sided
-crystals with cleavage planes intersecting at 55&deg;,
-so that it is a typical amphibole. It occurs in a
-very wide range of rocks, such as granite, syenite,
-diabase, and gabbro; and in such metamorphic
-rocks as schists and gneisses; and sometimes
-igneous rocks are made up almost entirely of
-hornblende, when they are known as amphibolites
-or hornblendite. It is found all through the
-New England States, down along the Piedmont
-Plateau, through the Blue Ridge Mountains,
-and in many of the western mountainous areas.</p>
-<h3 class="center"><span class="sc">The <a id="species_Garnet">Garnet</a> Group</span></h3>
-<p>The garnets are a series of double silicates,
-which occur with surprisingly uniform characters.
-They are all isometric, and occur either
-<span class="pb" id="Page_122">122</span>
-as dodecahedrons, or as the 24-sided figure (the
-trapezohedron), which is formed by the beveling
-of the edges of the dodecahedron, and developing
-these new faces to the exclusion of the dodecahedron
-faces. Combinations of the dodecahedron
-and trapezohedron (36 faces) may occur. All
-the garnets have a hardness of 7 to 7.5, and the
-specific gravity runs from 3.2 to 4.3, according to
-the composition. In size they run from as small
-as a grain of sand up to as large as a boy&rsquo;s marble,
-and occasionally even to four inches in diameter.
-The color varies with the composition, from colorless
-to yellow, red, violet, or green. There is no
-cleavage, and the luster is always vitreous.</p>
-<p>Garnets are usually accessory minerals, found
-in metamorphic rocks, though they are sometimes
-also present in granites and lavas. They are
-always segregations which have taken place in
-the presence of high temperatures. When clear
-and perfect several of the garnets are used as
-gems. On the other hand some of the common
-garnets occur in such quantities that they are
-crushed and used as abrasives, for such work
-as dental polishes, or for leather and wood
-polishing.</p>
-<p>The following is the composition of some of the
-commoner garnets.</p>
-<table class="center" summary="">
-<tr><td class="l">Ca&#8323;Al&#8322;(SiO&#8324;)&#8323; </td><td class="l">= grossularite</td></tr>
-<tr><td class="l">Mg&#8323;Al&#8322;(SiO&#8324;)&#8323; </td><td class="l">= pyrope</td></tr>
-<tr><td class="l">Fe&#8323;Al&#8322;(SiO&#8324;)&#8323; </td><td class="l">= almandite</td></tr>
-<tr><td class="l">Mn&#8323;Al&#8322;(SiO&#8324;)&#8323; </td><td class="l">= spessartite</td></tr>
-<tr><td class="l">Ca&#8323;Fe&#8322;(SiO&#8324;)&#8323; </td><td class="l">= andradite</td></tr>
-<tr><td class="l">Ca&#8323;Cr&#8322;(SiO&#8324;)&#8323; </td><td class="l">= uvarovite</td></tr>
-</table>
-<div class="pb" id="Page_123">123</div>
-<p><b>Grossularite</b> is chiefly found in crystalline
-limestones, which have resulted either from
-contact with lavas, or from general metamorphism
-of impure limestones. These garnets are
-colorless to white, or more often shades of yellow,
-orange, pink, green or brown, according to traces
-of impurity which they may contain. The
-cinnamon-colored variety from Ceylon is termed
-<i>cinnamon stone</i>, and is a fairly popular gem.</p>
-<p><b>Pyrope</b> is a deep-red color and when perfect
-is highly prized as a gem. It is found in dark-colored
-igneous rocks, like lavas, or serpentines.
-Some of the finest come from South Africa, where
-they are found in company with the diamond.</p>
-<p><b>Almandite</b> is dark-red to brown in color, the
-brownish-cast distinguishing it from pyrope.
-It is one of the garnets known as &ldquo;common garnet.&rdquo;
-In some cases it is clear and deep colored
-enough to be used as a gem, but mostly it is
-muddy in appearance. The name almandite
-comes from Alabanda, a city of the ancient district
-of Caria, Asia Minor, whence garnets were
-traded to ancient Rome. The finest garnets
-&ldquo;Sirian garnets&rdquo; came from the city of &ldquo;Sirian&rdquo;
-in Lower Burma, and were supposed to have been
-found near there, but careful investigation shows
-that no garnets occurred near there, and this
-town was therefore, even at that early time, a
-distributing point for garnets, found probably
-further to the east. The &ldquo;Sirian&rdquo; garnet had a
-violet cast and now the term is used to indicate a
-type of garnet, rather than a locality.</p>
-<p><b>Spessartite</b> is dark-hyacinth-red, or red with a
-violet-tinge, and is one of the less-common garnets.
-<span class="pb" id="Page_124">124</span>
-It is usually found in granites. The finest
-garnets of the type come from Amelia Court
-House, Va., which has yielded some ranging
-from one up to a hundred carats.</p>
-<p><b>Andradite</b> is another garnet which is termed
-&ldquo;common garnet.&rdquo; It is red in color, but with a
-yellowish-cast which distinguishes it from almandite,
-but these two are not easy to separate.
-It is found mostly in metamorphosed limestones.
-One variety is black in color and called <i>malanite</i>.
-It is found in lavas. The common yellowish-red
-garnets are found through New England and the
-Piedmont Plateau.</p>
-<p><b>Uvarovite</b> is a rare garnet of emerald-green
-color, found in association with chromium ores.</p>
-<p>The number of localities for garnets is so great
-that a list would suggest most of the regions
-where metamorphic rocks occur, as all over New
-England, throughout the Piedmont Plateau, the
-Rocky Mountains, etc. Certain fine clear garnets,
-found in Montana, northeastern Arizona, and
-northwestern New Mexico are sold under the
-trade name of &ldquo;Montana, Arizona or New
-Mexico rubies.&rdquo; These are of fine quality and
-are mostly collected by the Indians from the ant
-hills and scorpion&rsquo;s nests of those regions.</p>
-<p>Garnets are among the earliest stones mentioned
-in ancient languages, as would be expected
-from the way these hard and beautiful
-crystals weather out of the much softer metamorphic
-rocks, like schists. In the past they,
-with most any other translucent red stone, were
-included under the name <i>carbuncle</i>. This, however,
-is not the name of any mineral, but refers
-<span class="pb" id="Page_125">125</span>
-rather to a mode of cutting, <i>en cabochon</i> or with
-a convex surface.</p>
-<h3 class="center"><span class="sc">Glucinum</span></h3>
-<p>Glucinum is a rare metal, silvery-white in
-color, malleable, and melting at a fairly low
-temperature. It is found in the mineral beryl,
-from which has come the alternative name <i>beryllium</i>.
-The name comes from the sweet taste of
-its salts. Except for beryl its minerals are rare,
-and the metal has found but few uses for man.</p>
-<h3><a id="species_Beryl">Beryl</a>
-<br />Gl&#8323;Al&#8322;(SiO&#8323;)&#8326;
-<br /><a href="#Plate_39">Pl. 39</a></h3>
-<p>Occurs in hexagonal crystals in
-granites, gneisses and mica schists;
-hardness, 7.5; specific gravity, 2.7;
-color usually some tint of green; luster vitreous;
-transparent on thin edges.</p>
-<p>When this mineral occurs in coarse hexagonal
-prisms, with or without faces on the ends, it is
-known as beryl; when the crystals are clear and
-perfect and of a dark-green color, they are of gem
-value and are termed <i>emerald</i>; when of a light-green
-color, they are <i>aquamarine</i>; and when
-bright-yellow in color, they are the <i>golden beryl</i>.
-There is little difficulty in determining beryl, for
-only apatite occurs in such crystals, and is green,
-and this latter mineral has a hardness of only 5.
-There is an imperfect basal cleavage.</p>
-<p>Ordinary beryl is fairly common in granites of
-the pegmatite sort, and less common in gneisses
-and mica-schists. This type often furnishes
-crystals of large size, up to two and three feet in
-diameter.</p>
-<div class="pb" id="Page_126">126</div>
-<p>Beryl which is free from cracks and inclosures,
-so it can be used as a gem, is so rare, that the
-emerald has a value above that of the diamond,
-and second only to the ruby. It is one of the
-gems with a long history, having been quarried
-on the west coast of the Red Sea at least 1650
-<span class="small">B.C.</span> by the Egyptians. To early people it had a
-power to quicken the prophet instinct and made
-the wearer see more clearly. The Spanish conquistadores
-found fine emeralds among the treasures
-of both Mexico and Peru. In the United
-States, Stony Point, N. C., was a notable locality
-for these gems, but now seems to have been exhausted.
-The name emerald has been applied to
-many other green stones, usually with some geographical
-modification, as &ldquo;Oriental emerald&rdquo;
-which is green corundum, &ldquo;Brazilian emerald&rdquo;
-which is tourmaline, etc.</p>
-<p>Giant beryls have been found at Acworth and
-Grafton, N. H., and at Royalston, Mass. Localities
-for ordinary beryl are Albany, Norway,
-Bethel, Hebron, Paris, and Topsham, Me., Barre,
-Goshen and Chesterfield, Mass., New Milford
-and Branchville, Conn., Chester and Mineral
-Hill, Penn., Stony Point, N. C., and many other
-localities in the Appalachians; also Mount
-Antero, Colo., and in the Black Hills of South
-Dakota.</p>
-<h3><a id="species_Sodalite">Sodalite</a>
-<br />Na&#8324;Al&#8323;Cl(SiO&#8324;)&#8323;</h3>
-<p>Occurs in irregular masses, sometimes
-in dodecahedrons; hardness,
-5.5-6; specific gravity, 2.3; color
-deep-blue to colorless; streak white; luster vitreous;
-translucent on thin edges.</p>
-<div class="pb" id="Page_127">127</div>
-<p>This striking mineral, with its deep-blue to
-azure color, is not easily confused with any other.
-It is characteristic of soda-rich igneous rocks
-such as syenite and some lavas. In this country
-it is found at Litchfield, Me., and Salem, Mass.</p>
-<h3><a id="species_Zircon">Zircon</a>
-<br />ZrSiO&#8324;
-<br /><a href="#Plate_39">Pl. 39</a></h3>
-<p>Usually occurs in tetrahedral crystals
-in igneous rocks; hardness, 7.5;
-specific gravity, 4.7; color brown;
-luster vitreous; translucent on thin edges.</p>
-<p>Zircon, the mineral of the rare earth element
-zirconium, nearly always occurs in light-colored
-igneous rocks, like syenite. It may occur in
-schists or gneisses, but in these rocks the crystals
-are of microscopic size. Because of their great
-hardness and insolubility, zircon crystals resist
-weathering and are often found, along with gold,
-cassiterite, or magnetite, in sands which have
-resulted from the disintegration of syenite rocks.</p>
-<p>Zircon refracts and disperses light to a degree
-second only to the diamond, so that clear crystals
-are sought as gems. They are often called &ldquo;Matura
-diamonds&rdquo; because of their abundance
-at Matura, Ceylon. When the crystals are
-colorless or smoky they are termed <i>jargons</i> or
-<i>jargoons</i>; when of a red-orange hue, they are
-<i>hyacinth</i> or <i>jacinth</i>. Most of the zircon of gem-quality
-comes from Ceylon, where it is picked up
-as rolled-pebbles from the beds of brooks.</p>
-<p>The most remarkable American locality for
-zircon is near Green River, in Henderson Co.,
-N. C., where it is found abundantly in a decomposed
-pegmatite dike, from which many tons
-have been obtained. It is also found at Moriah,
-<span class="pb" id="Page_128">128</span>
-Warwick, Amity and Diana, N. Y., at Franklin
-Furnace, and Trenton, N. J., in the gold-bearing
-sands of California, etc.</p>
-<h3><a id="species_Cyanite">Cyanite</a>
-<br />Al&#8322;SiO&#8325;
-<br /><a href="#Plate_40">Pl. 40</a></h3>
-<p>Occurs in long blade-like crystals
-in gneisses and schists; hardness, 7
-at right angles to the length, and
-4.5 parallel to the length; specific gravity, 3.6;
-color blue; luster vitreous; translucent on thin
-edges.</p>
-<p>There are only a few blue minerals, and the
-way in which cyanite occurs in long thin blade-like
-crystals is entirely characteristic. If more
-is still wanted to determine this mineral, its
-unique character in having the great hardness 7
-when scratched parallel to the length, and only
-4.5 when scratched crossways, will settle any
-doubts.</p>
-<p>The mineral <i>sillimanite</i> has the same composition
-as cyanite, but is fibrous in habit and has the
-hardness 6.5. If cyanite is heated to 1350&deg; C.
-it changes its character and becomes sillimanite.</p>
-<p>Cyanite is found as an accessory mineral in
-metamorphic rocks, such as gneiss and schist, at
-Chesterfield, Mass., Litchfield and Oxford, Conn.,
-in Chester Co., Penn., in North Carolina, etc.</p>
-<h3 class="center"><span class="sc">The <a id="species_Mica">Mica</a> Group</span></h3>
-<p>The micas are very common minerals, easily
-recognized by their very perfect basal cleavage,
-as a result of which thin sheets, often less than a
-thousandth of an inch in thickness, readily split
-off. These are tough and elastic, which distinguishes
-<span class="pb" id="Page_129">129</span>
-mica from the chlorite group in which
-there is similar basal cleavage, but the sheets are
-not elastic.</p>
-<p>Micas are complex silicates of aluminum, with
-potassium, iron, lithium, magnesium and hydrogen.
-They are one of the principle components
-of many granites, gneisses, and schists. This
-mineral is always crystalline, being in the monoclinic
-system, but occurring in six-sided prisms.
-The cleavage is so dominant a character that the
-crystal form is usually overlooked, as it is seldom
-requisite in determining this mineral. The size
-of the sheets of mica depend on the size of the
-crystals, the larger sheets expressing great slowness
-in cooling from the original magmas. Sometimes
-the crystals may be two or even three feet
-in diameter. The hardness is not great, ranging
-between 2 and 3. The specific gravity lies between
-2.7 and 3.2. The color varies according to
-the composition, from silvery-white, through
-gray, pink, and green to black. The luster is
-vitreous to pearly, sometimes gleaming in the
-darker-colored varieties. The commoner types
-of mica are as follows:</p>
-<dl class="undent"><dt>Muscovite, H&#8322;KAl&#8323;(SiO&#8324;)&#8323; or potash mica.</dt>
-<dt>Lepidolite, LiK(Al&#8322;OH&middot;F)Al(SiO&#8323;)&#8323; or lithia mica.</dt>
-<dt>Biotite, (HK)&#8322;(MgFe)&#8322;Al&#8322;(SiO&#8324;)&#8323; or iron mica.</dt>
-<dt>Phlogopite, H&#8322;KMg&#8323;Al(SiO&#8328;)&#8323; or magnesia mica.</dt></dl>
-<p><b>Muscovite</b> is colorless, silvery-white, gray or
-sometimes pale-green or brown. It gets its name
-from Moscow where it was early used for window
-<span class="pb" id="Page_130">130</span>
-panes, and it is still used for stove and furnace
-doors, as well as in electric work, for a lubricant,
-etc.</p>
-<p>The best crystals occur in granites, in the
-coarse varieties of which large crystals may be
-obtained. It is found also as small scales in
-gneisses and schists, and when weathered from
-its original rocks it may be present in sandstones
-and shales. Muscovite is always in its origin an
-elementary component of deep-seated igneous
-rocks, like granite; but is never a component of
-extruded lavas. <i>Sericite</i> is muscovite which has
-been secondarily produced by the alteration of
-other minerals into muscovite, as when feldspar,
-cyanite, topaz, etc., have been modified by the
-presence of heat and hot vapors, when near lavas
-that have come in contact with other rocks.
-Muscovite is very resistant to alteration by
-weathering, but when it does change, the greater
-part of it becomes kaolin. It is found at Acworth
-and Grafton, N. H., in plates, sometimes a yard
-across at Paris, Me., Chesterfield and Goshen,
-Mass., Portland and Middletown, Conn., at
-Warwick, Edenville, etc., N. Y., and all down the
-Appalachian Mts., also in the Rocky Mts., the
-Cascade Range, etc.</p>
-<p><b>Lepidolite</b> is pink or lilac in color and occurs in
-scaly masses, mostly in granites. It does not
-come in large crystals. Lepidolite is found
-at Paris and Hebron, Me., Middletown, Conn.,
-Pala, Calif., etc.</p>
-<p><b>Biotite</b> is dark-brown or black mica. Like
-muscovite it is very common, making one of the
-chief components of granites, gneisses and schists;
-<span class="pb" id="Page_131">131</span>
-and, unlike muscovite, it may occur in extrusive
-lavas, like trachyte, andesite, and basalt. It
-resists weathering much less than muscovite, so
-that, when the rocks of which it is a component
-disintegrate, biotite is usually altered to kaolin
-and other compounds. It is likely to occur in
-good-sized crystals, especially at Topsam, Me.,
-Moriah, N. Y., Easton, Penn., etc.</p>
-<p><b>Phlogopite</b> is pale-brown, often coppery in
-color, and is most likely to occur in serpentines,
-or crystalline limestones or dolomites, often in
-fine crystals, of good size. While one of the less
-abundant micas, this is found at Gouverneur,
-Edwards, and Warwick, N. Y., Newton, N. J.,
-and Burgess, Canada.</p>
-<h3><a id="species_Topaz">Topaz</a>
-<br />Al&#8322;F&#8322;SiO&#8324;
-<br /><a href="#Plate_41">Pl. 41</a></h3>
-<p>Occurs in crystals mostly; hardness,
-8; specific gravity, 3.5; colorless
-to pale-yellow; luster vitreous;
-transparent on thin edges.</p>
-<p>Topaz may be colorless, but is more often some
-shade of yellow, and at times brown or even blue.
-Its hardness is characteristic, there being but few
-minerals as hard, and it is used to represent the
-hardness 8 in the Moh&rsquo;s scale. The crystals are
-orthorhombic prisms, with the edges of the
-prism beveled and often striated. The ends of
-crystals usually terminate with a basal plane,
-parallel to which there is good cleavage. Between
-this basal plane and the prism faces there
-are usually several sets of small faces as indicated
-on <a href="#Plate_41">Plate 41</a>.</p>
-<p>This mineral, as is also true of most minerals
-containing fluorine, is one of those which have
-<span class="pb" id="Page_132">132</span>
-crystallized out from hot vapors, escaping from
-igneous magmas. It is associated with such
-minerals, as tourmaline, beryl, fluorite, and cassiterite,
-and occurs mostly in cavities or seams,
-in or near granites.</p>
-<p>Ordinary topaz, which means crystals that are
-imperfect by reason of tiny cracks and impurities
-is not very rare, but crystals which are perfect
-and clear in color are considered gems. Most of
-the gem-topaz is some shade of yellow, but may
-be brown or blue, never, however, pink, as is often
-seen in jewelry. The &ldquo;pinking&rdquo; is artificial, and
-done by packing yellow or brown topaz in magnesia,
-asbestos, or lime, and then heating it
-slowly to red heat, after which it is cooled slowly.
-If underheated the color is salmon, if overheated
-all color disappears. Topaz has been a gem for
-centuries, the earliest records coming from Egypt.
-The name comes from <i>topazios</i>, meaning to seek,
-because the earliest known locality, from which
-it was gathered, was a little island of that name
-in the Red Sea, and this island was often surrounded
-by fog and hard for those early mariners
-to find. Here by mandate of the Egyptian kings
-the inhabitants had to collect topazes, and deliver
-them to the gem-cutters of Egypt for polishing.</p>
-<p>Several yellow stones are called topaz, as the
-&ldquo;Oriental topaz&rdquo; which is corundum and more
-valuable than topaz itself; and several varieties of
-yellow quartz, which go under such names as
-&ldquo;Saxon,&rdquo; &ldquo;Scotch,&rdquo; &ldquo;Spanish,&rdquo; and &ldquo;smoky&rdquo;
-topaz. When topaz occurs colorless as in Siberia,
-the Ural Mountains, and in the state of Minas
-<span class="pb" id="Page_133">133</span>
-Geraes, Brazil, in all of which places it is found
-as pebbles in brooks, it goes under the name of
-&ldquo;slave&rsquo;s diamonds.&rdquo; Brazil is today the chief
-source of gem-quality topaz.</p>
-<p>Ordinary topaz is found in this country at
-Trumbull, Conn., Crowder&rsquo;s Mt., N. C., Thomas
-Mts., Utah, in Colorado, Missouri, and California,
-etc.</p>
-<h3><a id="species_Staurolite">Staurolite</a>
-<br />FeAl&#8325;OH(SiO&#8326;)&#8322;
-<br /><a href="#Plate_41">Pl. 41</a></h3>
-<p>Occurs in orthorhombic crystals;
-hardness, 7.5; specific gravity, 3.7;
-color brown; luster resinous; translucent
-on thin edges.</p>
-<p>This mineral occurs about equally abundantly
-in simple crystals similar to the outline on <a href="#Plate_41">Plate 41</a>,
-and in twins which have grown through each
-other either at 90&deg; or at 60&deg;. The color is either
-brown or reddish-brown. In all cases it is an
-accessory mineral, occurring in metamorphic
-rocks, usually schists, though less frequently
-in slates and gneisses.</p>
-<p>From the seventeenth century on, it has been
-used as a baptismal stone, and worn as a charm,
-legends stating that it fell from the heavens.
-Fine crystals have been found in Patrick County,
-Va., and there is in this region the legend, that
-when the fairies heard of the crucifixion of Christ,
-they wept and their tears falling crystallized in
-the form of crosses, such as the one shown on
-<a href="#Plate_41">Plate 41</a>.</p>
-<p>Staurolite is found in the schists of New England
-as at Windham, Me., or Chesterfield, Mass.,
-and all down the east side of the Appalachian
-Mountains to Georgia.</p>
-<div class="pb" id="Page_134">134</div>
-<h3><a id="species_Olivine">Olivine</a>
-<br />(MgFe)&#8322;SiO&#8324;
-<br /><i>Peridot</i> or <i>Chrysolite</i></h3>
-<p>Occurs in grains and irregular
-masses in dark lavas; hardness 6.5
-to 7; specific gravity 3.3; color
-bottle- to olive-green; luster vitreous;
-translucent on thin edges.</p>
-<p>Olivine rarely occurs in crystals, but when it
-does they belong to the orthorhombic system.
-The dark-green grains or masses are recognized
-by the color, considerable hardness and indistinct
-cleavage. Serpentine may have a similar
-color, but its hardness is only 4. In hydrochloric
-acid olivine decomposes to a gelatinous mass.</p>
-<p>Olivine is typically one of the constituents of
-the dark lavas, like basalt, gabbro, or peridotite.
-It is also a common mineral in meteorites.
-Olivine, in the presence of water, alters to
-other minerals, especially serpentine, with great
-facility.</p>
-<p>It occurs fairly widely wherever the dark lavas
-are present, as in the White Mountains of N. H.,
-in Loudoun Co., Va., in Lancaster Co., Penn.,
-and in many localities in the Rocky Mountains
-and Cascade Range.</p>
-<h3><a id="species_Epidote">Epidote</a>
-<br />Ca&#8322;(AlOH)(AlFe&#8322;)(SiO&#8324;)&#8323;
-<br /><a href="#Plate_42">Pl. 42</a></h3>
-<p>Occurs in grains or columnar
-masses; hardness, 6.5; specific gravity
-3.4; color green, usually a
-pistachio or yellow-green; luster
-vitreous; translucent on thin edges.</p>
-<p>Rarely epidote occurs in crystals, which belong
-to the monoclinic system, and may be either
-short like the diagrams on <a href="#Plate_42">plate 42</a> or long and
-needle-like. The color and hardness will suffice
-to determine this mineral, as almost no other has
-<span class="pb" id="Page_135">135</span>
-the peculiar yellowish-green color which is
-characteristic of this form.</p>
-<p>Epidote occurs primarily in metamorphic
-rocks at or near the contact with igneous rocks;
-or it may be a secondary mineral resulting from
-the weathering of granites, especially along seams.
-It sometimes occurs with hornblende in highly
-folded schists, as in New York City. It is often
-a mineral which has resulted from the alteration
-of other minerals, as pyroxene, amphibole,
-biotite, or even feldspars.</p>
-<p>It is found at Chester and Athol, Mass.,
-Haddam, Conn., Amity, Munroe and Warwick,
-N.Y., East Branch, Penn., in the Lake Superior
-region, in the Rocky Mountains, etc.</p>
-<h3><a id="species_Tourmaline">Tourmaline</a>
-<br />(FeCrNaKLi)&#8324;Mg&#8321;&#8322;B&#8326;Al&#8321;&#8326;H&#8328;Si&#8321;&#8322;O&#8326;&#8323;
-<br /><a href="#Plate_42">Pl. 42</a> &amp; <a href="#Plate_Frontispiece">frontispiece</a></h3>
-<p>Occurs in three-sided prismatic
-crystals; hardness, 7; specific gravity,
-3.1; colorless, red, green, brown,
-or black; luster vitreous; transparent
-on thin edges.</p>
-<p>Tourmaline is readily distinguished
-from other minerals, as it
-always occurs in long to short prisms, which are
-three-sided in cross section. There is also a
-tendency for the sides to be curved as seen on
-the end view of D, <a href="#Plate_42">Pl. 42</a>. Frequently the vertical
-edges of the prism are beveled with one, two
-or three faces, grouped about each of the three
-original edges, and there are often striations on
-the prism faces. The ends are terminated by a
-low rhombohedron and again there may be a
-host of modifying faces on the edges and corners
-of the end. The common varieties are brown or
-<span class="pb" id="Page_136">136</span>
-black in color, but occasionally there may occur
-green, red, yellow or almost any color. When
-the crystals are perfect, that is free from impurities
-and without tiny cracks, tourmaline becomes
-a gem of popularity and value.</p>
-<p>Tourmaline is very complex in composition
-and may vary considerably, the sodium, potassium,
-lithium, magnesium, and iron being either
-more or less abundant or even lacking. The color
-is to some extent dependent on the proportions
-of these elements present, the dark varieties
-having more iron, and the light colored tourmalines
-lacking it. This mineral is one of those
-which form from superheated vapors, escaping
-from molten magmas. It will therefore occur in
-veins, often associated with copper minerals, in
-crystalline limestones, or in cavities in granites,
-where it is associated with such minerals, as
-beryl, apatite, fluorite, topaz, etc.</p>
-<p>If heated tourmaline crystals develop electricity,
-with the effect of making one end a positive
-and the other a negative pole, and then will attract
-bits of straw, ashes, etc. It was first introduced
-into Europe about 1703 from India, and
-its vogue as a gem has greatly increased since it
-was found on Mount Mica near Paris, Me. This
-Paris, Me., locality was discovered by two boys,
-amateur mineralogists, Elijah L. Hamlin and
-Ezekiel Holmes, who in 1820 were returning
-home from a trip hunting for minerals, when, at
-the root of a tree, they discovered some gleaming
-green substance. It proved to be gem-quality
-tourmaline. A snow storm that night buried
-their &ldquo;claim,&rdquo; but next spring it was visited and
-<span class="pb" id="Page_137">137</span>
-several fine crystals found. Later this locality
-was systematically worked, and over $50,000
-worth of tourmaline taken from the pegmatite
-seam in the granite, which lay under the crystals
-found on the surface. The figure in the <a href="#Plate_Frontispiece">frontispiece</a>
-is one of the crystals from there.</p>
-<p>Well known localities are Paris and Hebron,
-Me., Goshen and Chesterfield, Mass., Acworth
-and Grafton, N. H., Haddam and Munroe,
-Conn., Edenville and Port Henry, N. Y., Jefferson
-Co., Colo., San Diego Co., Calif., etc.</p>
-<h3><a id="species_Kaolinite">Kaolinite</a>
-<br />H&#8324;Al&#8322;Si&#8322;O&#8329;
-<br /><i>Kaolin</i></h3>
-<p>Usually found in whitish clay-like
-masses; hardness, 2; specific
-gravity, 2.6; color white to grayish
-or yellowish; luster dull.</p>
-<p>Kaolinite does not generally occur in crystals,
-though crystals of microscopic size and monoclinic
-forms have been found. It is a secondary
-mineral resulting from the decomposition by
-weathering of feldspars, the calcium, potassium
-or sodium having been replaced by water. When
-found in place it is generally white or nearly
-white, and is characterized by its greasy feel.</p>
-<p>As granites or other feldspar-bearing rocks are
-weathered away, the kaolin is washed out by
-water, and with other fine material is carried
-down into lakes or the sea, where it settles to the
-bottom and is known as clay. Clay is kaolin
-with more or less impurities.</p>
-<p>Pure kaolin is used for the manufacture of
-china and white porcelain ware; but when it is
-impure, especially when it has iron in it, baking
-causes the product to turn red or brown, so
-<span class="pb" id="Page_138">138</span>
-that it is only suitable for making tile, bricks,
-etc.</p>
-<p>It is found almost anywhere that feldspar
-rocks are, or have been, exposed to weathering.</p>
-<h3><a id="species_Talc">Talc</a>
-<br />H&#8322;Mg&#8323;(SiO&#8323;)&#8324;</h3>
-<p>Occurs in scales, or in fibrous,
-scaly or compact masses; hardness,
-1; specific gravity, 2.7; color white,
-gray or pale-green; luster pearly; translucent on
-thin edges.</p>
-<p>This mineral is as soft as any, only graphite
-and molybdenite being of the same hardness, but
-both these latter two have a black streak, while
-the streak of talc is white. The greasy feel is
-also characteristic. Talc is very seldom found in
-crystals, but if they are found, they will appear like
-flakes and have a hexagonal cross section, though
-in reality they belong to the monoclinic system.</p>
-<p>Talc is a secondary mineral which usually
-results from the exposure of magnesium silicates,
-such as pyroxenes or amphiboles, to moisture.
-In this case, in-as-much as the original rocks were
-metamorphic in origin, the talc therefrom will
-occur in old metamorphic regions. Some talc is
-also formed by the action of silica-bearing waters
-on dolomite. This is likely to be the case near
-the contact between dolomite and igneous rocks.
-Talc is closely related to serpentine and likely
-to be found in the same regions.</p>
-<p>Talc has come to have a considerable use.
-Some of it is compact and then called soapstone,
-and this was used by the ancient Chinese to make
-images and ornaments; and our North American
-Indians used it to make large pots, to serve as
-<span class="pb" id="Page_139">139</span>
-containers for liquids. Some of these pots have
-been carved out with great skill, so as to be fairly
-light in proportion to what they would hold.
-Pipes and images were also carved from soapstone.
-Today we still cut soapstone into slabs
-to make mantels, laundry tubs and sinks. The
-scaly and fibrous varieties are ground, and used
-in making paper, paint, roofing, rubber, soap,
-crayons, toilet powders, etc. The United States
-produce and use over half the world&rsquo;s production,
-our industries requiring over 100,000 tons of talc
-a year. Of this 38% goes into paper, 23% into
-paint, 18% into roofing, and so on down to toilet
-powder which uses 2&frac12;%, or 2,500 tons a year.</p>
-<p>Talc is found in metamorphosed regions, that
-is in New England, all down the east side of the
-Appalachian Mts., in the Rocky Mts., and the
-Cascade Ranges, with a large number of local
-occurrences. New York State is the leading producer.</p>
-<h3><a id="species_Serpentine">Serpentine</a>
-<br />H&#8324;Mg&#8323;Si&#8322;O&#8329;
-<br /><a href="#Plate_43">Pl. 43</a></h3>
-<p>Occurs in compact, granular or
-fibrous masses; hardness, 3; specific
-gravity, 2.6; color green; luster
-greasy; translucent on thin edges. Serpentine
-is never in crystals. Its color and hardness
-serve to distinguish it. Like talc it is a secondary
-mineral resulting from the alteration, in
-the presence of moisture, of pyroxenes, amphiboles,
-and especially, olivine. As these are often
-in metamorphic rocks, the serpentine is likely to
-be associated with metamorphic rocks. Some
-serpentine is also the result of the action of silica-bearing
-water on dolomite, and this is likely to
-<span class="pb" id="Page_140">140</span>
-occur in areas of sedimentary rocks. The fibrous
-variety of serpentine, <i>chrysolite</i>, usually occurs in
-seams or veins, and when the fibers are long, it is
-used as asbestos. This form of asbestos is the
-one most used commercially today, as there are
-remarkably large deposits of it in the Province of
-Quebec, which provide the major part of the
-world supply. In the United States it is also
-found in California and Arizona but only in
-moderate quantities.</p>
-<p>Massive serpentine is used in considerable
-quantities as an ornamental stone, the green
-color varied with streaks and blotches of white,
-yellow and red, due to various impurities, making
-it very effective. It is, however, only suitable
-for interior work as the weather quickly spoils
-the polished surface. This is further discussed
-under serpentine rock, <a href="#Page_245">page 245</a>.</p>
-<p>Serpentine is found at Newfane, Vt., Newburyport,
-Mass., Brewster, Antwerp, etc., N. Y.,
-Hoboken, N. J., in Pennsylvania, Maryland, etc.</p>
-<h3><a id="species_Chlorite">Chlorite</a>
-<br />H&#8328;(MgFe)&#8325;Al&#8322;(SiO&#8326;)&#8323;
-<br /><a href="#Plate_43">Pl. 43</a></h3>
-<p>Occurs in monoclinic crystals of
-six-sided outline, or in scaly flakes
-or masses; hardness, 2; specific
-gravity 2.8; color green; luster pearly
-on cleavage faces; translucent on thin edges.</p>
-<p>Chlorite is a family name, covering a series of
-closely related minerals, so similar in appearance
-that they are best considered under this common
-name. In many respects they resemble mica, in
-the shape of the crystals and the remarkable
-basal cleavage. At first glance it is easy to confuse
-the two, but chlorite scales are not elastic,
-<span class="pb" id="Page_141">141</span>
-and when bent, stay bent, instead of snapping
-back like mica. In fact they look like more or
-less rotted micas. This is more than appearance,
-for chlorites form as a result of the alteration of
-micas in the presence of moisture. They are
-then secondary, and will be found where mica-rocks
-have been weathered, as in granites and
-schists.</p>
-<p>They may be expected anywhere that micas
-have been long exposed, as in New England, the
-Rocky Mountains, or the Sierra Nevada or Cascade
-Ranges. Special localities are Brewster,
-N. Y., Unionville and Texas, Penn., etc.</p>
-<h3 class="center"><span class="sc">The Zeolites</span></h3>
-<p>The zeolites are a group of white minerals,
-with a pearly luster, light weight, and easy solubility
-in acids; which, because their contained
-water is lightly held, readily boil before the blowpipe.
-They are all secondary minerals, which
-result from the decomposition of feldspars, when
-exposed to weathering. They are almost universally
-found in seams and cavities of disintegrating
-lavas. From a group of a dozen or so,
-three are common enough to be considered here.
-They may be found by watching such places, as
-where trap rock is being quarried for road material,
-or being blasted for any reason.</p>
-<h3><a id="species_Analcite">Analcite</a>
-<br />Na&#8323;Al&#8322;Si&#8324;O&#8321;&#8323; + 2H&#8322;O
-<br /><a href="#Plate_44">Pl. 44</a></h3>
-<p>Occurs as trapezohedrons in seams
-and cavities in lavas; hardness, 5.5;
-specific gravity, 2.2; colorless, white
-or pink; luster vitreous; transparent
-on thin edges.</p>
-<div class="pb" id="Page_142">142</div>
-<p>Analcite usually occurs in the 24-sided form,
-known as a trapezohedron, as illustrated in figure
-A, <a href="#Plate_44">Pl. 44</a>; but it may also occur in cubes with the
-three faces of the trapezohedron on each corner.
-Small crystals are often colorless, but the larger
-ones are either white or pink, and are opaque.
-While the form is the same as that of garnets, the
-color, lesser hardness, and the occurrence in
-lavas will serve to distinguish this mineral. If
-placed in hydrochloric acid analcite dissolves
-to a gelatinous mass.</p>
-<p>It is always found in seams and cavities in
-lavas, as at Bergen Hill and Weehawken, N. J.,
-Westfield, Mass., in the Lake Superior region, etc.</p>
-<h3><a id="species_Natrolite">Natrolite</a>
-<br />Na&#8322;Al&#8322;Si&#8323;O&#8321;&#8320; + 2H&#8322;O
-<br /><a href="#Plate_44">Plate 44</a></h3>
-<p>Occurs as bristling crystals in
-seams and cavities in lavas; hardness,
-5.5; specific gravity, 2.2; colorless;
-luster vitreous; transparent on
-thin edges.</p>
-<p>Natrolite occurs as beautiful bristling tufts of
-needle-like crystals, each crystal an orthorhombic
-prism with a very low pyramid on the end.
-This mineral is so easily fusible that it can be
-melted in a candle flame, giving to the flame the
-characteristic yellow color due to sodium. In
-hydrochloric acid it dissolves to a gelatinous
-mass. It is always a secondary mineral in cavities
-and seams in disintegrating lavas, and the
-tuft-like manner of growth is so characteristic,
-that once seen, it will always be recognized.</p>
-<p>Natrolite is found at Weehawken and Bergen
-Hill, N. J., at Westfield, Mass., in the Lake
-Superior region, etc.</p>
-<div class="pb" id="Page_143">143</div>
-<h3><a id="species_Stilbite">Stilbite</a>
-<br />H&#8324;(CaNa&#8322;)Al&#8322;(SiO&#8323;)&#8326; + 4H&#8322;O
-<br /><a href="#Plate_44">Pl. 44</a></h3>
-<p>Usually occurs in sheaf-like
-bundles of fibrous crystals; hardness,
-5.5; specific gravity 2.2; colorless
-to white, yellow or brown; luster
-vitreous; transparent on thin edges.</p>
-<p>Stilbite crystals are really monoclinic, but on
-account of almost universal twinning, appear as
-if orthorhombic. Like the two foregoing minerals,
-stilbite is found in the seams and cavities of
-disintegrating lavas. It is readily recognized by
-its habit of forming in sheaf-like bundles of
-fibrous crystals. It may also, but more rarely,
-occur in radiating masses. In hydrochloric acid
-it is completely dissolved. It is found in lavas,
-at Weehawken and Bergen Hill, N. J., in the
-Lake Superior region, etc.</p>
-<h3 class="center"><span class="sc">Calcium</span></h3>
-<p>Calcium is one of the most abundant of metals,
-but never occurs as such in nature, nor is it used
-as a metal by man. In its metallic form it is
-yellowish-white, and intermediate between lead
-and gold in hardness. Exposed to air it soon
-tarnishes by oxidation, and in water rapidly decomposes
-the water, forming the oxide. However,
-it has a great affinity for other elements,
-and makes a large number of minerals, the most
-important of which are calcite, aragonite, gypsum
-and fluorite, while it is an essential component
-of some garnets, anorthite, epidote, amphibole
-and pyroxene. It is very widely distributed
-as limestone, and is found in solution in most all
-natural waters, and in the shells and bones of
-many animals and some plants.</p>
-<div class="pb" id="Page_144">144</div>
-<h3><a id="species_Calcite">Calcite</a>
-<br />CaCO&#8323;
-<br /><a href="#Plate_45">Pl. 45</a></h3>
-<p>Occurs in well defined crystals
-in incrustations, and in stalactitic,
-oolitic, and granular masses; hardness,
-3; specific gravity 2.7; colorless to white, or
-when impure, yellow, brown, green, red or blue;
-luster vitreous to dull; transparent on thin
-edges.</p>
-<p>Next to quartz, calcite is the most abundant of
-all minerals, and occurs in an almost endless
-variety of forms, over 300 having been described.
-It belongs to the hemihedral section of the hexagonal
-system, the form of the crystals being all
-sorts of variations of the rhombohedron, and
-combinations of left and right handed rhombohedrons.
-The cleavage is entirely uniform, in three
-directions, parallel to the faces of the rhombohedron,
-and at an angle of 74&deg; 55&prime; with each other.
-Crystals may occur in the form characteristic of
-the cleavage, but not often. The commonest
-forms are a more or less elongated scalenohedron,
-made by combining right and left handed rhombohedrons,
-so that the resulting pyramid is six-sided,
-as in figure C, <a href="#Plate_45">Plate 45</a>. Such a scalenohedron
-may be combined with other forms in a
-great variety of ways. The six-sided prism with
-the ends terminated by one or more sets of
-rhombohedral faces is also fairly common.
-Twinning occurs occasionally.</p>
-<p>The quickest way to determine calcite is by
-the hardness (3), combined with the fact that it
-effervesces, when hydrochloric acid is dropped
-upon it.</p>
-<p>An interesting feature of this mineral is its
-marked property of deflecting light rays, so that
-<span class="pb" id="Page_145">145</span>
-a line or object placed behind a piece of clear
-calcite appears double. It was with pieces of
-calcite from Iceland that this was first seen; so
-that large transparent crystals of calcite are still
-called <i>Iceland spar</i>; and such calcite is used to
-make the Nichol&rsquo;s prisms for microscopes, which
-are so useful in the study of minerals. This
-power of refracting light is present in all minerals,
-but not to such a marked degree as in calcite.
-The elongated scalenohedrons of calcite are often
-called &ldquo;dog-toothed spar&rdquo; from a fancied resemblance
-between them and the dog&rsquo;s tooth.</p>
-<p>Calcite is present in solution in the water of
-the sea and most streams, from which it is withdrawn
-by many animals and some plants, to
-make their shells, and bones. The foraminifera,
-some sponges, the echinoderms, corals and molluscs
-all draw large quantities from the water in
-which they live, and build more or less permanent
-structures from it. These shells when they fall
-to the bottom, or after being broken to bits,
-accumulate on the bottom and make limestone,
-which is widely distributed over the country.
-This same limestone, when metamorphosed and
-crystalline, is marble.</p>
-<p>Calcite then is readily soluble in water, and
-streams flowing along crevices and fissures in
-limestone dissolve out great cavities or caves,
-like the Mammoth Cave of Kentucky. Other
-water, percolating through the limestone, comes
-to these cavities saturated with lime in solution
-and drips from the roofs and walls; then as part
-of the water evaporates, it deposits part of its
-lime in icicle-like masses, hanging from the roof.
-<span class="pb" id="Page_146">146</span>
-Such masses of non-crystalline calcite are called
-<i>stalactites</i>. Below on the floor of the cave, conical
-masses are built up in the same manner where the
-dripping water falls on the floor. These are
-<i>stalagmites</i>. In these limestone caves and in
-smaller cavities many of the most beautiful
-crystals grow. Somewhat similarly, when hot
-water from deep springs comes to the surface,
-it cools and can not carry as much lime, and so
-around the spring is laid down layer after layer
-of non-crystalline calcite making a mass known
-as <i>travertine</i>. Sometimes this is colored by iron
-or other impurities and a banded effect results.
-Such travertine as the &ldquo;Suisun marble&rdquo; from
-California, &ldquo;California onyx,&rdquo; &ldquo;Mexican onyx,&rdquo;
-and &ldquo;satin spar&rdquo; all belong to this class.</p>
-<p>The coral animals, especially in tropical waters
-precipitate an enormous amount of lime, until
-whole reefs are built of lime in this non-crystalline
-form. In places it is hundreds of feet thick
-and hundreds of miles in extent. Some of this
-coral has become popular for personal adornment.
-This is particularly a small, fine-grained
-variety, <i>Corallum rubrum</i>, which lives almost
-exclusively in the Mediterranean Sea. This coral
-is red in color, varying all the way from a deep
-red to white. It grows in small masses, three
-pounds being a good sized mass, in water 60
-to 100 feet deep, requires some ten years to
-develop a full-sized mass. The making of this
-into beads and ornaments is an Italian industry.
-The demand is growing, while at the same time
-the supply is diminishing, and search is being
-widely made for more such coral, but up to the
-<span class="pb" id="Page_147">147</span>
-present time with little success. This precious
-coral is much worn as a protection against the
-&ldquo;evil eye&rdquo; and is widely imitated, apparently
-with as much protection to the wearer. When
-coral beads are offered cheap, they are probably
-something else, red gypsum being much used.
-This and all imitations can be readily detected by
-trying a drop of acid in the bead. Coral will effervesce,
-but gypsum and other substitutes will not.</p>
-<p>The bulk of the shells of most molluscs is made
-of lime, but the mother-of-pearl layer inside is
-usually aragonite. The chalk of the cliffs on
-either side of the English channel is lime, and
-composed of the shells of single celled animals.
-See <a href="#Page_213">p. 213</a>. When lime is deposited in loose porous
-masses, as around grass, etc., and below hot
-springs, this mass is termed <i>calcareous tufa</i>.</p>
-<p>Calcite will be found almost everywhere, some
-of the localities for the finest crystals being Antwerp
-and Lockport, N. Y., Middletown, Conn.,
-the caves of Kentucky, Warsaw, Ill., Joplin, Mo.,
-Hazel Green, Wis., etc.</p>
-<h3><a id="species_Aragonite">Aragonite</a>
-<br />CaCO&#8323;
-<br /><a href="#Plate_46">Pl. 46</a></h3>
-<p>Occurs in crystals, in columnar or
-fibrous masses, or incrustations;
-hardness, 3.5; specific gravity, 2.9;
-colorless, white or amber; luster vitreous; transparent
-on thin edges.</p>
-<p>Aragonite has the same chemical composition
-as calcite, but it crystallizes in the orthorhombic
-system, either in simple forms like A on <a href="#Plate_46">Plate 46</a>,
-or twinned, so as to make forms which seem hexagonal.
-When in simple crystals its form easily
-distinguishes it from calcite and dolomite, but
-<span class="pb" id="Page_148">148</span>
-when twinned it appears much like either of
-these two minerals. From calcite it can then be
-distinguished by its greater hardness and the fact
-that it has cleavage in one direction only, and
-that imperfect. The cleavage is the only easy
-method of distinguishing it from dolomite. However,
-aragonite is most always easily distinguished
-by its habits, for it generally forms long
-slender crystals, which appear more like fibers
-than crystals. Neither calcite nor dolomite is at
-all fibrous.</p>
-<p>Aragonite is much less abundant than calcite,
-and has resulted, either from deposition from hot
-waters, or from waters having sulphates in solution
-as well as lime. Much of the travertine, and
-many stalagmites and stalactites are composed
-of aragonites, forming as outlined under calcite.
-The mother-of-pearl layer in the shells of bivalves
-is generally aragonite. The pearly luster of this
-layer is due to its being formed by the successive
-deposition of one thin layer upon another; so
-that light falling on the mother-of-pearl, penetrates,
-part of it to one layer and part to another,
-and is then reflected. Certain molluscs have this
-layer composed of especially thin layers, one, the
-<i>Unios</i> or freshwater clams, the other, the &ldquo;pearl
-oysters&rdquo; or <i>Aviculid&aelig;</i>, these latter, however,
-being only distantly related to the edible oysters.
-In the cases, where molluscs of either of these two
-families are of large size, large pieces of mother-of-pearl
-can be recovered, and are used for buttons,
-handles, and various ornamental objects.
-A further peculiarity of these same molluscs is
-the formation of pearls in the sheet of flesh, lining
-<span class="pb" id="Page_149">149</span>
-the shells. The pearls are round or rounded
-concretions of aragonite. At the center there is
-a grain of sand, or more often a tiny dead parasite.
-Either was an irritant to the mollusc, and
-to be rid of it, a layer of aragonite was secreted
-around it. Then as the mollusc continued to
-grow and secrete layers for its shell, it also added
-each time another layer around the sand-grain
-or parasite, until in time a pearl of noticeable,
-and then of considerable size resulted. These
-have all the pearly luster of the mother-of-pearl
-in a sphere which tends to make the luster even
-more marked.</p>
-<p>Pearls were in use as ornaments in China some
-twenty-three centuries before Christ, and in
-India over 500 <span class="small">B.C.</span> They were very highly
-prized by the Romans and since their times the
-rulers of India have shown a remarkable fondness
-for them. Today the finest come from the
-Gulf of Persia and the Red Sea, while still
-others are found about Australia and in the
-Caribbean Sea. In the United States not a few
-are collected every year from the fresh water
-clams, some of them beautifully tinted with
-pink or yellow.</p>
-<p>Aragonite is found widely, as at Haddam,
-Conn., Edenville, N. Y., Hoboken, N. J., New
-Garden, Penn., Warsaw, Ill., etc.</p>
-<h3><a id="species_Anhydrite">Anhydrite</a>
-<br />CaSO&#8324;
-<br /><a href="#Plate_46">Pl. 46</a></h3>
-<p>Occurs in cleavable or granular
-masses, rarely in crystals; hardness,
-3-3.5; specific gravity, 2.9; color
-white, gray, bluish or reddish; luster pearly on
-cleavage faces; transparent on thin edges.</p>
-<div class="pb" id="Page_150">150</div>
-<p>When anhydrite occurs in crystals, they are
-orthorhombic, like the diagram on <a href="#Plate_46">Plate 46</a>.
-Usually, however, it is found in beds or layers,
-which were deposited by the evaporation of sea
-water, and so it is associated with salt. Anhydrite
-has three cleavage planes which are at right
-angles to one another, which produce rectangular
-or cube-like forms. Mostly anhydrite is associated
-with gypsum, from which it differs by its
-greater hardness, pseudo-cubic cleavage, and the
-fact that anhydrite is not readily soluble in acid,
-while gypsum is. Chemically it differs from gypsum
-in not having water of crystallization, which
-gypsum does have. The anhydrite is likely to
-occur as veins and irregular masses in beds of
-gypsum. Calcium sulphate is precipitated from
-sea water when 37% of the water has been evaporated,
-and it may be deposited either as anhydrite
-or as gypsum, the factors, which decide
-as to which of these two minerals it will be, being
-as yet unknown. After deposition, if exposed to
-moisture, the anhydrite may change to gypsum,
-irregular masses often remaining unchanged.</p>
-<p>It is found in salt mines in Elsworth Co., Kan.,
-in limestone cavities at Lockport, N. Y., in veins
-in Shasta Co., Calif., etc.</p>
-<h3><a id="species_Gypsum">Gypsum</a>
-<br />CaSO&#8324; + 2H&#8322;O
-<br /><a href="#Plate_47">Pl. 47</a></h3>
-<p>Occurs in crystals, in cleavable
-masses, or in fibrous masses; hardness,
-2; specific gravity, 2.3; colorless,
-white, amber, gray, or pink;
-luster vitreous, silky or pearly; transparent on
-thin edges.</p>
-<p>Gypsum crystals are monoclinic as seen on
-<span class="pb" id="Page_151">151</span>
-<a href="#Plate_47">Plate 47</a>, the perfect ones usually occurring in
-clay, as at Oxford, O., or in cavities; while crystals
-of less perfect outline, but with fine cleavages,
-are found in Utah, Kansas, and Colorado.
-The cleavage is very perfect in one direction,
-making it possible to strip off thin sheets almost
-like mica, and less perfect in two other directions,
-which appear on the smooth surface of the first
-cleavage as lines intersecting at 66&deg; 14&prime;. Twinning
-is also common in such a way, that the two
-united crystals make forms similar to arrowheads.
-These cleavages and the twinning show
-nicely in the photograph of gypsum on <a href="#Plate_47">Plate 47</a>.</p>
-<p>Gypsum is distinguished from anhydrite by its
-lesser hardness, its cleavage and by being soluble
-in acids.</p>
-<p>Most gypsum occurs in beds or granular
-masses which were deposited from evaporating
-sea-water, coming down when 37% of the water
-was lost. Such beds are often very extensive and
-are quarried as a source of gypsum to make plaster
-of Paris, stucco, neat plaster, Keene&rsquo;s cement,
-plaster and wall board, partition tiles, etc. The
-use of the gypsum for plaster of Paris and all
-these other uses is based on its affinity for water
-of crystallization. The gypsum is first heated to
-about 400&deg; C., which drives off the water of crystallization,
-and causes it to crumble to a powder,
-which is the plaster of Paris. When water is
-added, it is taken up and the powder &ldquo;sets,&rdquo; or
-recrystallizes back to gypsum. This simple
-reaction has made it very useful, for making
-moulds, casts, hard finish on walls, as stucco, etc.</p>
-<p>When the granular type of gypsum is fine
-<span class="pb" id="Page_152">152</span>
-grained, it is known as <i>alabaster</i>, which is used for
-carving vases, statuettes, ornaments, etc. The
-fibrous variety is called <i>satin spar</i>, and is sometimes
-used for cheap jewelry and ornaments, but
-it is very soft and quickly wears out. At Niagara
-Falls there is a considerable trade in objects
-carved from this satin spar, tourists buying them
-on the assumption that the mineral is native and
-comes from under the falls. Most of it, however,
-comes from Wales, the small amount of gypsum
-of that region being mostly granular.</p>
-<p>Gypsum is found all across the United States,
-as in New York, Michigan, Virginia, Ohio, Alabama,
-South Dakota, Wyoming, Colorado,
-Utah, California, etc.</p>
-<h3 class="center"><span class="sc">The Strontium Group</span></h3>
-<p>Strontium is a pale-yellow metal, ductile and
-malleable, but oxidizing quickly when exposed
-to the air. It does not occur in its native state
-in Nature, but always as some compound, usually
-either the carbonate or sulphate. It resembles
-barium, but differs in giving to the
-flame a brilliant red color, on which account the
-compounds of strontium are used mostly in
-making red fire in fireworks.</p>
-<h3><a id="species_Strontianite">Strontianite</a>
-<br />SrCO&#8323;</h3>
-<p>Occurs in needle-like crystals, or
-in columnar or fibrous masses; hardness,
-3.5-4; specific gravity, 3.6;
-color white, pale-green or pale shades of yellow;
-luster vitreous; transparent on thin edges.</p>
-<p>Strontianite is orthorhombic, but appears as
-if hexagonal, since its general habit is to have
-<span class="pb" id="Page_153">153</span>
-three twin crystals grow together in such a way
-as to make a six-sided double pyramid. In this
-it is very like witherite, both these minerals appearing
-externally much alike. They can be
-readily distinguished, however, by holding a
-piece in the flame. If it gives a red color to the
-flame it is strontianite, if green, it is witherite.
-It effervesces readily in hydrochloric acid.</p>
-<p>Strontianite is found in veins and cavities in
-limestone, where it has been deposited after
-being leached from the limestone by percolating
-waters. Though known at several localities it is
-not now being mined in this country, what we
-use being imported mostly from Germany.</p>
-<p>It is found at Schoharie, Chaumont Bay and
-Theresa, N. Y., in Mifflin Co., Penn., etc.</p>
-<h3><a id="species_Celestite">Celestite</a>
-<br />SrSO&#8324;</h3>
-<p>Occurs in crystals, cleavable
-masses and fibrous; hardness, 3;
-specific gravity, 3.9; colorless, white,
-pale-blue, or reddish; luster vitreous; transparent
-on thin edges.</p>
-<p>Celestite, the sulphate of strontium, is very like
-barite in external appearance and habit. It is
-orthorhombic and occurs in tabular crystals.
-Its cleavage is perfect on the basal plane, and
-imperfect in one other direction. The ready way
-of distinguishing celestite from barite is to hold a
-piece in the flame. If it is celestite it will color
-the flame red, if barite, green.</p>
-<p>Celestite is mostly found in veins or cavities in
-limestone, where it has been deposited by percolating
-waters, after having been leached from
-the limestone. Some years ago an important
-<span class="pb" id="Page_154">154</span>
-deposit of celestite was found on Strontian Island
-in Lake Erie, but that was soon worked out and
-now no veins are being worked in this country.
-It is also found at Chaumont Bay, Schoharie
-and Lockport, N. Y., in Kansas, Texas, West
-Virginia, Tennessee, etc.</p>
-<h3 class="center"><span class="sc">The Barium Group</span></h3>
-<p>Barium is another metal which does not occur
-in its native state in Nature. It has only been
-isolated as a yellow powder, which, exposed to
-air or water, soon changes to one of the oxides.
-Both barium and its compounds are peculiar in
-causing a green color, whenever exposed to the
-flame. Two of its compounds are fairly abundant,
-the sulphate, barite, and the carbonate,
-witherite. The former is the more abundant and
-has come to be fairly widely used, something
-over 100,000 tons being annually consumed in the
-United States, to make the body in flat finish
-paints for interior work and light colors, for a
-filler in rubber goods, linoleum, oil cloth, glazed paper,
-and for a wide range of chemical compounds.</p>
-<h3><a id="species_Barite">Barite</a>
-<br />BaSO&#8324;
-<br /><a href="#Plate_48">Pl. 48</a>
-<br /><i>heavy spar</i></h3>
-<p>Occurs in crystals or in lamellar,
-nodular or granular masses; hardness
-3; specific gravity, 4.5; colorless,
-white or almost any color; luster
-vitreous; transparent on thin edges.</p>
-<p>Barite occurs in orthorhombic crystals, which
-are tabular in form, and usually have the edges
-beveled, as in figure A, <a href="#Plate_48">Plate 48</a>. There is cleavage
-in three directions, a rather perfect basal
-cleavage, and two less perfect cleavages, which
-<span class="pb" id="Page_155">155</span>
-are at right angles to the basal cleavage plane,
-and intersect each other at 78&deg;.</p>
-<p>The tabular form, the cleavage, the heavy
-weight, and the fact that a piece of barite put
-into the flame colors it green, all serve to distinguish
-this mineral.</p>
-<p>Barite is a secondary mineral of aqueous origin,
-which has been deposited in veins and cavities
-in igneous, metamorphic, or sometimes sedimentary
-rocks. It is most likely to occur in
-veins in igneous or metamorphic rocks, the
-barium having been dissolved from certain feldspars
-and micas by percolating water, and then
-redeposited in the fissures, as the water came into
-them. If in sedimentary rocks, the barite veins
-are usually in limestones. Barite is quite likely
-to be a gangue mineral for the ores of lead.</p>
-<p>It is found at Hatfield and Leverett, Mass.,
-Cheshire, Conn., Pillar Point, N. Y., Cartersville,
-Ga., in Virginia, North Carolina, South
-Carolina, Missouri, Kentucky, Tennessee, Alabama,
-Illinois, Wisconsin, Nevada, California,
-Alaska, etc.</p>
-<h3><a id="species_Witherite">Witherite</a>
-<br />BaCO&#8323;
-<br /><a href="#Plate_48">Pl. 48</a></h3>
-<p>Occurs in crystals, or in granular
-or columnar masses; hardness, 3.5;
-specific gravity, 4.3; color white to
-gray; luster vitreous; translucent on thin edges.</p>
-<p>Witherite is not an abundant mineral. Its
-crystals are really orthorhombic, but they are
-usually twinned, three crystals growing through
-each other in such a manner that the resulting
-crystal appears like a six-sided double pyramid,
-similar to the one figured on <a href="#Plate_48">Plate 48</a>. The commonest
-<span class="pb" id="Page_156">156</span>
-mode of occurrence is in compact
-masses. Witherite effervesces when cold acid is
-dropped upon it, which, with its heavy weight,
-and the green color it gives to the flame, serves
-to distinguish the mineral. It is used for medicines,
-in chemical industries, and a considerable
-amount is made into rat poisons. The chief
-locality for witherite is in northern England,
-but in this country it is found along with barite,
-especially at Lexington, Ky., and in Michigan.</p>
-<h3 class="center"><span class="sc">Carbon</span></h3>
-<p>Carbon is an element widely distributed in
-nature, occasionally appearing in its elementary
-form, as graphite or the diamond, but much more
-important in its compounds. Small quantities
-are present in the air as carbon dioxide, CO&#8322;, immense
-quantities occurring in the carbonate
-minerals, which have been considered under their
-respective metallic salts, as calcite, malachite,
-siderite, cerrusite, smithsonite, witherite, etc.,
-and still other large quantities being represented
-in organic compounds, which occur as rocks
-under the heads of petroleum, coal, etc. The
-occurrence of limestones, graphite, coal or petroleum
-is always indicative of the activity of living
-organisms, and in some cases is the only indication
-of life in the earlier rocks.</p>
-<h3><a id="species_Graphite">Graphite</a>
-<br />C
-<br /><i>Plumbago</i></h3>
-<p>Occurs in hexagonal scales or
-flakes, in layered masses, or earthy
-lumps; hardness, 1; specific gravity,
-2.1; color black or steel-gray; streak gray; luster
-metallic; opaque on thin edges.</p>
-<div class="pb" id="Page_157">157</div>
-<p>Like the diamond graphite is pure carbon, but
-in this case it is in non-crystalline form. It
-occurs in both igneous and metamorphic rocks.
-In the former case it is either in flakes in the rock,
-or in veins, and has been derived directly from
-the molten magmas, having either precipitated
-in the hardening granite or lava, or having been
-carried into the fissures and there precipitated
-to make the veins of graphite. In either case
-the graphite probably represents organic deposits
-which have been melted into the igneous magma
-at the time of its formation. Graphite may also
-occur in metamorphic rocks, beds of coal or other
-organic deposits being altered by the heat. Such
-beds are often of considerable extent and economic
-importance.</p>
-<p>The extreme softness, greasy feel, and the
-dark-gray streak readily distinguish graphite.</p>
-<p>It is widely used in making crucibles and furnace
-linings for foundries, lead pencils, paint,
-lubricating powders, etc.</p>
-<p>Graphite is found at Brandon, Vt., Sturbridge,
-Mass., Ashford, Conn., in Essex, Warren and
-Washington Cos., N. Y., Clay, Chilton and
-Coosa Cos., Ala., Raton, N. M., Dillon, Mont.,
-etc.</p>
-<h3><a id="species_Diamond">Diamond</a>
-<br />C</h3>
-<p>Occurs in octahedral crystals;
-hardness, 10; specific gravity, 3.5;
-colorless to yellow, brown, blue, etc.,
-luster adamantine; transparent on thin edges.</p>
-<p>Like graphite the diamond is pure carbon, but
-in this case in crystal form. It is the hardest of
-all minerals, and as brilliant as any; so that in
-<span class="pb" id="Page_158">158</span>
-spite of being by no means the rarest, it may
-easily be considered the most popular of all gems.
-Tiny diamonds have been made artificially under
-great heat and pressure; so that this mineral is
-thought of as forming in Nature in dark igneous
-lavas at great depths. The diamond has good
-cleavage parallel to the octahedron faces, and,
-in spite of some traditions to the contrary, is
-brittle.</p>
-<p>There are not many diamond localities, the
-most famous being the Kimberley district of
-South Africa, which produces many times as
-many diamonds as all the others put together,
-though all the time some are being found in
-Borneo and Brazil. A very few have been found
-in the United States, only one locality however
-yielding them in the original matrix. That is at
-Murfreesboro, Ark., where they are mined in a
-disintegrating peridotite (a dark lava, mostly
-peridot), which has been extruded through the
-sedimentary rocks of that region. This matrix
-is similar to the &ldquo;blue earth,&rdquo; the matrix of the
-diamonds of South Africa, which occurs in
-&ldquo;pipes,&rdquo; representing the necks of ancient volcanoes.
-The American diamonds are of small
-size, averaging considerably less than a third of
-a carat in weight, which does not allow great
-value to the individual diamonds.</p>
-<p>From time to time, especially large diamonds
-have been found in different parts of the world,
-the largest being the Cullinan diamond, found
-at the Premier Diamond Mine of South Africa.
-It weighed 3025 carats or about a pound and a
-quarter, and was valued at over $3,000,000. It
-<span class="pb" id="Page_159">159</span>
-was presented to King Edward VII, who had it
-cut into 11 brilliants, four of which are larger
-than any other diamond yet found. Other famous
-diamonds, like the Kohinoor, 106 carats,
-found in India in 1304; the Regent, 136 carats,
-also found in India; the Orloff, 193 carats, set in
-the eye of an Indian idol; the South Star, 125
-carats, the largest ever found in Brazil; the blue
-Hope, etc., have in many cases romantic and
-interesting stories woven about them.</p>
-<p>Though for ages diamonds have been highly
-prized gems, it is only in comparatively recent
-times that cutting and polishing have been resorted
-to, for the purpose of enhancing their
-brilliancy. This is done by grinding reflecting
-faces on the original stone, by the aid of discs of
-iron or tin in which diamond dust has been embedded.
-Diamond chips and cloudy or imperfect
-diamonds are used for making tools for cutting
-glass, rock drills, etc.</p>
-<h3 class="center"><span class="sc">Phosphorus</span></h3>
-<p>The element phosphorus at ordinary temperatures
-is an almost colorless, faintly yellow, solid
-substance of glistening appearance and waxy
-consistency. In Nature it does not occur pure,
-but always as one of its compounds. It is of
-great importance to man for it is one of the essentials
-for plant growth and also for the higher
-animals, being required for the bones and to some
-extent for nervous tissue. Originally it is found
-in all the igneous rocks. Some of the phosphorus
-is removed by solution and carried to other regions
-<span class="pb" id="Page_160">160</span>
-and to the sea. From this distribution it
-comes into the sedimentary rocks, and, when
-they are altered by heat, into the metamorphic
-rocks. Thus it has a wide, though by no means
-even, distribution. The soils formed by disintegration
-of these rocks probably all have some
-phosphorus in them; but where there is vigorous
-plant growth, it soon tends to become exhausted,
-and must be renewed. For this reason the use of
-phosphates has become of prime importance in
-Agriculture. The possession of beds of rock
-carrying phosphorus has come to be of international
-importance. The United States is particularly
-fortunate in this respect, and produces
-over 25% of the world&rsquo;s supply of phosphates.
-Most all the phosphorus is recovered either
-from phosphate minerals, the most important
-of which is apatite, or from the non-crystalline
-and impure mixtures of phosphate minerals
-and other substances, discussed under phosphate
-rock.</p>
-<h3><a id="species_Apatite">Apatite</a>
-<br />Ca&#8325;F(PO&#8324;)&#8323;
-<br /><a href="#Plate_49">Pl. 49</a></h3>
-<p>Occurs in crystals, concretionary
-nodules, or in bedded masses; hardness,
-5; specific gravity, 3.2; color
-reddish-brown or green, rarely white or colorless;
-luster vitreous; translucent on thin
-edges.</p>
-<p>Apatite occurs in hexagonal prisms, usually
-with the ends truncated by a basal plane, and
-with one or more sets of pyramidal faces between
-the prism and the basal plane. Crystals range in
-size from tiny to over a foot in diameter. There
-is but one cleavage and that is basal. The crystal
-<span class="pb" id="Page_161">161</span>
-form, cleavage, and hardness will easily
-determine this mineral. Apatite is usually associated
-with igneous or highly metamorphic
-rocks, such as granites, gneisses, and crystalline
-limestones. While the phosphoric acid of apatite
-is highly desirable for use in fertilizers, the crystals
-do not occur in sufficient abundance to
-make them commercially available, and non-crystalline
-phosphate rocks are resorted to for
-this purpose.</p>
-<p>Crystals of apatite are found at Norwich and
-Bolton, Mass., Rossie and Edenville, N. Y.,
-Suckasunny and Hurdstown, N. J., Leiperville,
-Penn., Wilmington, Del., etc. Templeton, Canada,
-is perhaps the best known locality for fine
-apatite.</p>
-<h3><a id="species_Turquois">Turquois</a>
-<br />H&#8325;[Al(OH)&#8322;]Cu(OH)(PO&#8324;)&#8324;</h3>
-<p>Occurs in seams and incrustations;
-hardness, 6; specific gravity,
-2.7; color bluish-green; streak blue;
-luster waxy; translucent to opaque on thin
-edges.</p>
-<p>In this country this complex phosphate of
-aluminum and copper is found in streaks and
-patches in volcanic rocks, but in Persia comes
-from metamorphic rocks. To the Persians it was
-a magical stone, protecting the wearer from injuries,
-and among the Pueblo Indians it was
-regarded as of religious value in warding off evil.
-The best turquois comes from Persia, but it has
-been found at several points in the United States,
-as in Los Cerrillos and Burro Mts., N. M., in
-Mohave Co., Ariz., San Bernardino Co., Cal.,
-in Nevada and Colorado.</p>
-<div class="pb" id="Page_162">162</div>
-<h3 class="center"><span class="sc">Fluorine</span></h3>
-<p>At ordinary temperatures the element fluorine
-is a colorless gas, which was not obtained pure
-until 1888, because it could not be contained in
-vessels of glass, gold, platinum, etc. At that
-time it was made and kept in a vessel composed
-of an alloy of platinum and iridium. Its most
-important compound is hydrofluoric acid, a fuming
-liquid, which is mostly used to etch or dissolve
-glass. It occurs in several minerals, like
-tourmaline, turquois, etc., but the only one used
-to obtain the hydrofluoric acid is fluorite.</p>
-<h3><a id="species_Fluorite">Fluorite</a>
-<br />CaF&#8322;
-<br /><a href="#Plate_50">Pl. 50</a>
-<br /><i>Fluor spar</i></h3>
-<p>Occurs in crystals and cleavable
-masses; hardness, 4; specific gravity,
-3.2; colorless or some shade of violet,
-green, yellow, or rose; luster vitreous; transparent
-on thin edges.</p>
-<p>Fluorite usually occurs in beautiful cubic
-crystals, often with the edges and corners beveled
-by smaller faces, and occasionally in twins,
-which seem to have grown through each other.
-There is perfect cleavage parallel to each of the
-octahedral faces, which often, as in the illustration
-on <a href="#Plate_50">Plate 50</a>, show as cracks cutting off the
-corners.</p>
-<p>Since fluorite loses weight and color on heating,
-it is concluded that the colors are due to the
-presence of hydrocarbon compounds. The red
-and the green fluorite when heated to above
-212&deg; F. become phosphorescent, as may be seen
-if they are thus heated and exposed to the light,
-then taken into the dark.</p>
-<p>Fluorite is quite commonly the gangue mineral
-<span class="pb" id="Page_163">163</span>
-associated with metallic ores, and is also likely
-to occur with topaz, apatite, etc. It is generally
-in such places that it seems to have been deposited
-from hot vapors, rising from igneous
-magmas.</p>
-<p>It is the only mineral at all common from
-which fluorine can be obtained, and is used for
-making hydrofluoric acid, and other chemical
-compounds of this element. It is, however, of
-much greater importance as a flux in reducing
-iron, silver, lead and copper ores. In the industries
-it finds a place, being used to make apochromatic
-lenses, cheap jewelry, and for the
-electrodes in flaming arc lamps.</p>
-<p>Fluorite is widely distributed, some of the
-better known localities being Trumbull and Plymouth,
-Conn., Rossie and Muscalonge Lake,
-N. Y., Gallatin Co., Ill., Thunder Bay, Lake
-Superior, Missouri, etc.</p>
-<h3><a id="species_Halite">Halite</a>
-<br />NaCl
-<br /><a href="#Plate_50">Pl. 50</a>
-<br /><i>Salt</i></h3>
-<p>Occurs in crystals, and in cleavable
-and granular masses; hardness,
-2.5; specific gravity, 2.1; colorless to
-white; luster vitreous; transparent on thin edges.</p>
-<p>Halite is common salt, occurring in cubic
-crystals, with perfect cubic cleavage. Its form,
-hardness, taste, and solubility in water make it
-easy to determine.</p>
-<p>Halite is the most abundant salt in sea water,
-making about 2.5% out of the total of 3.5% of
-solids in solution. It is also a prominent, when
-not the leading, salt in solution in the waters of
-inland lakes, like Great Salt Lake, or the Dead
-Sea, there being 20% of halite in the former and
-<span class="pb" id="Page_164">164</span>
-8% in the latter, though the total of solid in
-solution in the water of the Dead Sea is greater
-than that in Great Salt Lake.</p>
-<p>The great salt deposits are mostly the result of
-the evaporation of the water of arms or isolated
-portions of former oceans; the salt, gypsum, etc.,
-left by the drying sea, having been buried beneath
-later sediments. Other bodies of salt represent
-the disappearance of ancient lakes.
-There are also the curious &ldquo;salt domes&rdquo; of
-Louisiana and Texas, which are immense, roughly
-circular, subterranean masses of salt extending to
-as yet unknown depths which are thought to have
-been formed by masses of salt from some deep
-source bed pushing their way upward through the
-overlying formations by plastic flowage. As the
-upthrust took place the sediments were arched
-into domes. Some of these domes are today important
-sources of rock salt.</p>
-<p>There are extensive beds of salt under parts of
-New York, Michigan, Ohio, Oklahoma, Kansas,
-etc., which are mostly worked by drilling wells
-into the salt layer, then introducing hot water to
-dissolve the salt. The brine thus formed is
-pumped to the surface, and the salt recovered by
-evaporation in pans. During the process, skeleton
-crystals of salt with concave faces may form,
-but in Nature the crystals are uniformly solid
-cubes.</p>
-<h3><a id="species_Boracite">Boracite</a>
-<br />Mg&#8327;Cl&#8322;B&#8321;&#8326;O&#8323;&#8320;</h3>
-<p>Occurs in small crystals or granular
-masses; hardness of crystals, 7;
-of the masses, 4.5; specific gravity
-3; colorless to white; luster vitreous; transparent
-to translucent on thin edges.</p>
-<div class="pb" id="Page_165">165</div>
-<p>Small crystals, associated with salt and gypsum,
-occur in the beds and incrustations, which
-result from the drying up of alkaline lakes,
-especially in Nevada and southern California.
-The crystals are orthorhombic, but appear like
-perfect cubes, with the edges beveled and part of
-the corners cut. They are not easily dissolved in
-water, but quickly go into solution in hydrochloric
-acid.</p>
-<h3><a id="species_Colemanite">Colemanite</a>
-<br />Ca&#8322;B&#8326;O&#8321;&#8321; + 5H&#8322;O</h3>
-<p>Occurs in crystals or compact
-masses; hardness, 4.5; specific gravity,
-2.4; colorless to white; luster
-vitreous; translucent on thin edges.</p>
-<p>The crystals when they occur, are monoclinic;
-but usually colemanite is a bedded deposit,
-which has resulted from the drying up of a saline
-lake. It was first found in Death Valley, Cal.,
-in 1882, then near Daggett, Cal., and since then in
-several similar locations in Nevada and Oregon.
-The deposits are of all grades of purity, the colemanite
-being mixed with varying quantities of
-mud. Today this mineral is the chief source of
-borax, which is used in medicines, cosmetics,
-colored glazes, enamel, and as a preservative.</p>
-<h3><a id="species_Borax">Borax</a>
-<br />NaB&#8324;O&#8327; + 10H&#8322;O</h3>
-<p>Occurs in crystals or in powdery
-incrustations; hardness, 2; specific
-gravity, 1.7; colorless to white;
-luster vitreous; translucent on thin edges.</p>
-<p>The crystals are tiny and monoclinic, this
-mineral being usually obtained by the evaporation
-of the saline waters of such lakes as Clear and
-Borax Lakes in southern California, or from the
-muds of salt marshes, like Searles Borax Marsh
-<span class="pb" id="Page_166">166</span>
-in California. Originally most of our borax
-came from a large saline lake in Tibet, but now
-most of it is obtained from colemanite. Borax is
-soluble in water, giving it a sweetish taste.</p>
-<h3><a id="species_Sulphur">Sulphur</a>
-<br />S
-<br /><a href="#Plate_51">Pl. 51</a></h3>
-<p>Occurs in crystals, incrustations or
-compact masses; hardness, 2; specific
-gravity, 2; color yellow; streak
-yellow; luster resinous; translucent on thin edges.</p>
-<p>Aside from the numerous compounds, such as
-the sulphides of the metals like pyrite, galena,
-sphalerite, etc., and the sulphates, like gypsum,
-barite, anglesite, etc., sulphur occurs in its elemental
-form in Nature. In this case it may be in
-crystals, which are orthorhombic and usually
-occur as octahedrons, with the upper and lower
-ends truncated, either by a basal plane, or by a
-lower octahedron, or by both. Incrustations and
-compact masses are, however, much the commoner
-mode of occurrence. The incrustations
-are found mostly about volcanic regions, where
-the sulphur has risen from the molten lavas as a
-sublimate, and on cooling has been deposited
-in crevices or on the adjacent surfaces. Irregular
-masses of sulphur are often found where sulphide
-minerals, like pyrite or galena have been decomposed
-in such a way as to leave the sulphur
-behind. The extensive beds of sulphur are usually
-associated with gypsum, and are thought to
-be the result of water, containing bituminous
-matter, so acting on gypsum as to remove the
-calcium and oxygen as lime, and leave the
-sulphur. Finally many waters carry sulphates
-in solution, from which the sulphur may be
-<span class="pb" id="Page_167">167</span>
-precipitated by certain sulphur bacteria, making
-thus incrustations on the bottom of ponds or lakes.</p>
-<p>Sulphur is used for making matches, gunpowder,
-fireworks, insecticides, in medicine, vulcanizing
-rubber, etc. It is widely distributed,
-however, most of the present world&rsquo;s production
-is from deposits associated with the &ldquo;salt domes&rdquo;
-of Texas and Louisiana. A &ldquo;caprock&rdquo; of gypsum
-and anhydrite overlies many of these which often
-contains elemental sulphur. Wells are drilled into
-this, and the sulphur is melted by the introduction
-of hot steam. This melted sulphur is then pumped
-to the surface and run into molds.</p>
-<p>Some of the best known localities are Sulphurdale,
-Utah, Cody and Thermopolis, Wyo., Santa
-Barbara Co., Cal., Humboldt Co., Nev., and about
-the hot springs of the Yellowstone Park.</p>
-<h3><a id="species_Ice">Ice</a>
-<br />H&#8322;O
-<br /><a href="#Plate_51">Pl. 51</a>
-<br /><i>water</i></h3>
-<p>Occurs solid as ice, snow and frost,
-or liquid as water; hardness, 2;
-specific gravity, .92; colorless to
-white; luster adamantine; transparent on thin
-edges.</p>
-<p>Though we seldom think of ice, and its liquid
-form, water, as a mineral, still it is one, and
-perhaps the most important of all minerals, as
-well as the most common. Ice melts at 32&deg; F.
-and vaporizes at 212&deg; F., being then termed
-steam. Because it is so common and liquid at
-ordinary temperatures it acts as a solvent for a
-host of other minerals, and is therefore the agent
-by which they are transported from place to
-place and redeposited in veins and beds.</p>
-<div class="pb" id="Page_168">168</div>
-<p>Not only does water act as a transportation
-agent for minerals in solution, but is also the
-agent of erosion and weathering. Water vaporizes
-slowly when exposed to the air at all temperatures
-above freezing, and so it is slowly rising
-from the surface of the sea or lakes or moist
-ground into the air, where it would accumulate
-until the air was saturated, if the air would only
-keep still and at a uniform temperature. The air
-will hold a given amount of water vapor, which
-is, for example, 17 grams per cubic meter when
-the temperature is 68&deg; F., but at 59&deg; F. it will
-hold only 12&frac12; grams, or at 50&deg; F. only 9 grams.
-Thus the air is more or less completely saturated
-at higher temperatures, and when the temperature
-is lowered the air can not hold all it has
-taken up, and it is precipitated in dew, rain or
-snow, most often as rain. When the rain falls it
-mechanically carries away, and more or less
-slowly transports to other places particles of
-rock, being thus the agent of erosion; and when it
-is slowed down, as on entering the quiet water of
-a lake or the sea, it drops the mechanically carried
-sediment and makes sedimentary deposits.</p>
-<p>Another very important and unique feature of
-water is that on freezing it expands about &sup1;/&#8321;&#8321;th of
-its former bulk, so that, as a result, ice floats,
-and also wherever water in crevices is frozen, the
-crevices are enlarged. In locations where this
-freezing and melting take place repeatedly
-throughout a year, there the breaking up of
-rocks is rapid.</p>
-<p>This is hardly the place to take up a complete
-discussion of water, but its action as a solvent,
-<span class="pb" id="Page_169">169</span>
-mechanically, and in freezing, melting, and
-vaporizing is the basis of a large part of the
-study of geology.</p>
-<p>When water crystallizes, as in forming ice, it is
-in the hexagonal system. It tends to twinning
-and a snow-flake is made up of a large number of
-twinned crystals, each diverging from the other
-at 60&deg;. When ice is formed in the air or on the
-surface of water it forms these complex and
-beautiful multiple twins, of which but a couple
-are suggested here. Beneath the surface the
-hexagonal crystals grow downward into the
-water, parallel to each other, making a fibrous
-structure, which is very apparent when ice is
-&ldquo;rotten,&rdquo; which is the time at which the surfaces
-of the prisms are separating, because the molecules
-leave the crystal in the reverse order to
-which they united with it. Frost in marshy or
-spongy ground will often show this fibrous growth
-beautifully.</p>
-<div class="pb" id="Page_170">170</div>
-<h2 id="c5"><span class="h2line1">CHAPTER IV</span>
-<br /><span class="h2line2">THE ROCKS</span></h2>
-<p>Broadly speaking a rock is an essential part
-of the crust of the earth, and includes loose material,
-like sand, mud, or volcanic ashes, as well
-as compact and solid masses, like sandstone and
-granite. Rocks are aggregates of minerals,
-either several minerals grouped together, as are
-mica, quartz and feldspar to make granite, or
-large quantities of a single mineral, like quartz
-grains to make sandstone.</p>
-<p>The rocks are most conveniently classified
-according to their mode of origin, into three main
-groups, igneous, sedimentary, and metamorphic.
-The igneous rocks are those which have solidified
-from a molten magma, like lavas, granites, etc.
-The sedimentary rocks are those which represent
-accumulations of fragments or grains, derived
-from various sources, usually the weathering
-of other rocks, and deposited by such agents
-as water, wind and organisms. Metamorphic
-rocks are those which were originally either igneous
-or sedimentary, but have been altered
-by the actions of heat, pressure and water, so
-that the primary character has been changed,
-often to such an extent as to be obscured.</p>
-<p>Rocks once formed in any of the above ways
-are being constantly altered in character by the
-<span class="pb" id="Page_171">171</span>
-various processes of nature. Those exposed on
-the surface are weathered to pieces, and the fragments
-are transported by wind or water to accumulate
-elsewhere as sedimentary rocks. Those
-buried deep beneath the surface are affected by
-the high temperature and pressure of the depths
-of the earth and thus metamorphosed. For instance
-a granite exposed on the surface is slowly
-weathered, some parts being carried away in
-solution by the rain water, others less soluble
-remaining as grains of quartz, mica or kaolin.
-These are transported by water and sorted, the
-finer kaolin being carried to still and deep water,
-the quartz and mica accumulating in some lowland
-as sand. This sand will in time be cemented
-to a sandstone, later slowly buried beneath the
-surface. If buried deep it will feel the effect
-of the interior temperature, which increases as
-one goes down at the rate of one degree F. for
-every 50 feet. If this should be in a region where
-folding and mountain-making takes place, the
-material under the folds would be melted (because
-of the relief from pressure which would
-permit the high temperature to act freely) and
-become igneous rock, either coming to the surface
-as lava, or remaining below the surface and
-making a granite or similar rock; while the
-sedimentary material not melted but near
-enough to the molten material to be affected,
-would be metamorphosed, in this case to a quartzite.
-Much of the interest and profit in studying
-rocks, will come from the understanding which
-they will give as to the history of that particular
-part of the earth&rsquo;s crust where they are found.</p>
-<div class="pb" id="Page_172">172</div>
-<h3 class="center"><span class="sc">Igneous Rocks</span></h3>
-<p>Igneous rocks are those which have formed
-from material that has been melted, which involves
-temperatures around 1300&deg; C.; or, if
-there is water in the original material, temperatures
-as low as 800&deg; C. will suffice. Considering
-the increase of temperature to be a degree for
-every 50 feet downward, this involves the rocks
-having been at depths of 5 to 10 miles below the
-surface. While at such depths the temperature
-must be high enough to melt rocks, the great
-pressure of the overlying rocks seems to keep
-them solid; for we know that the center of the
-earth is solid, as is shown by a variety of observations,
-such as the rate at which earthquake waves
-are transmitted through the earth, the lack of
-tidal effects, etc. However, there is every reason
-to believe that if the pressure is removed from
-the rocks which are five to ten miles below the
-surface, there is heat enough at those depths to
-melt them. When the crust of the earth is
-folded, as when mountain ranges are formed, the
-areas under the arches or upward folds are relieved
-of pressure. Then those rocks, which are
-under the arches and are relieved, become molten.
-The molten magma may well up and fill the
-space beneath the arch where it would cool again
-very slowly; or, if there is fissuring during the
-folding, some of the molten material may be
-forced out through the fissures and pour out over
-the surface as lava. Another area in which pressures
-may be locally relieved is in the region of
-faulting, where the crust of the earth is broken
-<span class="pb" id="Page_173">173</span>
-into blocks, between which there are readjustments,
-some being tipped one way, some another,
-some uplifted. Here again there would be areas
-of relieved pressure and molten magmas would
-form, some of them solidifying in place, others
-rising to the surface.</p>
-<p>The molten material is termed the <b>magma</b>,
-and when it reaches the surface, great quantities
-of water vapor and other gases escape: or these
-gases may even escape from magmas which do
-not reach the surface, rising through fissures.
-As these hot vapors pass through the fissures,
-they are cooled, and may deposit part or all of
-their dissolved compounds in the fissure, making
-veins. <b>Lava</b> is the magma minus the vapors.
-Magmas vary greatly from place to place, indicating
-that they are formed locally and do not
-come from any general interior reservoir, as has
-sometimes been suggested.</p>
-<p>When the molten magmas escape to the surface,
-they are termed <b>extrusive</b>, and as they
-spread out in a layer this is termed a <b>sheet</b>. This
-rise and overflow may be quiet, and from time
-to time one outpouring may follow another making
-sheet after sheet. Or after one outpouring,
-the pressure below may cease for a time and
-allow the lava to solidify and make a cap or
-cover over the opening. Before more lava can
-rise, this cover must be removed. This usually
-happens in an explosive manner, the lava below,
-with the increasing pressure exerted by its expanding
-gases, finally exerting enough pressure,
-so that the cover is broken, or shattered and
-thrown in thousands of fragments into the air,
-<span class="pb" id="Page_174">174</span>
-as happened at Mt. Pel&eacute;e on the Island of Martinique
-in 1902. The fragments thrown into the
-air are often termed volcanic ashes, though this
-is not a good word for them, for they have not
-been burned.</p>
-<p>In case the molten magmas under the relieved
-areas do not reach the surface they are termed
-<b>intrusive</b>. Such magmas may remain in the
-space under a mountain fold, or be forced in
-fissures part way to the surface. When the magma
-is forced into more or less vertical cracks and
-there solidifies, and these are exposed by erosion,
-they are termed <b>dikes</b>. Sometimes the magmas
-have risen part way to the surface and then
-pushed their way between two horizontal layers
-of rock and there hardened, in which case they
-are termed <b>sills</b>, when uncovered. The Palisades
-along the Hudson River are the exposed edge of
-a sill. Again the molten magmas may well up
-and spread between two horizontal layers, but
-come faster than they can spread horizontally,
-and then the magma takes the form of a half
-sphere, and the overlying layers of rock are
-domed up over it. Such a mass is termed a
-<b>laccolith</b>. In all these cases the mass of igneous
-rock is only discovered when the overlying rocks
-have been eroded off. The great mass of molten
-magma under the arches of mountain ranges simply
-cools slowly into a granitic type of rock.
-These masses are exposed when the thousands of
-feet of overlying rock are eroded off. When
-these masses are exposed, if of but a few miles in
-extent, they are called stocks, but, if of many
-miles in length and breadth, they are <b>batholiths</b>,
-<span class="pb" id="Page_175">175</span>
-and are very characteristic of the heart of
-mountain ranges.</p>
-<p>In all the above cases the exterior of the molten
-mass cools first, and forms a shell around the
-rest. The shell determines the size of the mass.
-As the cooling continues into the interior, it also
-solidifies, and as all rocks shrink on cooling,
-cracks develop, separating the mass into smaller
-pieces. There is usually no regularity about
-these cracks and the mass is divided into blocks
-from six inches to three feet in diameter. However,
-in some cases, especially in sills and laccoliths
-where the cooling is slower, the shrinkage
-may be marked by a regular system of cracks
-which bound the rock into more or less regular
-hexagonal columns. The Palisades and the
-Devil&rsquo;s Tower in Wyoming (See <a href="#Plate_52">Plate 52</a>) show
-this structure. The Devil&rsquo;s Tower is the remnant
-of a laccolith, all except the central core of
-which has been eroded away. All of the above
-terms have nothing to do with composition, but
-refer entirely to the manner of occurrence.</p>
-<p>While the igneous rocks are classified according
-to their composition, the rate at which they
-cooled has much to do with their texture, and
-certain names apply to the texture. For instance
-when the molten lava cools very rapidly, there is
-no time for the formation of crystals, and the
-resulting rock is glassy or non-crystalline. If the
-cooling is slow as in large bodies, crystals have
-time to form and grow to considerable size as
-in granites. Between these all grades may occur;
-and one classification of igneous rocks expresses
-their rate of cooling, in such terms as the following.</p>
-<div class="pb" id="Page_176">176</div>
-<p><b>Glassy</b>&mdash;lavas which have cooled so quickly
-that they are without distinct crystallization,
-such as obsidian, pitchstone, etc.</p>
-<p><b>Dense or felsitic</b>&mdash;lavas which have cooled less
-rapidly, so that crystals have formed, but in
-which the crystals are too small to be identified
-by the unaided eye, such as felsite or basalt.</p>
-<p><b>Porphyritic</b>&mdash;magmas from which, in solidifying,
-one mineral has crystallized out first and the
-crystals have grown to considerable size, while
-the rest have remained small.</p>
-<p><b>Granitoid</b>&mdash;magmas which have solidified
-slowly, so that all the minerals have crystallized
-completely, and the component crystals are large
-enough to be recognized readily, as in granite.</p>
-<p><b>Fragmental</b>&mdash;a term applied to the fragments
-which have resulted from explosive eruptions
-of igneous rocks. These fragments may be loose
-or consolidated. Volcanic ashes are typical.</p>
-<p><b>Porous</b>&mdash;a term applied to the lava near the
-upper surface, which is filled with gas cavities,
-such as pumice.</p>
-<p><b>Amygdoloidal</b>&mdash;is the term applied to porous
-lavas, when the cavities have been filled by other
-minerals, such as calcite or some of the zeolites.</p>
-<p class="tb">In determining a rock, first decide whether it
-is igneous, sedimentary or metamorphic. The
-igneous character is recognized by its being either
-glassy, or composed of masses of crystals irregularly
-arranged, there being neither layering nor
-bedding.</p>
-<div class="pb" id="Page_177">177</div>
-<h4>CLASSIFICATION OF IGNEOUS ROCKS</h4>
-<table class="border" summary="">
-<tr class="th"><th><span class="sc">Texture</span> </th><th colspan="4">Excess of light colored minerals </th><th colspan="4">Excess of dark colored minerals</th></tr>
-<tr><td class="l">Glassy </td><td colspan="4" class="l"><a href="#species_Obsidian">obsidian</a>, <a href="#species_Perlite">perlite</a>, <a href="#species_Scoria">pumice</a>, <a href="#species_Pitchstone">pitchstone</a> </td><td colspan="4" class="l"><a href="#species_Scoria">scorias</a>, <a href="#species_Trachite">trachylyte</a>, <a href="#species_Obsidian">basalt-obsidian</a></td></tr>
-<tr class="th"><th> </th><th colspan="2">Feldspar orthoclase </th><th colspan="4">Feldspar Plagioclase </th><th colspan="2">No feldspar</th></tr>
-<tr class="th"><th> </th><th colspan="2">Mica and/or hornblende and/or augite </th><th colspan="2">Mica and/or hornblende </th><th colspan="2">with pyroxene </th><th colspan="2">augite and/or hornblende and/or mica</th></tr>
-<tr class="th"><th> </th><th>+quartz </th><th>-quartz </th><th>+quartz </th><th>-quartz </th><th>+olivine </th><th>-olivine </th><th>+olivine </th><th>-olivine</th></tr>
-<tr><td class="l">Dense </td><td class="l"><a href="#species_Rhyolite">rhyolite</a> </td><td class="l"><a href="#species_Trachite">trachite</a> </td><td class="l"><a href="#species_Dacite">dacite</a> (felsite) </td><td class="l"><a href="#species_Andesite">andesite</a> (felsite) </td><td class="l"><a href="#species_Basalt">basalt</a> </td><td class="l"> </td><td class="l"> </td><td class="l"><a href="#species_Pyroxenite">augitite</a> or <a href="#species_Hornblende">hornblendite</a></td></tr>
-<tr><td class="l">Porphyritic </td><td class="l"><a href="#species_Porphyry">rhyolite-porphyry</a> </td><td class="l"><a href="#species_Porphyry">trachite-porphyry</a> </td><td class="l"><a href="#species_Porphyry">dacite-porphyry</a> </td><td class="l"><a href="#species_Porphyry">andesite-porphyry</a> </td><td class="l"><a href="#species_Porphyry">basalt-porphyry</a> </td><td class="l"> </td><td class="l"> </td><td class="l"><a href="#species_Porphyry">augitite-porphyry</a></td></tr>
-<tr><td class="l">Granitoid </td><td class="l"><a href="#species_Granite">granite</a> </td><td class="l"><a href="#species_Syenite">syenite</a> </td><td class="l"><a href="#species_QuartzDiorite">quartz-diorite</a> </td><td class="l"><a href="#species_Diorite">diorite</a> </td><td class="l"><a href="#species_OlivineGabbro">olivine-gabbro</a> </td><td class="l"><a href="#species_Gabbro">gabbro</a> </td><td class="l"><a href="#species_Peridotite">peridotite</a> </td><td class="l"><a href="#species_Pyroxenite">pyroxenite</a></td></tr>
-<tr><td class="l">Fragmental </td><td class="l"><a href="#species_Rhyolite">rhyolite</a>, <a href="#species_Tuff">tuff</a> or <a href="#species_Breccia">breccia</a> </td><td class="l"><a href="#species_Trachite">trachite</a>, <a href="#species_Tuff">tuff</a> or <a href="#species_Breccia">breccia</a> </td><td class="l"><a href="#species_Dacite">Dacite</a>, <a href="#species_Tuff">tuff</a> or <a href="#species_Breccia">breccia</a> </td><td class="l">andesite <a href="#species_Tuff">tuff</a> or <a href="#species_Breccia">breccia</a> </td><td colspan="4" class="l">Basalt <a href="#species_Tuff">tuffs</a> and <a href="#species_Breccia">breccias</a></td></tr>
-</table>
-<div class="pb" id="Page_178">178</div>
-<p>When it is located as igneous, turn to the key
-on <a href="#Page_177">page 177</a> and decide as to which type of texture
-is present. If glassy, the color, luster and
-type of construction will place it. If the rock is
-crystalline, first decide whether feldspar is present,
-and if present, what type: then determine
-the dark mineral, and lastly whether quartz or
-olivine is present. In dense rocks the presence
-of quartz may be determined by trying the hardness,
-for none of the other constituents of igneous
-rocks have so great hardness. For example, if it
-is found that a rock is composed of orthoclase
-hornblende and quartz, and the texture is granitoid,
-it is granite: or if the rock is plagioclase feldspar
-and pyroxene of any sort, it is gabbro, etc.</p>
-<h3><a id="species_Granite">Granite</a>
-<br /><a href="#Plate_53">Pl. 53</a></h3>
-<p>The combination of orthoclase
-feldspar (or microcline), quartz, and
-either mica, hornblende or augite is
-termed granite, if the texture is coarse enough so
-the individual minerals can be recognized with
-the unaided eye. The rock is light-colored because
-the feldspar and quartz dominate. Accessory
-minerals may be present such as apatite,
-zircon, beryl or magnetite. Varieties of granite
-are distinguished according to the dark mineral
-present. When this is muscovite, it is a <i>muscovite-granite</i>;
-when it is biotite, a <i>biotite-granite</i>; if
-it is hornblende, a <i>hornblende-granite</i>; etc. The
-size of crystals in granite varies widely. When
-they are as small as &sup1;/&#8321;&#8322; of an inch in diameter, it
-is termed fine grained; from &sup1;/&#8321;&#8322; to &frac14; of an inch,
-it is medium-grained; when larger, it is coarse-grained.
-In some cases the crystals may be over
-a foot in diameter which is known as <i>giant
-granite</i>.</p>
-<div class="pb" id="Page_179">179</div>
-<p>Originally granite was a great mass of molten
-magma, which has cooled very slowly, having
-been intruded or thrust up in great stocks or
-batholiths beneath overlying rocks, which acted
-as a blanket to prevent rapid cooling. These
-overlying rocks, in their turn, have been acted
-upon by the heat and metamorphosed. Granite
-is particularly likely to have been formed under
-mountain folds; so that, after the mountains
-have been more or less completely eroded away,
-the great masses of granite have come to the surface
-to mark the axes of the ranges; and even
-after the mountains have been wholly worn away,
-the granite remains to mark the sites on which
-they stood.</p>
-<p>In the granite mass itself, there are often veins
-and dikes, which probably resulted from the
-shrinkage of the cooling granite, and they are
-filled with a different and usually coarser granite
-known as <b>pegmatite</b>. This pegmatite formed
-from the residual magmatic material, so that as
-some of the elements had already crystallized
-out, the granite in these dikes is of different composition.
-The extreme coarseness of these pegmatites
-seems to be due to the character of the
-mineralizing agents left in the dikes. In some of
-these pegmatites the feldspar and quartz are so
-intergrown, that when broken along the cleavage
-surface of the feldspar, the quartz appears
-like cuneiform characters, and this variety has
-been given the name <i>graphic granite</i> (See <a href="#Plate_53">Plate 53</a>).</p>
-<p>When granite is exposed to weathering, the
-feldspar is the first mineral to be decomposed,
-<span class="pb" id="Page_180">180</span>
-altering eventually into carbonates, quartz and
-kaolin. The dark minerals are only slightly less
-susceptible and they break down into carbonates,
-iron oxides and kaolin. The original quartz
-remains unchanged. Of these products the carbonates,
-some of the iron oxide and a little of the
-quartz are carried away in solution. The kaolin
-and some of the iron oxide is in fine particles and
-they are carried by the water until it comes to
-the lakes or the sea. The quartz is left in coarser
-grains, which are more slowly transported, and
-deposited in coarser or finer sand and gravel beds.</p>
-<p>Granites are widely used for building stone,
-because they can be worked readily in all directions,
-and have great strength and beauty. The
-color depends largely on the color of the feldspar,
-which may be white or pink, in which case the
-granite will be gray to pink.</p>
-<p>Granites occur throughout New England, the
-Piedmont Plateau, the Lake Superior Region,
-the Black Hills, Rocky Mountains, Sierra Nevada,
-etc.</p>
-<h3><a id="species_Syenite">Syenite</a>
-<br /><a href="#Plate_54">Pl. 54</a></h3>
-<p>The combination of orthoclase
-and either mica, hornblende, or
-augite is syenite, the texture being
-coarse enough so that the individual minerals can
-be distinguished by the unaided eye. It differs
-from granite in the absence of quartz. Syenite
-is a light-colored rock with the feldspar predominating.
-Minerals like apatite, zircon, or magnetite
-may occur in it, as accessory minerals.
-The foregoing would be an ideal syenite, but
-usually there is some plagioclase feldspar also
-<span class="pb" id="Page_181">181</span>
-present. If this occurs in such quantities as to
-nearly equal the orthoclase feldspar, the rock is
-termed a <i>monzonite</i>; if it predominates, the rock
-becomes a diorite. The presence of quartz would
-make this rock into a granite. Such a compound
-rock has its type form, and when the proportions
-of the component minerals are changed, it grades
-into other types.</p>
-<p>Like the granite, syenite is an intrusive rock,
-which occurs in stocks and batholiths along the
-axes of present or past mountain ranges. The
-original magma welled up under the mountain
-folds, where it cooled slowly, metamorphosing the
-adjacent rocks. Like granite it has only been
-exposed after a long period of erosion has removed
-the overlying layers of rock.</p>
-<p>Syenites are not as abundant as granites, but
-they occur in the White Mountains, near Little
-Rock, Ark., in Custer Co., Colo., etc.</p>
-<h3><a id="species_QuartzDiorite">Quartz-Diorite</a></h3>
-<p>The combination of plagioclase
-feldspar, quartz and either mica or
-hornblende makes quartz-diorite,
-sometimes called <i>tonalite</i>. The above would
-be the typical quartz-diorite, but there is usually
-some orthoclase present, which if it equals
-the plagioclase feldspar in amount makes this
-into a monzonite; or if it dominates, it makes
-the rock a granite. Quartz-diorite is darker
-colored than the two preceding rocks, the dark
-minerals being about as abundant as the light-colored
-ones, such as feldspar and quartz. For
-this reason the weight is also somewhat greater.</p>
-<p>Like the others this is an intrusive rock, occurring
-<span class="pb" id="Page_182">182</span>
-in stocks and batholiths, and indicative
-of great molten masses thrust up under mountain
-folds, and only exposed after the overlying rocks
-have been weathered away. It is by no means an
-abundant type of rock, but occurs at Belchertown,
-Mass., Peekskill, N. Y., in the Yellowstone
-Park, etc.</p>
-<h3><a id="species_Diorite">Diorite</a></h3>
-<p>Plagioclase feldspar with hornblende
-or mica, or with both, is
-known as diorite. It is distinguished from
-quartz-diorite by the absence of quartz. There is
-generally some augite in it, but if this should be
-equal to, or exceed the hornblende, the rock is
-then a gabbro. There may also be a small
-amount of orthoclase present, without taking this
-rock out of the diorite class, but if the orthoclase
-feldspar becomes dominant, then the rock is a
-syenite. Thus there is gradation into other
-groups in all directions. Apatite, magnetite,
-zircon, and titanite often occur in small quantities
-as accessory minerals. Generally the hornblende
-is in excess of the feldspar, so that the
-rock is a dark-colored one.</p>
-<p>Diorites occur in much the same manner as
-granites, being in stocks, batholiths or dikes,
-and are often associated with granites and gabbros.
-They are great intruded masses, associated
-with mountain making, and like the preceding
-rocks, cooled far below the surface, and have
-been exposed only after great thicknesses of
-overlying rocks have been weathered away.</p>
-<p>Peekskill, N. Y., the Sudbury nickel district
-in Canada, Mt. Davidson above the Comstock
-<span class="pb" id="Page_183">183</span>
-Lode in Nevada, etc., are typical localities for
-finding diorite.</p>
-<h3><a id="species_OlivineGabbro">Olivine-Gabbro</a></h3>
-<p>The combination of plagioclase
-feldspar with augite (or any of the
-pyroxenes) and olivine makes olivine-gabbro.
-The feldspar is usually one of those
-with considerable calcium in it, like labradorite;
-and as the dark minerals predominate, the rock
-is dark-colored. It is an intrusive rock, usually
-in dikes or stocks, where it solidified far below
-the surface, and was only exposed after the overlying
-rocks were weathered off. It is by no
-means an abundant type of rock, but is found in
-the Lake Superior Region, and near Birch Lake,
-Minn.</p>
-<h3><a id="species_Gabbro">Gabbro</a>
-<br /><a href="#Plate_54">Pl. 54</a></h3>
-<p>Plagioclase feldspar with any one
-of the pyroxenes, most commonly
-augite, is gabbro. There is a wide
-range in the relative proportions of the two minerals
-making gabbro. At one extreme are rocks
-made entirely, or almost entirely, of plagioclase
-feldspar, which are known as <b>anorthosites</b>, and
-occur in parts of the higher mountains of the
-Adirondacks like Mt. Marcy, in several places in
-eastern Canada, etc. Then there are the typical
-gabbros where the feldspar and augite are more or
-less equally represented. At the other extreme
-come those gabbros in which the pyroxene predominates,
-in the most marked cases the feldspar
-being entirely lacking, and the rock being termed
-a pyroxenite. When the pyroxene of a gabbro is
-either enstatite or hyposthene (usually the latter)
-<span class="pb" id="Page_184">184</span>
-the gabbro is often called <b>norite</b>. Magnetite,
-biotite, and hornblende may occur in small
-quantities as accessory minerals.</p>
-<p>Gabbro is a common intrusive rock, occurring
-in stocks, batholiths, and dikes, and often varies
-considerably in different parts of the mass. Like
-granite the mass solidified far below the surface,
-under some mountain fold, and has only been
-exposed as the result of weathering away the
-layers of overlying rock. Gabbros appear much
-like diorites, but are distinguished by the fact
-that the dark mineral is one of the pyroxenes,
-instead of an amphibole or a mica. They are
-widely distributed, being found in the White
-Mountains, near Peekskill, N. Y., Baltimore,
-Md., about Lake Superior, in Wyoming, the
-Rocky Mts., etc.</p>
-<h3><a id="species_Peridotite">Peridotite</a></h3>
-<p>A rock made up of olivine and
-augite (or any of the pyroxenes) is
-peridotite. As it contains no feldspar, and both
-augite and olivine are dark-green to black in
-color, these rocks are always dark green to black
-in color and of considerable weight. They are
-usually rather coarsely crystalline. Peridotite is
-usually associated with gabbro, making dikes
-which lead from the main gabbro mass. Less
-frequently it occurs independently, making up
-an intrusive mass. Hornblende and mica may be
-present in small quantities, as accessory minerals.</p>
-<p>In general these are rather rare rocks, making
-dikes connected with stocks or batholiths of
-gabbro. Peridotite is found near Baltimore, Md.,
-in Custer Co., Colo., in Kentucky, etc.</p>
-<div class="pb" id="Page_185">185</div>
-<h3><a id="species_Pyroxenite">Pyroxenite</a></h3>
-<p>This represents the extreme among
-coarsely crystalline igneous rocks, a
-whole mass made up of one mineral, and that
-some one of the pyroxene group. If the mineral
-can be exactly determined, the rock may be still
-more definitely named. For instance if it is all
-augite, then the rock would be called augitite.
-Like the preceding rocks, pyroxenite is an intrusive
-rock, usually found in dikes, which are
-connected with gabbro, and it represents the segregation
-of one mineral out of the gabbro, and
-its solidification at one point. Hornblende,
-magnetite and pyrrhotite may be present as
-accessory minerals. This is not a common
-rock, but it illustrates the fact that all possible
-combinations do occur, if the circumstances
-have warranted it. It is found
-near Baltimore, Md., Webster, N. C., and in
-Montana.</p>
-<h3><a id="species_Rhyolite">Rhyolite</a></h3>
-<p>This is a combination of orthoclase
-feldspar, quartz, and either hornblende,
-mica or augite in which the crystals are
-of such small size that they can not be identified
-with the naked eye. In composition it corresponds
-to granite, but it is much finer in texture.
-It differs from trachite by having quartz while
-the latter has none. This can usually be determined
-by trying the hardness as none of the other
-minerals are as hard as 7. It is much harder to
-distinguish it from dacite which differs only in
-having plagioclase feldspar in place of the orthoclase,
-and only the microscope will enable one to
-make this distinction. Where the distinction
-<span class="pb" id="Page_186">186</span>
-cannot be made these light-colored lavas are
-often called <b>felsite</b>.</p>
-<p>Rhyolite is usually an extrusive lava, occurring
-in sheets, but sometimes it is intrusive, occurring
-in sills, dikes, and laccoliths. In all these cases
-the lava has solidified so rapidly, that the crystals
-are tiny, and only the general effect of a
-crystalline structure is distinguishable. Rhyolites
-may occur with porphyritic structure, in
-which case the presence of the larger feldspar
-crystals will help to distinguish whether they
-are orthoclase or not, making the determination
-easier. The color of rhyolites is green, red or
-gray, always a decided light shade.</p>
-<p>Rhyolites are abundant in the western states,
-as in the Black Hills, the Yellowstone Park,
-Colorado, Nevada, California, etc.</p>
-<h3><a id="species_Trachite">Trachite</a></h3>
-<p>The combination of orthoclase
-feldspar with mica, hornblende or
-augite is termed trachite, if the texture is dense.
-It is usually an extrusive lava of light color
-(green, red or gray), and corresponds in composition
-to syenite. It can be distinguished from
-rhyolite by having no quartz, and so nothing to
-show a hardness above 5.5; but it is difficult to
-distinguish it from andesite, which differs only
-in having plagioclase feldspar in place of orthoclase.
-It sometimes occurs with a porphyritic
-structure, in which case the feldspar crystals are
-usually large enough to be distinguished.</p>
-<p>Trachites are not abundant in America, but
-some are found in the Black Hills of South Dakota,
-in Custer Co., Colo., and in Montana.</p>
-<div class="pb" id="Page_187">187</div>
-<h3><a id="species_Dacite">Dacite</a></h3>
-<p>The union of plagioclase feldspar,
-quartz, and either hornblende or
-mica is termed dacite, if the texture is dense.
-It is an extrusive lava, occurring mostly in sheets
-and dikes. It corresponds in composition to
-quartz-diorite. As the texture is dense it is
-difficult to distinguish dacite from rhyolite, for
-both have quartz and differ only in the character
-of the feldspar, so it is quite common to use the
-term felsite which does not distinguish between
-the two, and only states that the rock is dense,
-light-colored and extrusive. When, as often
-occurs, the texture is porphyritic, and the feldspars
-are the large crystals, then exact determination
-is fairly easy.</p>
-<p>Dacites are rather common, occurring on McClelland
-Peak, Nev., in the Eureka district,
-Nev., on Lassen&rsquo;s Peak, Calif., Sepulchre Mt. in
-the Yellowstone Park, etc.</p>
-<h3><a id="species_Andesite">Andesite</a></h3>
-<p>The union of plagioclase feldspar
-with mica, hornblende or augite,
-makes andesite if the texture is dense. The lack
-of quartz, and so no mineral which has a hardness
-of over 5.5, makes it possible to distinguish
-andesite from dacite or rhyolite, but it is hard to
-distinguish this rock from trachite, which differs
-only on having orthoclase feldspar in place of
-plagioclase. When the texture is porphyritic and
-the feldspars are the large crystals, then it is easy
-to make the distinction. Andesite gets its name
-from being the characteristic lava of the Andes
-Mountains, and is the commonest of all the extruded,
-light-colored lavas, being the lava of
-<span class="pb" id="Page_188">188</span>
-hundreds of flows throughout the western United
-States.</p>
-<p>The union of plagioclase feldspar and biotite
-is the commonest type. Plagioclase with hornblende
-or augite is less common, and, when they
-do occur, they are usually distinguished as
-<i>hornblende-andesite</i> or <i>augite-andesite</i>. Magnetite,
-apatite and zircon may be present as accessory
-minerals.</p>
-<p>The lavas of Mt. Hood, Shasta, Rainier and
-others of the volcanic peaks of the Cascade
-Range, those at Eureka and Comstock in Nevada,
-in the Yellowstone National Park, and
-the porphyries of many peaks in Colorado, like
-the Henry Mts., etc., which are exposed laccolithic
-intrusions, are all andesites, as are many
-more.</p>
-<h3><a id="species_Basalt">Basalt</a></h3>
-<p>The combination of plagioclase
-feldspar with olivine and augite (or
-any other pyroxene) makes a heavy, dark-colored,
-black to dark-brown rock which, if its
-texture is dense or porphyritic, is termed basalt.
-This usually has more or less magnetite in it as an
-accessory mineral, indeed the magnetite may be
-so abundant as to be a component part of the
-rock. This magnetite makes trouble for anyone
-trying to use a compass on or about basalt rocks.
-These are extrusive or intrusive rocks and correspond
-in composition to gabbro.</p>
-<p>Basalts are among the commonest of igneous
-rocks, and are popularly designated &ldquo;<i>trap</i>,&rdquo; much
-used as a road ballast on account of its toughness,
-which is largely due to its dense texture. The
-<span class="pb" id="Page_189">189</span>
-coast of New England is seamed with dikes of
-basalt, and through the Adirondack and White
-Mountains there are a host of these dikes. The
-crests of such mountains, as the Holyoke Range,
-the Tom Range, the Talcott Mts., East and West
-Rocks at New Haven, etc., are all basalt sheets.
-The Palisades, First Wachung and Second Wachung
-Mountains of New Jersey are sills of
-basalt. The Lake Superior region is crisscrossed
-with basalt dikes. That greatest of all lava fields
-the Columbia Plateau, covering over 200,000
-square miles on the Snake and Columbia Rivers
-in Oregon, Washington and Idaho, is all basalt.
-So it goes all down through Nevada, New Mexico
-and California.</p>
-<h3><a id="species_Porphyry">Porphyry</a>
-<br /><a href="#Plate_55">Pl. 55</a></h3>
-<p>This is a term which properly refers
-to texture alone, indicating a
-lava, which has cooled in such a
-manner that one mineral has crystallized out of
-the magma first and developed to a larger size,
-while the mass of the material formed tiny crystals
-in which the larger ones are embedded. The
-large crystals are technically known as <i>phenocrysts</i>.
-The surrounding mass of tiny crystals
-is termed the <i>matrix</i>. This porphyritic structure
-is especially characteristic of lavas which
-have been extruded in large masses, and of
-intruded lavas in such places as sills and
-laccoliths.</p>
-<p>The term porphyry today has the above precise
-meaning. It is a much abused word, and
-has had all sorts of meanings. In the past it was
-first used to refer to lavas in general, then it came
-<span class="pb" id="Page_190">190</span>
-to be applied to lavas which had been erupted
-before Tertiary times, that is to all ancient lava
-sheets. This idea soon proved incorrect, lavas
-being of the same composition whether ancient
-or recent. In the West the word is often colloquially
-used today to designate almost every
-kind of igneous rock occurring in sheets or dikes,
-if in any way connected with ore deposits.</p>
-<p>When the composition of a rock with porphyritic
-textures can be determined, the name
-due to the composition is coupled with that due
-to texture, making such terms as <i>trachite-porphyry</i>,
-<i>basalt-porphyry</i>, etc.</p>
-<h3><a id="species_Tuff">Tuff</a></h3>
-<p>Tuff, a term not to be confused
-with tufa on <a href="#Page_215">page 215</a>, is the name
-used to designate the finer fragmental ejecta of
-volcanic eruptions, which are also often referred
-to as &ldquo;volcanic ash,&rdquo; but the word, ash, conveys
-the false impression that the rock is a remnant
-of something burned, and is therefore not a good
-term. When first ejected, tuff is loose material,
-but it is usually soon cemented to make a more
-or less firm mass of rock, for which the term, tuff,
-is still retained. In some cases, while still loose,
-it is carried by streams to a distance and deposited
-in more or less sorted and layered beds:
-and the finer tuff is often carried by the winds
-and laid down, at a considerable distance from
-its source, in so called &ldquo;ash beds.&rdquo; In both these
-cases, sedimentary characteristics have been
-added to the tuff, and layering which is characteristic
-of sedimentary deposits, is present.
-These transported tuff beds are really sedimentary,
-<span class="pb" id="Page_191">191</span>
-but as there is little change in the material,
-they are referred to here and not again. These
-tuff beds are not at all uncommon in the sedimentary
-deposits of Tertiary age in the Rocky
-Mountain region. The coarser material of
-volcanic eruptions usually goes under the head
-of breccia.</p>
-<h3><a id="species_Breccia">Breccia</a></h3>
-<p>This term is used to describe the
-coarse fragmental ejecta of volcanic
-eruptions. It is also used, in the section under
-sedimentary rocks, in a broad sense to include
-all angular unworn fragmental material, whether
-of igneous or sedimentary origin. For this
-reason, when dealing with igneous rocks, it is
-usual to designate the fragments according to
-their composition, making such terms as <i>trachite-breccia</i>,
-<i>rhyolite-breccia</i>, etc.</p>
-<p>While still loose (and also even when cemented
-into beds of rock), it is customary to designate
-the smaller fragments, from the size of a grain of
-wheat up to an inch or two in diameter, as
-<i>lapilli</i>; the larger fragments, from two inches
-up to a foot or so in diameter, as <i>bombs</i>; and the
-largest masses, often tons in weight, as <i>volcanic
-blocks</i>.</p>
-<h3><a id="species_Obsidian">Obsidian</a>
-<br /><a href="#Plate_55">Pl. 55</a></h3>
-<p>Lavas, which have cooled so
-quickly that crystals have not had
-time to form, have a glassy appearance,
-and are termed obsidian. If the color
-is dark, due to the presence of large amounts of
-those elements which make dark minerals, this
-lava is termed <i>basalt-obsidian</i>. Obsidian is
-<span class="pb" id="Page_192">192</span>
-characterized by its glassy texture, a hardness
-around 6, and by breaking with a conchoidal
-fracture, so called because the surface is marked
-by a series of concentric ridges, something like
-the lines of growth on a shell. Obsidians vary
-greatly in color, but are usually red or green to
-black, and translucent on thin edges. While
-glassy, all the obsidians contain embryonic
-crystals, which appear like dust particles floating
-in the glassy matrix, or there may even be a few
-larger crystals present, which are often arranged
-in flow lines. Most all large masses of obsidian
-have streaks or layers of stony material in them
-where crystallization has set in, in a limited
-way.</p>
-<p>Near the upper surface, obsidians usually have
-gas cavities scattered through them, and these
-may be small and few, or large and numerous.
-Indeed the cavities may be so numerous as to
-dominate and give the rock a frothy appearance.
-In this case, if the cavities are small and more or
-less uniform, the rock is called <i>pumice</i>; if they
-are larger it is <i>scoria</i>. If, as often happens
-when the lava is ancient and has been buried
-beneath other rocks, the cavities have been
-filled with some secondary mineral, then the
-lava is called an <i>amygdoloid</i>.</p>
-<p>Obsidian is found in many localities, especially
-where there are recent volcanoes, the most
-famous places being the obsidian cliffs in the
-Yellowstone Park, those near Mono Lake in
-California, and many other localities in the
-Rocky Mountains, the Sierra Nevadas, and the
-Cascade Mountains.</p>
-<div class="pb" id="Page_193">193</div>
-<h3><a id="species_Pitchstone">Pitchstone</a></h3>
-<p>This is very like obsidian in
-appearance, but differs in that the
-glassy material contains from five to ten per cent
-of water in its composition, the most obvious
-effect of which is to make the luster resinous,
-instead of vitreous, as is characteristic of obsidian.
-The colors are commonly red, green or
-brown. Pitchstone is associated with recent
-volcanoes, and some fine specimens have come
-from Silver Cliffs, Colo., and various parts of
-New Mexico and Nevada.</p>
-<h3><a id="species_Perlite">Perlite</a>
-<br /><i>pearlstone</i></h3>
-<p>Perlite is a glassy lava, containing
-two to four per cent of water, which,
-on cooling, has cracked into numerous
-rounded masses, with a concentric structure,
-reminding one of the layers of an onion.</p>
-<h3><a id="species_Scoria">Scoria</a></h3>
-<p>While lava is cooling, there is a
-constant escape of gases, mostly
-steam, and as these rise through the molten
-mass they make cavities, near the upper surface,
-that portion on top often becoming frothy. If
-this solidifies quickly so that the gas cavities are
-preserved it is scoria. When the gas cavities are
-small and uniformly distributed, the rock is
-called pumice, and often used as a scouring
-agent. When the cavities are large and irregular
-the term scoria is generally used. Molten lavas
-may form various structures, according to the
-conditions under which they cool, dripping
-through cracks or from the roof of caves, which
-often form where the molten lava escapes from a
-hardened shell, and making stalactites, stalagmites,
-<span class="pb" id="Page_194">194</span>
-etc. The very thin lava of the Hawaiian
-volcanoes may even be blown by the wind into
-fine threads, known as &ldquo;Pele&rsquo;s hair.&rdquo;</p>
-<p>The presence of the gas cavities is so characteristic
-of the upper surface of lavas which have
-been extruded; that, where one is dealing with
-older lavas, now buried beneath other rocks, this
-fact helps to determine whether the mass is a
-sheet, rather than a sill; for, in the case of the
-sill, the lava was forced between layers of
-sedimentary rocks, and the burden of the overlying
-rocks did not permit the escape of steam
-and therefore the upper surface of sills does not
-have the scoriaceous structure.</p>
-<h3><a id="species_Amygdoloid">Amygdoloid</a>
-<br /><a href="#Plate_56">Pl. 56</a></h3>
-<p>When the upper surface of a lava
-is filled with steam holes, and this
-lava has been buried beneath other
-rocks, the seeping waters slowly bring such
-minerals as quartz, calcite and zeolites and fill
-the cavities. Such a rock is known as an
-amygdoloid. It is often confused with porphyry;
-but, if examined closely, it will be seen
-that the outlines of the gas cavities are rounded,
-while the outlines of a crystal, like a phenocryst,
-are always angular. This will be clear if
-the amygdoloid on <a href="#Plate_56">Plate 56</a> is compared with
-the porphyry on <a href="#Plate_55">Plate 55</a>.</p>
-<h3 class="center"><span class="sc">The Sedimentary Rocks</span></h3>
-<p>To this class belong all those rocks which have
-been laid down by water or wind, or are the
-results of organic depositions. They include
-<span class="pb" id="Page_195">195</span>
-loose material like sand or day, and also the
-same materials, when cemented into more or
-less solid rocks, like sandstone or shale. So long
-as the material has not been altered from what
-it was when laid down, the rock is termed
-sedimentary.</p>
-<p>In general the material of which these rocks
-are composed comes from the weathering and
-disintegration of other rocks. This does not
-apply to the organic deposits, for each type of
-which there is a peculiar mode of formation.
-To illustrate the typical formation of sedimentary
-rocks, we may look at the fate of a granite
-when exposed. At once the surface is attacked
-by changes of temperature, frost and rain. The
-various minerals of the granite expand and contract
-with every change of temperature, but each
-component mineral has a different coefficient of
-expansion under heat, so that minute cracks are
-quickly formed between the minerals. Water
-gets into these cracks and begins to dissolve the
-minerals. Feldspar is the most easily attacked,
-part of it being dissolved and carried away, a
-small part changing to quartz, and by far the
-largest part changing to kaolin. The dark
-mineral is also attacked and partly dissolved,
-and partly changed to kaolin and iron oxides.
-The quartz resists solution almost completely.
-Of these products the kaolin and iron oxides
-are carried far away and deposited in still water.
-The quartz and perhaps some of the dark mineral
-are heavier and carried more slowly, being
-deposited as sand. This happens to granite
-everywhere, but in the regions where there is
-<span class="pb" id="Page_196">196</span>
-frost the action is greatly hastened; for water gets
-into the cracks and expands every time it freezes
-and thus widens the cracks rapidly, which greatly
-facilitates the entrance and movement of water
-in the rock. In a similar way any original rock
-will be disintegrated, and the residue, after the
-soluble part has been carried away, becomes sand
-or clay or mud.</p>
-<p>Particles of quartz, kaolin, and lime, separately,
-or mixed, loose or more or less cemented,
-with accompanying impurities, make up the
-great bulk of the sedimentary rocks. They
-are usually arranged in layers, of varying thickness,
-as they were laid down by water or the
-wind. In the same way layered accumulations
-which are either products of plants or animals,
-or parts of the plants or animals, are considered
-sedimentary, as for instance, coal, chalk, petroleum,
-etc.</p>
-<h3 class="center"><span class="sc">A Classification of Sedimentary Rocks</span></h3>
-<table class="center" summary="">
-<tr><td colspan="2" class="l">Inorganic origin:</td></tr>
-<tr><td class="r">1. </td><td class="l">Coarse fragmentary material resulting from weathering </td><td class="l">talus</td></tr>
-<tr><td class="r">2. </td><td class="l">The same fragmentary material cemented </td><td class="l">breccia</td></tr>
-<tr><td class="r">3. </td><td class="l">Unsorted material resulting from rock weathering </td><td class="l">soil</td></tr>
-<tr><td class="r">4. </td><td class="l">Coarse fragments rounded by the action of water and wind </td><td class="l">gravel</td></tr>
-<tr><td class="r">5. </td><td class="l">The same material cemented </td><td class="l">conglomerate</td></tr>
-<tr><td class="r">6. </td><td class="l">Finer material deposited by water or wind </td><td class="l">sand</td></tr>
-<tr><td class="r">7. </td><td class="l">The same material cemented </td><td class="l">sandstone</td></tr>
-<tr><td class="r">8. </td><td class="l">The finest material, mostly kaolin, deposited by water </td><td class="l">clay</td></tr>
-<tr><td class="r">9. </td><td class="l">The finest material, deposited by wind </td><td class="l">loess</td></tr>
-<tr><td class="r">10. </td><td class="l">The same material cemented </td><td class="l">shale</td></tr>
-<tr><td class="r">11. </td><td class="l">Fine particles of lime, pure or impure </td><td class="l">marl</td></tr>
-<tr><td class="r">12. </td><td class="l">The same material cemented </td><td class="l">limestone</td></tr>
-<tr><td class="r">13. </td><td class="l">Unassorted material left by the glacial ice </td><td class="l">till</td></tr>
-<tr><td class="r">14. </td><td class="l">The same material cemented </td><td class="l">tillite</td></tr>
-<tr><td colspan="2" class="l">Organic Origin:</td></tr>
-<tr><td class="r">15. </td><td class="l">Limes made from shells, etc. </td><td class="l">coquina, chalk, coral rock, etc.</td></tr>
-<tr><td class="r">16. </td><td class="l">Silica from the shells of plants, etc. </td><td class="l">diatomaceous earth, etc.</td></tr>
-<tr><td class="r">17. </td><td class="l">Carbon from plants </td><td class="l">peat, lignite, coal, etc.</td></tr>
-<tr><td class="r">18. </td><td class="l">Hydrocarbons from animals </td><td class="l">petroleum, asphalt, amber, etc.</td></tr>
-<tr><td class="r">19. </td><td class="l">Phosphates from animals </td><td class="l">guano, phosphate rock, etc.</td></tr>
-</table>
-<div class="pb" id="Page_197">197</div>
-<h3><a id="species_Talus">Talus</a></h3>
-<p>Where weathering is very active,
-especially on or below steep mountain
-slopes, a mass of loose, angular fragments
-accumulates. This material is termed talus, a
-term which refers only to the physical character
-of the material, and not at all to its composition.
-If weathering continues these fragments will be
-<span class="pb" id="Page_198">198</span>
-further broken up into one of the finer grained
-rocks, which the water can carry away and deposit
-elsewhere. There is little or no layering in
-talus. If the talus is not carried away but is
-cemented where it was formed, the resulting
-mass is termed breccia, but this is not very
-commonly the case.</p>
-<h3><a id="species_Breccia_rock">Breccia</a>
-<br /><a href="#Plate_58">Pl. 58</a></h3>
-<p>The term breccia is used to cover
-all those rocks which are composed
-of angular fragments, of any composition,
-and above sand in size, when they are
-cemented into a solid mass, by any sort of
-cementing agent. Here the term is used in its
-broad sense, as compared with the way it was
-used under igneous rocks.</p>
-<p>Breccias may result from the cementing of
-talus, but more often the breaking up of the
-material into angular fragments was due to
-other causes, such as crushing along a fault
-plane, or in the movements involved in mountain
-making. In such cases the breccia is of limited
-extent, but may occur repeatedly in the same
-neighborhood. Limestone, which has been
-crushed and then recemented, often makes a
-rock which takes a good polish and is used in
-several localities as an ornamental stone in place
-of marble, in fact often goes in trade circles
-under the name of &ldquo;marble.&rdquo; The breccia
-figured on <a href="#Plate_58">Plate 58</a> is such a limestone.</p>
-<h3><a id="species_Soil">Soil</a></h3>
-<p>Over most of the earth&rsquo;s surface
-there is a covering of rock waste,
-the product of weathering, some of which is
-<span class="pb" id="Page_199">199</span>
-unassorted, and some of it sorted by water or
-wind. This is all termed soil. It is an ever-moving
-cover resulting from the decomposition
-of the underlying rocks, to which have been
-added in places layers of rock waste brought
-from afar by the streams. Some soils are rock
-waste which had been carried clear to the ocean
-and deposited on the floor of the sea, and is now
-above sea level, because the floor of the sea
-has been elevated. Inasmuch as the underlying
-rocks vary in composition, and as there are
-areas of transported material, it is clear that
-the composition of soils must vary from place to
-place, both as to composition and texture.</p>
-<p>Soils range from the finest, composed mostly
-of clay, to coarse ones, composed of sand, gravel
-or even boulders. Clay, the finest grained soil,
-is composed of particles only about &sup1;/&#8321;&#8320;&#8320;&#8320;th of a
-millimeter in diameter, of which it would take
-720,000 billion particles to make a gram&rsquo;s weight.
-Ordinary soils however have about 2 to 5 million
-particles to the gram.</p>
-<p>The average specific gravity of soil with the
-usual amount of humus in it is from 2.55 to 2.75.
-In this case however the specific gravity is of
-less importance than is the volume weight. A
-cubic foot of water weighs 62&frac12; pounds, that of
-soil from 75 to 80 pounds, the extremes being
-30 lb. for peaty soil and 110 lb. for calcareous
-sand. The terms &ldquo;heavy&rdquo; and &ldquo;light,&rdquo; used
-in agriculture do not refer to the volume weight,
-for clay which is actually relatively light (70-75
-lb. per cubic foot) is classed as a &ldquo;heavy&rdquo; soil;
-while sand, of much greater actual weight, is
-<span class="pb" id="Page_200">200</span>
-classed as a &ldquo;light&rdquo; soil. These terms as used
-in agriculture refer to the ease with which the
-soils are worked, and to their penetrability by
-plant roots.</p>
-<p>Soil is usually divided into an upper darker-colored
-layer, termed loam, and into a lower,
-lighter-colored layer, termed subsoil. The presence
-of humus, resulting from the decomposition
-of plant and animal remains is the factor which
-darkens the color and distinguishes the loam; so
-that loam is a complex of inorganic rock particles
-plus more or less humus, colloid compounds,
-bacteria, living plants and animals. The subsoil
-is mainly rock particles. The distinctions
-between these two layers break down in arid
-soils, and often also in swampy regions.</p>
-<p>It is this layer of soil on which the water of
-every rain and flood works, picking part of it up
-and carrying it along, step by step, to the sea.
-Though the amount moved on any one day is
-small, the sum of all the soil transported is
-enormous, a large river carrying annual incredible
-amounts. For instance the Mississippi
-annually deposits in the Gulf of Mexico 476,900,000
-metric tons (2204 lb. to the metric ton), of
-which about a third is in solution. At this rate
-it takes about 7000 to 9000 years to remove a foot
-from over the whole drainage basin. This is
-considerably slower than is the case of some
-other rivers. While on the one hand soil is
-being continuously carried away from the surface,
-on the other hand it is being constantly
-renewed from below, by the weathering action of
-water, air and temperature.</p>
-<div class="pb" id="Page_201">201</div>
-<h3><a id="species_Gravel">Gravel</a></h3>
-<p>Gravel is a mass of loose fragments
-of rock, which have been
-rounded by water and deposited with little or no
-sorting, so that larger and smaller pebbles and
-sand all occur together. It is the deposit laid
-down by comparatively fast water in inland lakes
-or along the storm-beaten shores of the sea.
-Where a swift stream enters quiet water, as
-where it empties into a lake, there it quickly
-drops its coarse material as gravel, usually thus
-building a delta. Gravel also occurs in stream
-beds, where for any reason the rate of flow is
-checked. During the recent glacial period, the
-ice sheet brought down great masses of unsorted
-material, which was deposited as till, or in
-moraines. Much of this was then picked up by
-the running water and moved longer or shorter
-distances, so that, all over the glaciated country
-of the northern and eastern United States, there
-are unusually large numbers of gravel deposits.
-Gravels are all water laid, and usually show more
-or less clearly the bedded or stratified structure.</p>
-<p>The size of the component pebbles of gravel
-ranges from great boulders to fine sand, and the
-finer gravels grade into the coarser sands, the line
-between gravel and sand being drawn at about
-the size of a pea, the coarser being gravel, the
-finer sand.</p>
-<p>Gravel is widely used as ballast for railroads
-and in making highways, because of its tendence
-to pack well, while the hard pebbles resist wear.
-It is also widely used in concrete work, bonding
-in well with the cement, and making it go from
-three to five times as far.</p>
-<div class="pb" id="Page_202">202</div>
-<h3><a id="species_Conglomerate">Conglomerate</a>
-<br /><a href="#Plate_58">Pl. 58</a></h3>
-<p>Conglomerates are composed of
-rounded pebbles and sand of varying
-sizes, cemented together into a
-solid rock. The pebbles may run up to boulders
-in size, but they have all been more or less
-rounded by water, and transported some distance.
-The pebbles may all be of the same
-composition, or may represent a variety of rocks.
-When the pebbles are all, or most all, of one sort,
-the resulting conglomerate is termed a <i>quartz-conglomerate</i>,
-a <i>limestone-conglomerate</i>, a <i>gneiss-conglomerate</i>,
-etc. So too the cementing material
-varies in kind, silica, calcite and iron oxide being
-the commonest. The color will depend on both
-the component pebbles and the cement, sometimes
-one dominating, sometimes the other.
-There are some of the quartz- and limestone-conglomerates
-which can be cut and polished to
-make very handsome stone.</p>
-<p>Conglomerates represent consolidated gravels,
-and always indicate an aqueous origin, quite
-often the delta of an ancient stream, or the
-invasion of the sea over the land; so they have
-become of importance to geologists in interpreting
-past events.</p>
-<h3><a id="species_Sand">Sand</a></h3>
-<p>Sand is a mass of small rock particles,
-from the size of a pea down to
-&sup1;/&#8325;&#8320;&#8320; of an inch in diameter. The material may
-be any sort of rock, or a mixture of two or more
-kinds. Sand may be the result of the disintegration
-of older rocks at the point where it
-is now found, in which case the grains have the
-shapes they had in the original rock; but more
-<span class="pb" id="Page_203">203</span>
-often the sand grains have been transported
-greater or lesser distances, and in the process
-have been more or less rounded.</p>
-<p>Those sands, which lie where they were formed
-are called <i>residual</i>, and such sand is usually composed
-of a mixture of angular grains, some harder
-and others softer, such as quartz, feldspar, mica
-and hornblende, all mixed together. Where the
-sand has been transported, only the more resistant
-minerals have remained, such as quartz,
-magnetite, cassiderite, etc.; with which there
-are at times rarer minerals, such as gold,
-platinum, garnets or topaz. Such sands are
-known as <i>gold-bearing</i>, <i>topaz-bearing</i>, etc.</p>
-<p>The sands from different localities differ
-greatly. The streams gather the rock particles,
-and sort them according to the size, which the
-water flowing at any given rate can carry.
-When the water is slowed down, it drops all the
-particles above the size which the new rate of
-speed can handle. The grains of sand from the
-bed of a stream are usually more or less angular.
-The further they are carried, the more they are
-knocked together and rounded; so that after
-being carried to the sea, and then thrown up on
-the beaches, they have been well rounded,
-especially the larger grains. As the air is less
-viscid than the water, sand which is transported
-by the wind, is even more rounded; so that desert
-sands show the most complete rounding, indeed
-are even polished; and this is true even of the
-smaller grains. It is the wind-blown, or desert
-sands, which flow so evenly in an hourglass. Between
-the angular residual sands and the
-<span class="pb" id="Page_204">204</span>
-polished desert sands, there are of course all
-grades. Glacial sands are angular or &ldquo;sharp&rdquo;
-almost to the degree characteristic of residual
-sands; and lake-shore sands are between river
-sands and sea sands in the degree of rounding.</p>
-<p>Sands made of particles of lime, <i>calcareous
-sands</i>, are less resistant to wear than are those
-of quartz. In regions where the water is &ldquo;soft&rdquo;
-(free from lime), they do not last long, as they
-are dissolved; but in a limestone region where
-the water is &ldquo;hard&rdquo; (saturated with lime), the
-grains are not so quickly dissolved and may
-accumulate into beds of great thickness, as in
-Florida. Along some shores of the ocean, there
-occur &ldquo;green sands,&rdquo; which are ordinary quartz
-sands mixed with the dark green mineral glauconite,
-which is a potassium iron silicate, forming
-on the ocean bottom as a result of the action of
-decaying animal matter on iron-bearing clays
-and potassium-bearing silicates, like feldspar.
-This is particularly characteristic of some of the
-sands along the coast of New Jersey.</p>
-<p>In places, especially in the beds of rivers, there
-occur &ldquo;quicksands.&rdquo; This is a deposit of fine
-sand, mixed with a considerable amount of clay,
-and saturated with water; so that it will not
-support the weight of a man or an animal.
-Much that goes under the name of quicksand is
-a fluid mud, covered with a thin layer of sand.</p>
-<p>Sand is used for a wide variety of commercial
-purposes, and under these conditions gets various
-trade names; for instance &ldquo;glass sand&rdquo; is a pure,
-colorless to white, quartz sand, which is used as
-one of the components in making glass. It must
-<span class="pb" id="Page_205">205</span>
-be free from impurities, as these color the glass,
-and much of the sand used for this purpose is
-quartz, crushed to a fine sand-like condition.
-&ldquo;Moulding sand&rdquo; is a rather fine-grained quartz
-sand, with a small but very definite admixture of
-clay, and this is used to make the moulds for
-castings in foundries. &ldquo;Polishing sand&rdquo; is one
-composed of angular fragments of quartz, usually
-from stream beds or glacial deposits, or even
-crushed quartz, and is used for cutting and
-polishing marble, for sandpaper, and for polishing
-wood and softer stones. There are many
-other special uses, like building, ballast, filters,
-furnaces, etc., in which quartz sand is used, being
-screened if necessary to get the right sizes.</p>
-<h3><a id="species_Sandstone">Sandstone</a></h3>
-<p>When sand of any sort is cemented
-so as to make a solid rock, it is
-termed sandstone, which varies widely according
-to the size, color and composition of the
-grains, and also with the sort and amount of
-the cement. When the size of the grains is
-larger than that of a pea, sandstone grades into
-conglomerate; when smaller than &sup1;/&#8325;&#8320;&#8320;th of an
-inch, especially if mixed with clay, it grades into
-shale. There are all grades of firmness, due to
-the amount and kind of cement, ranging from
-those which have little or no cement, but are
-compact as a result of the pressure of the overlying
-rocks, to those in which the cement has
-filled all the pore spaces. In general there is
-a considerable amount of space between the
-grains of sand; so that a sandstone will absorb
-large amounts of water, up to 25% of its bulk.
-<span class="pb" id="Page_206">206</span>
-In moist climates where it freezes, this makes
-many sandstones unsuitable for use as building
-stones, as they are likely to spale, or chip off, as
-is seen in the &ldquo;brown stone&rdquo; so much used in
-New York City.</p>
-<p>Sandstones are usually bedded rocks and are
-relatively easy to quarry, and most of them are
-not so firmly cemented, but that they can be
-readily worked or cut into shape by the stone
-cutter; and so, certain sandstones are very
-popular for building stone or for trimming on
-buildings, where they are not too much exposed
-to the weather.</p>
-<p>Sandstone gets a variety of names according
-to the cement.</p>
-<p><b>Siliceous sandstone</b> is cemented with silica
-and usually very hard.</p>
-<p><b>Calcareous sandstone</b> is cemented with lime
-and usually rather soft.</p>
-<p><b>Ferruginous sandstone</b> is cemented with one
-of the iron oxides.</p>
-<p><b>Argillaceous sandstone</b> is held together with
-clay impurities, and is usually both soft and of
-undesirable color.</p>
-<p>According to their composition there is also a
-number of varieties.</p>
-<p><b>Arkose</b> is a sandstone composed of quartz and
-feldspar grains, usually derived from the disintegration
-of granite and not transported far.</p>
-<p><b>Graywacke</b> is a sandstone composed of quartz,
-feldspar, and some other mineral, like hornblende-augite,
-etc., also derived from the disintegration
-of granites and not transported far.</p>
-<p><b>Grit</b> is a term applied to a coarse sandstone,
-<span class="pb" id="Page_207">207</span>
-composed of angular quartz fragments, and used
-to a considerable extent for millstones.</p>
-<p><b>Flagstone</b> is a thin bedded sandstone, often
-with mica, which splits easily and uniformly
-along the bedding planes; so that it can be quarried
-in large slabs. It was widely used for sidewalks
-before the advent of concrete.</p>
-<p><b>Freestone</b> is a thick-bedded sandstone, not
-over hard, so called, because it can be worked
-freely and equally well in all directions.</p>
-<h3><a id="species_Clay">Clay</a></h3>
-<p>Clay is a term used to describe a
-mass of fine particles, the most
-prominent property of which is plasticity when
-wet. Clays range from masses of pure kaolin
-to masses of kaolin and related minerals mixed
-with as much as 60% of impurities, which may
-be sand, lime, iron oxides, etc. The particles of a
-fine clay range around &sup1;/&#8321;&#8320;&#8320;&#8320; of a millimeter in diameter,
-while the impurities may be, and usually
-are, of larger size, up to the size of sand grains.</p>
-<p>All clays are of secondary origin, the result of
-weathering, especially of feldspars, though clays
-may also result from the weathering of serpentines,
-gabbros, etc. In some cases after the
-weathering of feldspar or limestones, the clay
-may remain just where it was formed, as a
-residual deposit; but, being so fine-grained, it is
-usually transported by rain water or by the wind
-and deposited somewhere else as a sedimentary
-bed. The quiet waters of a lake are favorable
-places for such deposits, and many clay beds
-represent former lake bottoms. Impure clays
-are often laid down on the flood plains of sluggish
-<span class="pb" id="Page_208">208</span>
-streams. In fresh water the settling of the
-clay is a very slow process, requiring days, or
-when very fine, weeks, before the water wholly
-clears. In salt water, however, the clay sort of
-coagulates, the particles gathering together in
-tiny balls, which settle rapidly, so that the water
-is soon clear.</p>
-<p>According to their mode of origin clays are
-classified as residual, sedimentary, marine,
-swamp, lake, flood-plain, eolian, etc. But when
-their uses are considered a very different classification
-is made, based mostly on their composition,
-and we speak of China clays or kaolins, fire
-or refractory clays, paving-brick clays, sewer-pipe,
-stone-ware, brick, gumbo and slip clays.</p>
-<p>The <b>kaolin</b> or <b>china clays</b> are residual clays,
-usually resulting from the decomposition of
-pegmatite dikes. They must be white when
-burned, free from iron oxides, and fairly plastic.
-A good deal of china clay is made by crushing
-feldspar.</p>
-<p><b>Ball clays</b> are sedimentary clays which remain
-white when burned, are usually very plastic, and
-free from iron oxides. They are mostly used in
-the making of various sorts of china.</p>
-<p><b>Fire clays</b> may or may not have iron oxides in
-them, but they must be free or nearly free from
-fluxing materials, such as lime, magnesia and the
-alkalies (sodium and potassium compounds).
-They may be more or less plastic, the essential
-quality being their ability to withstand high temperatures
-without fusing. Silica (as sand) tends
-to diminish the refractory quality; so that a clay
-otherwise suitable, if it has sand in it, becomes at
-<span class="pb" id="Page_209">209</span>
-best a second grade fire clay. In coal mining
-sections it is customary to term those beds of clay
-either above or below the coal, &ldquo;fire clay&rdquo;; but
-this is an unfortunate designation, for though
-some of them are true fire clays, the most of them
-are not.</p>
-<p><b>Stone-ware clays</b> are those with considerable
-sand and up to five per cent of fluxing materials.
-They must be plastic enough to be readily
-worked, and then burn to a dense body at comparatively
-low temperatures.</p>
-<p><b>Sewer-pipe clays</b> must be plastic, and carry
-a considerable amount of fluxing material, as the
-surface of the pipe is expected to vitrify in the
-burning.</p>
-<p><b>Brick clays</b> are low grade clays and vary greatly
-in composition. The main requisites are that
-they mould easily and bake hard at relatively
-low temperatures with as little warping and
-cracking as possible. As most clays shrink both
-in the air drying and in the baking, sand is added
-when the clay is being mixed. The color is
-mostly due to the presence of iron impurities.
-If there are iron oxides and little or no lime, the
-brick bakes to a red color, but if there is an excess
-of lime over the iron oxides, it bakes to a cream
-or buff color, which on vitrifying turns green.</p>
-<p><b>Paving-brick clays</b> range from surface clays,
-to semirefractory clays, shale being often used.
-The essential component is enough fluxing material,
-so that the bricks shall begin to vitrify, or
-fuse, at not too high temperatures.</p>
-<p><b>Slip clays</b> are those with a high percentage of
-fluxing material; so that, when baked at moderate
-<span class="pb" id="Page_210">210</span>
-temperatures, the surface fuses into a glassy
-brown or green glaze.</p>
-<p><b>Adobe</b> is an impure calcareous clay, widely
-used in the western United States for making
-sun-dried bricks.</p>
-<p><b>Gumbo</b> is a term applied to fine-grained plastic
-clays which shrink too much in the burning to
-be useful in manufactures. They can be burned
-to make an excellent ballast for railroads and
-highways. They are especially abundant in the
-Middle Western States.</p>
-<h3><a id="species_Loess">Loess</a></h3>
-<p>This is the name given to a fine
-grained homogeneous clay-like material,
-which is a mixture of clay, fine angular
-fragments of sand, flakes of mica and more or
-less calcareous matter. It is usually without
-stratification, and cleaves vertically, so that,
-when eroded, it forms steep cliffs. Loess covers
-great areas in the Mississippi Valley, in the Rhine
-Valley, and in North Central China. By some
-it is thought to be an accumulation of dust in
-those regions where the prevailing winds were of
-diminished velocity and where the grass or other
-vegetation has served to catch and hold the
-material; by others it is thought of as a river
-and lake deposit; and by still others it is thought
-to be due to the combination of the two modes,
-wind and flood. The writer inclines to the first
-view expressed.</p>
-<h3><a id="species_Shale">Shale</a>
-<br /><a href="#Plate_59">Pl. 59</a></h3>
-<p>When pure or impure clays, or
-loess, are consolidated, they are all
-grouped under the name shale. It
-usually possesses a layered or stratified structure,
-<span class="pb" id="Page_211">211</span>
-which makes it possible to split it into thin
-layers. Of all the sedimentary rocks shale is the
-commonest, and it may occur in all the places
-where clay could occur, but the most widely
-distributed shale is that which made the sea
-bottom of former times and is more or less calcareous,
-like the piece on <a href="#Plate_59">Plate 59</a>, in which bits
-of shells are still visible. Shale has the same
-wide variation in composition as has clay, the
-various types being designated according to the
-impurity which is present, as:</p>
-<p><i>argillaceous shale</i>, made mostly of clay,</p>
-<p><i>arenaceous shale</i>, shale with more or less sand
-as an impurity,</p>
-<p><i>calcareous shale</i>, or one with more or less lime
-as an impurity,</p>
-<p><i>ferruginous shale</i>, or one with iron compounds
-as impurities,</p>
-<p><i>bituminous shale</i>, or one colored black by the
-presence of organic matter, remains of either
-plants or animals.</p>
-<p>While of no value as building material, shale
-may be ground or crushed, and used as a substitute
-for any corresponding clay, and thus many
-manufacturers use shale in making fire-clay
-products, bricks, tile, etc.</p>
-<h3><a id="species_Marl">Marl</a></h3>
-<p>Where limestones or shells of any
-sort have been pulverized, and
-mixed with more or less impurities, especially
-clay, the resulting unconsolidated mass is known
-as marl. It is usually associated with marine
-formations, and is the finer d&eacute;bris which has
-settled on the ocean bottom well out from shore,
-<span class="pb" id="Page_212">212</span>
-that is out beyond the sandy and mud deposits.
-Finding it therefore usually indicates a sea
-bottom recently elevated. It is very characteristic
-of the southern coastal states, from
-Maryland all along to Texas.</p>
-<h3><a id="species_Limestone">Limestone</a></h3>
-<p>Any mass of marl, or aggregate of
-calcareous shells, corals, etc., which
-has become consolidated is known as limestone.
-It may, and usually does, have a wide range of
-impurities, chief of which are clay, sand, iron
-oxides, and bituminous matter, like plant or
-animal remains. Pure limestone is white, but
-due to impurities it ranges through grays, greens,
-browns, to black, and even red, but this last is
-rarer. It is easily identified by the presence of
-calcium carbonate, which effervesces in hydrochloric
-acid. It most often represents deposits
-in fairly deep water on ocean bottoms of the past,
-but there is also a wide range of limestones
-which were formed in fresh water.</p>
-<p>Limestone is often burned at temperatures
-just above 900&deg; C, at which point carbon dioxide
-goes off as a gas, and leaves calcium oxide, or
-lime. When this is mixed with water it makes
-calcium hydroxide, or slaked lime, which is
-mixed with sand to give it body, and is used as
-mortar. When exposed to the air, the slaked
-lime gives up water, and takes back from the air
-carbon dioxide, and again becomes calcium
-carbonate with its original hardness. Limestone
-is also used as one of the elements in all cements.
-It is also considerably used as a building stone,
-which, however, suffers in moist climates from
-<span class="pb" id="Page_213">213</span>
-the solution of its lime by rains, but has stood up
-very well in dry climates.</p>
-<p>The varieties of limestone are mostly distinguished
-according to their mode of origin,
-some of them being as follows.</p>
-<p><b>Bog Lime</b> is a white calcareous powdery deposit
-on the bottom of ponds in limestone regions,
-a deposit precipitated from solution by the
-action of the plants inhabiting the ponds.</p>
-<p><b>Coquina</b> (<a href="#Plate_59">Plate 59</a>) is the rock formed by the
-rather loose consolidation of shells and shell fragments.
-It is particularly characteristic of tropical
-regions, and is very abundant near St.
-Augustine, Fla., in which region it was, and still
-is, cut into blocks and used for building stone.
-In that mild climate it has stood very well.</p>
-<p><b>Chalk</b> (<a href="#Plate_60">Plate 60</a>) is a soft fine-grained limestone,
-formed in the ocean by the accumulation
-of myriads of the tiny shells of Foramenifera,
-which are single celled animals, living either a
-floating life near the surface of the sea, or a
-creeping life on the bottom. Chalk is composed
-mostly of the shells of floating Foramenifera,
-which when the animals died, settled to the
-bottom and there accumulated, mostly at depths
-of 600 feet or more. When the mass of unconsolidated
-shells is dredged up from depths of
-50 to 2000 fathoms, it is known as <i>Foramenifera
-ooze</i>. Chalk beds are then indications of an
-uplifted sea bottom. When consolidated, if
-pure or nearly so, it makes a white chalk, and the
-beds may be of considerable thickness, as is the
-case of the famous cliffs near Dover on either
-side of the English Channel. One of Huxley&rsquo;s
-<span class="pb" id="Page_214">214</span>
-most famous lectures is the one on chalk, found
-in his <i>Essays and Lay Sermons</i>.</p>
-<p><b>Coral Rock</b> is made by the cementation of fragments
-of corals. The binding material, as in most
-stones, is lime; and this sort of rock is associated
-with coral reefs of either the past or the present.
-One of the best illustrations of this being the
-&ldquo;Dolomite Mountains&rdquo; in Tyrol. Coral rock,
-like coquina, has been cut into blocks and used as
-building stone, as in Bermuda.</p>
-<p><b>Encrinal Limestone</b> (<a href="#Plate_60">Plate 60</a>) is a rock made
-by the cementation of fragments of the skeleton
-of crinoids. These animals belong to the group,
-echinoderms, and are now extinct except for a
-few so called &ldquo;sea-lilies.&rdquo; They were animals
-with a central mouth surrounded by long, jointed,
-flexible arms in multiples of five, and below this a
-small body inclosed in calcareous plates, all at
-the top of a long jointed stem. They lived in
-the sea and in the earlier geological times must
-have been very abundant; for their remains are
-so common in places as to make whole layers of
-limestone.</p>
-<p><b>Hydraulic Limestone</b> is a fine-grained, compact,
-yellowish limestone with from 13 to 17%
-of sand, and some clay; which, when it is burned
-at a temperature a little higher than that used in
-burning lime, makes a product, that, while not
-as strong as Portland cement, still like it sets
-under water.</p>
-<p><b>Lithographic Limestone</b> is a very fine-grained,
-compact limestone with clay impurities, the
-finest of the grain making it usable for making
-the stone plates used in lithographic printing.
-<span class="pb" id="Page_215">215</span>
-On slabs of this limestone figures are drawn in
-reverse with a special crayon. Then the slab is
-treated with acid, those parts which are not protected
-by the drawing being etched away, while
-the points protected by the drawing remain in low
-relief. From this slab figures can then be printed.</p>
-<p><b>Travertine</b> is a general name, applied to calcareous
-deposits from fresh water lakes or
-streams, and has been precipitated either as a
-result of cooling or evaporation. Some travertines
-are porous, while others are dense; some are
-white, while others are colored, often beautifully,
-by impurities in the water.</p>
-<p>Porous deposits of travertine, when made on
-grass or other like substances, are known as tufa
-or <i>calc sinter</i>. Such masses are common around
-Caledonia, N. Y., Mammoth Hot Springs in the
-Yellowstone Park, etc.</p>
-<p><b>Onyx marble</b> is a dense travertine, usually
-formed as a result of the deposition of lime from
-the water of springs. It is often banded, due
-to the presence of impurities in the water at one
-time, and their absence at other times.</p>
-<h3><a id="species_Till">Till</a></h3>
-<p>Till is an unconsolidated mass of
-boulders, pebbles, sand and fine clay,
-the unsorted material left behind by glaciers
-when they melted. The boulders and pebbles,
-while they show some wear, are not rounded like
-those that have been transported by streams,
-but have a more or less angular shape; and some
-of them are polished or striated on one side,
-where, while frozen in the ice, they were rubbed
-along the bottom.</p>
-<div class="pb" id="Page_216">216</div>
-<p>One of the most recent geological events in
-America was the extension of the ice sheet, now
-covering Greenland, down over north and northeastern
-North America, until it extended as far
-south as northern New Jersey, the Ohio River
-and the Missouri River, and as far west as the
-Rocky Mountains, but not over the Great Basin,
-the Cascade Ranges or Alaska. This great
-mass of ice, thousands of feet thick, moved from
-two centers, one either side of Hudson Bay,
-scraping up the loose soil, and grinding off the
-exposed surfaces of the underlying rock. All
-this material it carried southward, until the
-melting along its lower margin equaled the rate
-at which it advanced. When the melting was
-faster than the advance the glacial sheet retreated.
-At the southern limit of the advance
-this d&eacute;bris was dropped, either making long ridges
-(moraines) or while the ice was retreating, thicker
-or thinner sheets. This deposited d&eacute;bris is till.</p>
-<p>The soil, and especially the subsoil, in all the
-regions formerly covered by the ice sheet, is made
-up very largely of this till; which, where it is
-undisturbed is often called &ldquo;hardpan.&rdquo; When
-till is mixed with humus it becomes loam. This
-mixture of material, varying all the way from the
-fine powdered products of the ice grinding
-to the great boulder it picked up and carried
-south, is characteristic of this or any other
-glaciated country. When this section of country
-was settled, the boulders and stone were a hindrance
-to cultivation, and were picked up and
-piled into stone walls, which are one of the first
-features to strike the eye.</p>
-<div class="pb" id="Page_217">217</div>
-<h3><a id="species_Tillite">Tillite</a></h3>
-<p>When till is consolidated into solid
-rock, it is known as tillite. In
-several cases it has been found buried far beneath
-the more recent sedimentary rocks; testifying
-that there were other glacial periods beside the
-last one which furnished the till.</p>
-<h3 class="center"><span class="sc">The Coal Series</span></h3>
-<p>Disregarding minor constituents, the plants
-are largely made up of cellulose, which is a
-combination of carbon, hydrogen, and oxygen,
-(C&#8326;H&#8321;&#8320;O&#8325;). If this is heated in the air, where
-there is plenty of oxygen, it disintegrates, or
-burns, making carbon dioxide and water; but if
-the heating is done where the oxygen is excluded,
-as in a kiln, the hydrogen and oxygen
-will be driven off and the carbon will remain
-behind as charcoal. In Nature similar reactions
-go on, but more slowly. Vegetable matter,
-exposed to the air, disintegrates into carbon
-dioxide and water, and there is no solid residue.
-However, if the vegetable matter is under
-water, which excludes the air more or less
-completely including the oxygen in it, then
-disintegration still takes place, but the products
-formed are water, (H&#8322;O) marsh gas (CH&#8324;), and
-some carbon dioxide (CO&#8322;), but a considerable
-part of the carbon remains behind and
-accumulates.</p>
-<p>Thus in bogs, swamps and ponds, where dead
-vegetation, especially that growing in the water,
-piles up, the oxidation is incomplete; so that
-there gradually accumulates on the bottom a
-<span class="pb" id="Page_218">218</span>
-layer of brown to black mud, known as <i>peat</i>.
-More plant remains are constantly being added,
-and the layer may increase to several feet in
-thickness. The decomposition is incomplete
-and some oxygen and hydrogen remain, but the
-carbon is in a constantly increasing ratio and
-in proportion far above that in cellulose. In
-the cold northern climates sphagnum moss is
-the most efficient peat producing plant, but in
-temperate and tropical climates the moss is
-replaced by the leaves, twigs, trunks, etc., of
-trees, bushes, and vines.</p>
-<p>If these peat beds are buried beneath a layer or
-layers of sediment, especially clay, the peat is
-sealed up and oxidation stops almost entirely.
-With the pressure of the superincumbent beds,
-the peat becomes more and more compact, and
-changes to a dark-brown or black color. It is
-then known as <i>lignite</i>. If this lignite is buried
-still deeper, with consequently more pressure
-and more time, it changes into the still denser
-black <i>bituminous coal</i>. This is as far as it will
-go unless some new agent is added to the forces
-already working.</p>
-<p>The next step in the series of changes forming
-coal is associated with mountain making. In
-case the layers of rock containing beds of coal are
-folded, and that presupposes at least a moderate
-increase in heat, the bituminous coal is altered
-to <i>anthracite</i>, which is still denser, and so hard
-that it breaks with a conchoidal fracture.
-Alteration may be carried a step still farther,
-in case the rocks between which lie beds of coal
-are effected by such high temperatures as accompany
-<span class="pb" id="Page_219">219</span>
-metamorphism. Then all the associated
-hydrogen, oxygen and moisture are driven
-off, and only the carbon remains, which is
-then known as <i>graphite</i>. All steps between
-the stages especially designated occur. The
-following represent steps only in the series of
-changes.</p>
-<h3><a id="species_Peat">Peat</a></h3>
-<p>Peat is a mass of unconsolidated
-vegetable matter, which has
-accumulated under water, and in which the
-original plant remains are still, at least in part,
-discernible. It contains a large amount of
-water, so that before it can be used as a fuel, it is
-cut out in blocks, which are piled up and left
-for a time to dry before using. It burns with a
-long flame and considerable smoke. This country
-is so well supplied with other fuels, that so
-far peat has been but little used.</p>
-<h3><a id="species_Lignite">Lignite</a>
-<br /><i>brown coal</i></h3>
-<p>Lignite is more compact than
-peat, and is found buried to some
-depth under layers of clay or sandstone.
-It is dark brown to black in color, and
-still retains pretty clear traces of the plants
-from which it was derived. It also usually contains
-a considerable amount of moisture, and
-when this is dried out, it tends to crumble badly,
-so that it is undesirable to handle it much, or to
-ship it far, before using. It has a fair fuel value
-and is fairly widely used; but it is very desirable
-that some method be found, by which lignite
-could be treated to obtain its by-products, and at
-the same time make it more compact, so it would
-<span class="pb" id="Page_220">220</span>
-not crumble with the handling incident to using
-it in furnaces. There are extensive lignite
-deposits in this country in North and South
-Dakota, Montana, Wyoming, Colorado, New
-Mexico, Texas, Louisiana, and Mississippi.</p>
-<h3><a id="species_BituminousCoal">Bituminous Coal</a>
-<br /><i>soft coal</i></h3>
-<p>This type of coal is compact, black
-in color, and breaks readily, but does
-not crumble as badly as lignite. It
-contains considerable water, and still has some
-hydrogen and oxygen compounds in it. Bituminous
-coal is the product of plant remains
-which have been preserved for long periods,
-(millions of years), sealed from the air by the
-overlying beds of rock. The pressure has made
-it compact, and nearly all traces of the original
-plants have disappeared.</p>
-<p>Bituminous coal is our most abundant fuel,
-occurring the world over in seams from less
-than an inch in thickness to some over fifteen
-feet thick. The United States is peculiarly
-fortunate in the abundant and easily accessible
-deposits of this type of coal, in Pennsylvania,
-West Virginia, Ohio, Kentucky, Tennessee,
-Indiana, Illinois, Michigan, Iowa, Missouri,
-Kansas, Nebraska, Texas, Utah, and Colorado.</p>
-<p>The volatile constituents, hydrogen and oxygen
-compounds, of bituminous coal may be
-driven off by heating the coal in closed ovens,
-and the residual mass is known as <i>coke</i>, almost
-pure carbon. This is distillation, and the ovens
-in which this is done, without trying to save the
-volatile products, are called bee-hive ovens,
-while the more modern ovens which save the
-<span class="pb" id="Page_221">221</span>
-by-products are called by-products ovens. A
-ton of bituminous coal treated in the typical
-by-products oven, will yield on the average 1410
-lb. of coke, 7.1 gallons of tar, 18.9 pounds of
-ammonia sulphate, etc., 2.4 gallons of light oils,
-10440 cubic feet of illuminating gas, about half
-of this last being used to furnish the heat for
-the distillation. The coal-tar dye industry is
-built on the tar thus produced. Toluol, benzol,
-etc., come from the light oils; and half the gas
-produced is available for household illumination,
-etc. Coke is demanded, as it is a superior fuel
-for melting iron ores, iron and steel, and is made
-regardless of whether the by-products are used.
-The coke thus produced is hard, clean, and
-vesicular; but for some reason as yet unknown,
-by no means all bituminous coal will produce a
-coke which has this porous structure. These
-latter are known as &ldquo;non-coking,&rdquo; and are of
-little use to the steel industry.</p>
-<h3><a id="species_CannelCoal">Cannel Coal</a></h3>
-<p>This is a compact variety of non-coking
-bituminous coal, with a dull
-luster and a conchoidal fracture. It
-contains the largest proportion of volatile hydrocarbon
-compounds of any variety of coal; so that
-when the supply of petroleum and natural gas
-gives out, this will be one of the important
-sources of obtaining substitutes. Cannel coals
-occur in Ohio, Indiana, and eastern Kentucky.
-This cannel coal owes its peculiar fatty nature
-to the material from which it is derived, it being
-supposed to have resulted from the accumulation
-of the spores of lycopod trees, and their conversion
-<span class="pb" id="Page_222">222</span>
-to jelly-like masses by bacteria in the
-fresh-water marshes of those ancient days.</p>
-<h3><a id="species_Anthracite">Anthracite</a>
-<br /><i>hard coal</i></h3>
-<p>Anthracite coal is hard, black,
-has a luster, and breaks with a
-conchoidal fracture. It contains but
-a low percentage of volatile matter, and so burns
-with a short flame, and less smoke, than is the
-case with the other coals. It is always associated
-with folded rocks, and appears to have
-been formed as a result of the combined pressure
-and the higher temperatures, which accompanied
-mountain making. Still the temperature was
-not high enough to metamorphose the adjacent
-rocks. Most of our anthracite comes from
-northeastern Pennsylvania.</p>
-<h3><a id="species_Carbonite">Carbonite</a></h3>
-<p>Carbonite is natural coke. It
-occurs in coal seams which have been
-cut by dikes or intrusions of igneous rocks, the
-coal having been thus coked by natural processes.
-It is not vesicular like artificial coke, for which
-reason it is not useful as a fuel. Some carbonite
-is found in the Cerillos coal field of New Mexico,
-in Colorado, and Virginia.</p>
-<h3><a id="species_Jet">Jet</a></h3>
-<p>Jet is a dense variety of lignite, a
-fossil wood of black color, which
-takes a high polish and cuts easily into various
-ornamental shapes. It has been used for
-ornaments since early ancient times, beads of jet
-being found in the early bronze period in England,
-the supply probably coming from the
-Yorkshire coast, whence the principal supply
-<span class="pb" id="Page_223">223</span>
-comes even to the present day. In Switzerland
-and Belgium it was used still earlier, even as far
-back as the Pal&aelig;olithic age. Jet seems then
-to have had a talismanic value, and to have been
-worn to protect the owner. About 700 <span class="small">A.D.</span> crosses
-and rosaries began to be made of jet, the custom
-starting at Whitby Abbey, the material being
-obtained nearby, so that it came to be known as
-&ldquo;Whitby jet,&rdquo; and in the eighteenth century became
-very popular. In recent times it has been
-used mostly as jewelry suitable for mourning.</p>
-<h3><a id="species_Amber">Amber</a>
-<br /><a href="#Plate_61">Pl. 61</a></h3>
-<p>Amber is a gum which oozed from
-coniferous trees and was petrified.
-It is associated with lignite beds of
-middle Tertiary age. It is usually pale-yellow
-in color, but at times has a reddish or brownish
-tinge, and is more or less transparent. It
-occurs in rounded irregular lumps, up to ten
-pounds in weight, though most pieces are
-smaller; and is mostly picked up along certain
-coasts where it is washed ashore by the waves.
-Since the earliest records amber has been cast
-up on the shores of the Baltic, and it was used by
-peoples as early as in the stone age for ornaments
-and amulets. It has been found among
-the remains of the cave dwellers of Switzerland,
-in Assyrian and Egyptian ruins of prehistoric
-age, and in Mycen&aelig; in the prehistoric graves of
-the Greeks, the first recorded reference to it being
-in Homer, and the Greek name for amber being
-<i>elektron</i> from which our word electricity comes.
-All these finds were of Baltic amber which was
-doubtless gathered and traded by those early
-<span class="pb" id="Page_224">224</span>
-men. Even down to the present many men
-make their living, riding along the shore at low
-tide and hunting for the amber washed ashore
-by the waves. As early as 1860 the German
-geologists concluded that the source of the
-amber must be lignite beds outcropping beneath
-the sea level, and started mining for the
-amber with fair success, so that today two types
-of Baltic amber are distinguished, &ldquo;sea stone&rdquo;
-which is washed ashore, and &ldquo;mine stone&rdquo;
-taken from the mines. Beside the Baltic locality,
-it is found along the shores of the Adriatic,
-Sicily, France, China, and occasionally of
-North America.</p>
-<p>Some pieces of amber are found with insects
-inclosed and preserved almost as perfectly as if
-collected yesterday. They were apparently
-entangled in the gum while still viscid and
-completely embedded, before fossilization.</p>
-<h3 class="center"><span class="sc">The Petroleum Series</span></h3>
-<p>Certain sedimentary rocks contain larger or
-smaller quantities of natural gas, petroleum,
-mineral tar and asphalt. These are compounds
-of carbon and hydrogen, or hydrocarbons, and
-range from gases to solids, each being a mixture
-of two or more hydrocarbon compounds. The
-crude petroleum may have either a paraffin base
-or an asphalt base: in the former case, when the
-gas, gasoline, kerosene, etc., have been removed
-by distillation, the solid residue will be paraffin,
-as in most of the Pennsylvania crude oils; while
-in the latter case, the solid residue will be an
-<span class="pb" id="Page_225">225</span>
-asphalt, as in most of the California and Texas
-crude oils. In the case of the paraffin series all
-the compounds belong to the paraffin group,
-while the asphalt is due to the presence, in addition
-to the paraffin group, of some of the benzine
-series of hydrocarbons.</p>
-<p>Petroleum is found in sands and shales, which
-were originally deposited on ancient sea bottoms,
-the shales generally being the real source of the
-petroleum. The oil was once the fatty portion
-of animal bodies (perhaps to some extent of plant
-bodies), and was separated during decomposition
-as a result of bacterial activity. Oil thus produced
-is in tiny droplets, which have a great
-affinity for clay. After being freed by the
-bacteria, the oil droplets in muddy water attach
-themselves to particles of clay, and as the clay
-settles the oil is carried down with it, the two
-eventually making a bituminous shale. In clear
-water, or in water which is in motion, the oil
-droplets rise to the surface and eventually distill
-into the air.</p>
-<p>The oil, or petroleum, may stay diffused
-through the shales, in which case we have <i>oil-bearing
-shales</i>, with sometimes as much as 20%
-of oil. Were there but &sup1;/&#8321;&#8320;&#8320;&#8320; of a per cent of oil
-in a layer of shale 1500 feet thick, this would
-amount to 750,000 barrels per square mile which
-is equal to a rich production from wells. When
-the oil in shale amounts to three per cent or more,
-it is commercially usable. There are large
-stretches of petroleum-bearing rocks in New
-York, Pennsylvania, Ohio, Indiana, and all the
-way out to the Pacific coast, some of them with
-<span class="pb" id="Page_226">226</span>
-oil so abundant, that a blow of the hammer will
-cause them to smell of petroleum.</p>
-<p>In case these oil-bearing shales have been
-heavily overburdened and compressed, the
-petroleum may have been more or less completely
-pressed out of them. Then the droplets
-uniting have formed a liquid, which has moved
-out from the shale, and gone wherever it could
-find open spaces. Sandstones have frequently
-offered their pore space, and as it filled, have
-been thus saturated with petroleum. If the
-sandstones were open to the air, or if fissures
-extended from them to the surface, the oil has
-escaped to the surface and evaporated into the
-air. But in those cases where the sandstone
-(or other permeable rocks) was covered by an
-impervious layer, like a dense shale or clay, the
-oil was confined below the covering layer of
-rock. Crude oil is lighter than water; so that
-when natural gas, petroleum and water were all
-present in the rocks, the gas lies on top, the
-petroleum next, and the water underneath.
-With this in mind it is easy to see, that in slightly
-folded or undulating layers of rock, the gas and
-petroleum would be caught under upraised folds
-and domes. This is the basis of prospecting for
-oil.</p>
-<p>If petroleum-bearing layers are depressed far
-enough beneath the surface to be affected by the
-high temperatures of the earth&rsquo;s interior, or have
-been near volcanic activity, of course the petroleum
-has been distilled by natural processes,
-and at most only the residues, like paraffin or
-asphalt, have remained. For this reason it is
-<span class="pb" id="Page_227">227</span>
-impossible to find petroleum in igneous or metamorphic
-rocks.</p>
-<h3><a id="species_NaturalGas">Natural gas</a></h3>
-<p>Natural gas is the lightest portion
-of crude oil, and consists mostly of
-marsh gas (&ldquo;fire damp,&rdquo; CH&#8324;) together with other
-light hydrocarbons, like ethane (C&#8322;H&#8326;), ethylene
-(C&#8322;H&#8324;), and some carbon dioxide and
-monoxide. It is colorless, odorless, and burns
-with a luminous flame. Mixed with air it is
-explosive. It is found in sedimentary rocks,
-mostly sandstones, either with or without petroleum.
-Usually it is under considerable pressure,
-and escapes with great force wherever
-a hole permits. In time the gas all escapes
-through the hole or well, and then the well
-&ldquo;runs out.&rdquo; If petroleum is present under
-the natural gas, the hole may become an &ldquo;oil
-well,&rdquo; from which petroleum may be pumped,
-until it in turn is exhausted. The end of an
-oil supply is usually indicated by the appearance
-of water in the well. Natural gas is mostly
-associated with oil districts, as in Pennsylvania,
-Ohio, Illinois, Texas, California, etc.</p>
-<h3><a id="species_PetroleumCrudeOil">Petroleum Crude Oil</a>
-<br /><a href="#Plate_61">Pl. 61</a></h3>
-<p>Petroleum is a mixture of paraffin
-compounds all the way from the
-gases, through gasoline, kerosene,
-lubricating oils, and vasoline to paraffin. In
-some of the crude oils there is also an admixture
-of compounds from the benzine series, in which
-case, when all the volatile compounds have been
-distilled off, an asphalt remains. The different
-components of petroleum may be separated out
-<span class="pb" id="Page_228">228</span>
-by heating the crude oil in closed tanks, and
-drawing off the various substances at the proper
-temperatures.</p>
-<p>Petroleum occurs in sedimentary rocks of marine
-origin, usually rocks which also contain the
-shells of some of the animals, the soft parts of
-which made the oil. To have been preserved
-the millions of years since the petroleum was
-first formed, the oil-bearing layers must have
-been covered by some impervious layer of rock,
-beneath the domes and anticlines of which the
-oil has lain ever since. When such a dome or
-anticlinal fold is perforated by a well, the
-released oil flows to the surface with a greater or
-less rush, according to the pressure. Wells may
-keep flowing for 20 years, sometimes more, sometimes
-much less. Those which flow with the
-greatest pressure usually are relatively short
-lived, at times lasting only a year or two. When
-this easily obtained oil is exhausted, there is an
-even greater supply to be obtained by the distillation
-of the bituminous shales. Petroleum
-never occurs in igneous or metamorphic rocks,
-but is found in either sandstones or shales, in
-places favorable for accumulation, all across that
-great stretch of ancient sea bottoms, extending
-from the Appalachian Mountains to the Rocky
-Mountains, and in the Great Basin between the
-Rocky Mountains and the Sierra Nevada Range,
-and also to the west of the Sierras.</p>
-<h3><a id="species_Bitumen">Bitumen</a></h3>
-<p>Where petroleum has escaped
-through pores in the rocks, or by way
-of fissures, and has come to the surface of the
-<span class="pb" id="Page_229">229</span>
-earth, the lighter components, thus exposed to
-the air, have vaporized and escaped, leaving
-behind a more or less solid residue, which is
-known as bitumen. If the escape was through a
-fissure, the bitumen may have accumulated in
-the fissure until it was filled, making vein bitumen.
-Or the escape may have been so rapid that
-the petroleum formed a pool or lake from the
-surface of which evaporation took place. In
-time such a pool will give off the gases and
-volatile compounds, only a residue remaining
-to make a pitch lake, like the one at Rancho Le
-Brea near Los Angeles, or an asphalt lake like
-the one on the island of Trinidad. On account
-of their varying hardness and composition, some
-of these bitumens have received special names; as:</p>
-<p><b>Albertite</b>, a black bitumen with a brilliant
-luster on broken surfaces, a hardness between 1
-and 2, and a specific gravity a shade over 1.</p>
-<p><b>Grahamite</b>, a black bitumen, which is brittle,
-but has a dull luster, a hardness of 2, and a specific
-gravity of 1.15.</p>
-<p><b>Gilsonite</b> or <b>Uintaite</b>, a black bitumen with a
-brilliant luster and a conchoidal fracture, a
-hardness of 2 to 2&frac12;, and a specific gravity of
-1.06.</p>
-<p><b>Malta</b> is a semi-liquid viscid natural bitumen,
-which has a considerable distribution in California.</p>
-<p>The above varieties of bitumen look a good
-deal like coal, but are easily distinguished by
-their lightness (weight about half that of coal),
-and the fact that with only moderate heat they
-melt, and become a thick liquid like tar.</p>
-<div class="pb" id="Page_230">230</div>
-<h3><a id="species_Guano">Guano</a></h3>
-<p>Guano is the accumulation of the
-excrement of birds (or of other animals
-like bats) on areas so dry that, though
-soluble, it is not leached and washed away. It
-may also contain some of the bones and mummified
-carcasses of the birds which died on the spot.
-The greatest of these deposits are on several small
-islands, just off the west coast of Peru, and now
-&ldquo;farmed&rdquo; by the Peruvian government. In this
-country there are no true guano beds, except a
-few accumulations of bat guano in certain caves
-of Kentucky and Texas, but these are not large
-enough to become of commercial importance.</p>
-<h3><a id="species_PhosphateRock">Phosphate Rock</a></h3>
-<p>Phosphate rock is one composed
-chiefly of calcium phosphate along
-with various impurities, such as clay
-and lime. It occurs in beds, irregular masses,
-or as concretionary nodules in limestone or sand.</p>
-<p>The bedded varieties are in the older sedimentary
-rocks, in which the phosphate runs
-from a small percentage up to as high as 85%.
-Ultimately the phosphate came from either
-animal excrement, or from bacterial decomposition
-of animal carcasses and bones. In all the
-beds it seems to be true that in the first instance
-the phosphate was laid down as a disseminated
-deposit in marine beds, usually limestones.
-Later by the action of water leaching through
-the rocks, the phosphate was dissolved, and then
-redeposited elsewhere in a more concentrated
-form. This may be either in the underlying
-sandstones, but is more often in limestones,
-replacing the original lime.</p>
-<div class="pb" id="Page_231">231</div>
-<p>In these secondary deposits, if the phosphate
-has been laid down in cavities, the resulting
-phosphate will be in nodular masses. In the case
-of the Florida and Carolina deposits, these
-nodules have been freed from their matrix and
-washed along the river beds, remaining as
-pebbles in the river sands. The bed deposits
-are mostly in Kentucky and Idaho. The commercial
-use for such phosphate rocks is of course
-the making of fertilizers.</p>
-<h3><a id="species_DiatomaceousEarth">Diatomaceous Earth</a>
-<br /><a href="#Plate_62">Pl. 62</a></h3>
-<p>Diatoms are tiny single-celled
-plants living in uncounted millions
-in the fresh and salt water. Each
-diatom builds around itself two shells which fit
-into each other like the cover and box of a pill-box,
-and each shell is marvelously ornamented.
-The shells are composed of silica of the opal
-type. In size the diatoms range from &sup1;/&#8325;&#8320;&#8320;&#8320; of an
-inch in diameter up to the size of a pin head, and
-they live in such numbers that ordinary surface
-waters have hundreds of them to the quart, and
-where they are flourishing up to 250,000 in a
-quart. When the plants die, or in order to
-reproduce abandon the shells, these shells fall
-to the bottom of the pond or the sea, and there
-accumulate, often making a layer from a few
-inches thick up to hundreds of feet in extreme
-cases. If unconsolidated, this mass of tiny
-shells is known as diatomaceous earth; but if
-they are consolidated it is called tripolite, so
-named because the first of them used commercially
-came from Tripoli.</p>
-<p>As the shells are tiny and uniform in size and
-<span class="pb" id="Page_232">232</span>
-have a hardness of 6, the diatomaceous earth is
-used to make a great variety of polishes, scouring
-soaps, tooth paste, as a filler in certain kinds of
-paper, in making waterglass, as an absorbent for
-nitroglycerine, and as packing in insulating compounds,
-where asbestos would otherwise be used.</p>
-<p>Deposits of freshwater diatoms are found all
-over the United States, usually in thin layers of
-limited extent, especially in Massachusetts, New
-York, Michigan, etc. The marine deposits of
-diatoms are on a much larger scale, there being
-beds of diatoms in Anne Arundel, Calvert and
-Charles Counties, Md., up to 25 or 30 feet in
-thickness. In Santa Barbara County, Cal.,
-there is one bed 2400 feet thick and another 4700
-feet thick, beside many other smaller ones. The
-enormous former wealth of life indicated by these
-great deposits may be suggested, when it is
-remembered that it takes about 120,000,000 to
-make an ounce in weight. They reproduce on an
-average about once in five days, so that from a
-single diatom the offspring possible under favorable
-conditions would amount to over 16,000,000
-in four months or over 60 tons in a year. Of
-such an order is the potential increase of animals
-or plants, no matter how small, if the rate of
-reproduction is high.</p>
-<h3 class="center"><span class="sc">Metamorphic Rocks</span></h3>
-<p>Either a sedimentary or an igneous rock,
-which has been altered by the combined activities
-of heat, pressure and chemical action,
-becomes a metamorphic rock. The process is
-<span class="pb" id="Page_233">233</span>
-essentially one, during which the layers of rock
-come under the influence of such temperatures
-as are associated with the formation of granite
-or lavas. Such material as is actually melted
-becomes igneous rock, but adjacent to the
-masses actually melted are other rocks which do
-not melt but, according to the temperature, are
-more or less changed, and these are the metamorphic
-rocks. At a distance from the molten masses
-the changes are minor, but close to the molten
-magmas extensive changes take place. Though
-not actually melted the rock near the heat center
-may be softened, usually is, in which case pebbles
-and grains or even crystals become soft and plastic,
-and, as a result of the great pressure, are
-flattened, giving the rock, when it cools again, a
-striated appearance. At these high temperatures
-the water in the rock and also some other
-substances vaporize, and the hot steam and
-vapor are active agents in making a great many
-chemical changes. In some cases material like
-clay is changed into micas, or chlorite, etc.; in
-other cases the elements of a mineral will be
-segregated and large crystals will appear
-scattered through the metamorphic rock, such as
-garnets, staurolites, etc.</p>
-<p>If one studies a layer of rock both near and far
-from the molten mass, all grades of change will
-appear. For example, at a distance a conglomerate
-maybe unaltered; somewhat nearer the
-molten mass, the heat and steam may have softened
-(but not melted) the pebbles and then the
-pressure has flattened them as though they were
-dough; and nearest the molten mass, the outlines
-<span class="pb" id="Page_234">234</span>
-of the pebbles are lost, only a layered effect
-remaining, and many of the materials have
-changed into new minerals, like mica, garnets,
-etc., but still the layered effect is preserved.</p>
-<p>One of the effects of heat and pressure is to
-flatten the component particles of the rock, so
-that it tends to split in a direction at right angles
-to the direction of the pressure, just as particles
-of flour are softened and flattened under the
-pressure of the roller; and then when the crust
-is baked it splits or cleaves at right angles to
-the direction in which the pressure was exerted
-by the roller. This tendency to split is not to be
-confused with either the layering, characteristic of
-sedimentary rocks, nor the cleavage characteristic
-of minerals. It has nothing to do with the
-way the particles were originally deposited, nor
-with their cleavage; but is due to the pressure,
-and resembles the pie crust splitting, being
-irregular and flaky. This is designated <i>schistosity</i>
-if irregular and <i>slaty cleavage</i> if regular.
-Schistosity refers to the flaky manner of splitting
-into thin scales as in mica schists. Slaty
-cleavage is more regular, this being due to the
-fact that the material of which slate is made is
-small particles of clay of uniform size.</p>
-<p>The metamorphic rocks are generally more or
-less folded, as they are always associated with
-mountain making. These major folds are of
-large size, from a hundred feet across to several
-miles from one side to the other. Such folds may
-also occur in sedimentary rocks or even in igneous
-rocks and simply express the great lines of yielding,
-or movement of the crust of the earth. In
-<span class="pb" id="Page_235">235</span>
-addition to this there is minor folding or contorting
-which is characteristic of metamorphic rocks
-only. When the rocks were heated by their
-nearness to the molten igneous magmas, they
-must expand, but being overburdened by thick
-layers of other rocks, there is no opportunity for
-yielding vertically, so the layers crumple, making
-minor folds from a fraction of an inch to a few
-feet across. Such crumpling, which is so very
-conspicuous especially where there are bands of
-quartzite in the rock, is entirely characteristic of
-metamorphic rocks. It is seen on hosts of the
-rocks about New York City, all over New England,
-and in any other metamorphic region.
-<a href="#Plate_63">Plate 63</a> is a photograph of such a crumpled rock
-which has been smoothed by the glacial ice.</p>
-<p>The metamorphic rocks are the most difficult
-of all the rocks to determine and understand,
-because the amount of change through which
-they have gone is greatest, but for this same
-reason they offer the most interest, for the
-agents which caused the changes are of the most
-dramatic type of any that occur in Nature.
-From one place to another a single layer of metamorphic
-rock changes according to the greater
-or less heat to which it was subjected, making
-a series of related rocks of the same composition
-but with varied amount of alteration. For this
-reason in naming metamorphic rocks, a type is
-named, and from that there will be gradations
-in one or more directions, both according to
-composition, and according to amount of heat
-involved. If it is possible to follow a given layer
-of metamorphic rock from one place to another
-<span class="pb" id="Page_236">236</span>
-this is of great interest; for by this means, many
-variations in the type will be found, both those
-resulting from a different amount of heat, and
-those due to the local changes in the composition
-of the original rock.</p>
-<p>One further consideration has to be kept in
-mind. When a rock is metamorphosed the
-high temperatures either drive off all water, or
-the water may be used up in the making of some
-of the complex minerals. When such a metamorphic
-rock later comes near the surface and is
-exposed to the presence of ground water, and
-that leaching down from the surface into the
-rocks, several of the minerals formed at high
-temperatures will take up this water and make
-new minerals such as serpentine, chlorite, etc.
-They are always associated with metamorphic
-rocks, and have been metamorphic rocks, but
-since then have become hydrated, forming minerals
-not at all characteristic of high temperature.</p>
-<p>The following shows the relation of the
-sedimentary and igneous rocks to their metamorphic
-equivalents.</p>
-<table class="center" summary="">
-<tr class="th"><th><i>Loose sediment</i> </th><th><i>Consolidated sediment</i> </th><th><i>Metamorphic equivalent</i></th></tr>
-<tr><td class="l"><a href="#species_Gravel">gravel</a> </td><td class="l"><a href="#species_Conglomerate">conglomerate</a> </td><td class="l"><a href="#species_Gneiss">gneiss</a></td></tr>
-<tr><td class="l"><a href="#species_Sand">sand</a> (<a href="#species_Quartz">quartz</a>) </td><td class="l"><a href="#species_Sandstone">sandstone</a> </td><td class="l"><a href="#species_Quartzite">quartzite</a></td></tr>
-<tr><td class="l">mud (<a href="#species_Sand">sand</a> and <a href="#species_Clay">clay</a>) </td><td class="l"><a href="#species_Shale">shale</a> </td><td class="l"><a href="#species_Schist">schist</a></td></tr>
-<tr><td class="l"><a href="#species_Clay">clay</a> </td><td class="l"><a href="#species_Shale">shale</a> </td><td class="l"><a href="#species_Slate">slate</a> or <a href="#species_Phyllite">phyllite</a></td></tr>
-<tr><td class="l"><a href="#species_Marl">marl</a> </td><td class="l"><a href="#species_Limestone">limestone</a> </td><td class="l"><a href="#species_Marble">marble</a></td></tr>
-<tr><td class="l"><a href="#species_Peat">peat</a> </td><td class="l"><a href="#species_BituminousCoal">bituminous coal</a> </td><td class="l"><a href="#species_Anthracite">anthracite</a> to <a href="#species_Graphite">graphite</a></td></tr>
-<tr><td class="l"> </td><td class="l">coarse igneous rocks such as <a href="#species_Granite">granite</a>, <a href="#species_Syenite">syenite</a>, etc. </td><td class="l"><a href="#species_Gneiss">gneiss</a></td></tr>
-<tr><td class="l"> </td><td class="l">fine igneous rocks such as <a href="#species_Trachite">trachite</a>, <a href="#species_Rhyolite">rhyolite</a>, etc. </td><td class="l"><a href="#species_Schist">schist</a></td></tr>
-</table>
-<div class="pb" id="Page_237">237</div>
-<p>In working out the past history of any given
-region, much of it is done on the basis of this
-series of equivalents. The finding of limestone,
-for instance, indicates that the given area was
-at one time under the sea to a considerable depth,
-that is from 100 to 1000 feet, but not ocean-bottom
-depths which run in tens of thousands of
-feet. Marble indicates the same thing, and so
-one can go on through all these types of rock.</p>
-<h3><a id="species_Gneiss">Gneiss</a>
-<br /><a href="#Plate_64">Pl. 64</a></h3>
-<p>Gneiss is an old word used by the
-Saxon miners, and is often very
-loosely used. Here it is used in its
-structural sense, and a gneiss may be defined
-as: a banded metamorphic rock, derived either
-from a sedimentary or an igneous rock, and is
-composed of feldspar, quartz, and mica or hornblende,
-and is coarse enough, so that the constituent
-minerals can be determined by the eye.
-It corresponds to a granite, or some sedimentary
-rock like gravel or conglomerate.</p>
-<p>Due to the action of pressure, all the gneisses
-are banded, and the original constituent particles
-or crystals are distorted. The lines of
-banding may be long or short, straight, curved or
-contorted. When the banding is not conspicuous,
-the gneiss tends toward a granite.
-When the banding is thin and the structure
-appears flaky, the gneiss tends toward a schist.
-The color varies according to the constituent
-minerals, from nearly white, through red, gray,
-brown, or green to nearly black. <a href="#Plate_64">Plate 64</a> shows
-one gneiss which is in a less advanced stage, the
-pebbles being simply flattened and the matrix
-<span class="pb" id="Page_238">238</span>
-partly altered to micaceous minerals, and a
-second gneiss which is so far advanced that the
-original constituents are all altered to other
-minerals and only the banded structure remains.
-This latter type would have required but little
-more heat to have completed the melting and
-changed this to a granite.</p>
-<p>Gneisses are very compact and have little or
-no pore space in them. They are hard and
-strong and resist weathering well, so that they
-are widely used as building stone: but they are
-not as good as granite for this purpose, as they
-split more readily in one direction and can not
-therefore be worked so uniformly as can
-granite.</p>
-<p>There are many varieties of gneiss, based
-either on their origin, composition, or their
-structure, as follows:</p>
-<dl class="undent"><dt><b>Granite-gneiss</b> is one derived by metamorphism from granite.</dt>
-<dt><b>Syenite-gneiss</b> is one derived by metamorphism from syenite.</dt>
-<dt><b>Diorite-gneiss</b> is one derived by metamorphism from diorite.</dt>
-<dt><b>Gabbro-gneiss</b> is one derived by metamorphism from gabbro.</dt>
-<dt><b>Biotite-gneiss</b> is one composed of quartz, feldspar and biotite.</dt>
-<dt><b>Muscovite-gneiss</b> is one composed of quartz, feldspar and muscovite.</dt>
-<dt><b>Hornblende-gneiss</b> is one composed of quartz, feldspar and hornblende.</dt>
-<dt><b>Banded-gneiss</b> is one in which the banded structure shows clearly.</dt>
-<dt><b>Foliated-gneiss</b> is one in which there is thin irregular layering.</dt>
-<dt><b>Augen-gneiss</b> is one which has concretionary lumps scattered through it.</dt></dl>
-<div class="pb" id="Page_239">239</div>
-<p>Gneisses have a wide distribution over all New
-England, most of Canada, the Piedmont Plateau,
-the Lake Superior region, the Rocky Mountains,
-the Sierra Nevada and the Cascade Ranges.</p>
-<h3><a id="species_Quartzite">Quartzite</a></h3>
-<p>Quartzite is metamorphosed sand
-or sandstone, and frequently grades
-into one or the other. It is a hard compact
-crystalline rock, which breaks with a splintery or
-conchoidal fracture. It is distinguished from
-sandstone by the almost complete lack of pore
-spaces, its greater hardness and by its crystalline
-structure. In practice it may be distinguished
-by the fact that a sandstone in breaking separates
-between the grains of sand, while a quartzite
-breaks through the grains.</p>
-<p>Some quartzites are almost pure quartz, but
-others contain impurities of clay, lime or iron,
-which were in the original sandstone. These
-alter in the metamorphism to such accessory
-minerals as feldspar, mica, cyanite, magnetite,
-hematite, calcite, graphite, etc. The color of
-quartzite when pure is white, but may be altered
-to red, yellow, or green by the presence of these
-accessory minerals.</p>
-<p>On account of the difficulty of working the
-quartzites, they are not much used in building,
-though they are very durable. When crushed
-they often make excellent road ballast, or filling
-for concrete work. The pure varieties are sometimes
-<span class="pb" id="Page_240">240</span>
-ground and used in the manufacture of glass.</p>
-<p>According to the accessory mineral, the following
-varieties may be distinguished; chloritic-quartzite,
-micaceous-quartzite, feldspathic-quartzite,
-etc.</p>
-<p>Quartzites are common in the New England,
-the Piedmont Plateau, and Lake Superior metamorphic
-regions, and also in many western
-localities.</p>
-<h3><a id="species_Schist">Schist</a>
-<br /><a href="#Plate_65">Pl. 65</a></h3>
-<p>Schist is a loosely used term, but
-is used here in its structural sense.
-It includes those metamorphic rocks
-which are foliated or composed of thin scaly
-layers, all more or less alike. The principle
-minerals are recognizable with the naked eye.
-In general schists lack feldspar, but there are
-some special cases in which it may be present.
-Quartz is an abundant component of schists; and
-with it there will be one or more minerals of the
-following groups: mica, chlorite, talc, amphibole
-or pyroxene. Frequently there are also accessory
-minerals present, like garnet, staurolite,
-tourmaline, pyrite, magnetite, etc.</p>
-<p>All schists have the schistose structure, and
-split in one direction with a more or less smooth,
-though often irregular, surface. At right angles
-to this surface they break with greater or less
-difficulty and with a frayed edge. As they get
-coarser, the schists may grade into gneisses,
-losing their scaly structure: while on the other
-side, as the constituent minerals become finer
-and so small as to be difficult of recognition,
-schists may grade into slates.</p>
-<div class="pb" id="Page_241">241</div>
-<p>The varieties of schist are based on the mineral
-associated with the quartz; as mica-schist,
-chlorite-schist, hornblende-schist, talc-schist, etc.</p>
-<p>The color also is due to the constituent minerals
-other than quartz and ranges widely, mica-schists
-being white to brown or nearly black,
-chlorite-schists some shade of green, hornblende-schists
-from dark green to black, talc-schists
-white, pale-green, yellowish or gray, etc.</p>
-<p>Schists are found all over the same regions as
-gneisses and quartzites, <i>i.e.</i>, New England
-(especially good exposures of schist being seen
-about New York City), the Lake Superior region,
-Rocky Mountains, etc. Beside these regions
-where it occurs native, there are boulders of
-schist all over the glaciated areas of eastern
-and northern United States.</p>
-<h3><a id="species_Slate">Slate</a></h3>
-<p>Slate is a metamorphic rock which
-will split into thin or thick sheets,
-and is composed of grains so fine as to be indistinguishable
-to the unaided eye. The cleavage
-is the result of pressure during metamorphism,
-and has nothing to do with the bedding or
-stratification of the sedimentary rock from
-which it was derived. The original bedding
-planes may appear as streaks, often more or less
-plicated, and running at any angle with the
-cleavage. If these bedding streaks are abundant
-or very marked, they may make a slate
-unsuitable for commercial uses. The slaty
-cleavage may be very perfect and smooth so
-that the rock splits into fine sheets, in which case
-it is often used for roofing slate; but by far the
-<span class="pb" id="Page_242">242</span>
-greater part of the slates have a cleavage which is
-not smooth or perfect enough so that they can be
-so used. Slates are the metamorphic equivalents
-of shales and muds, and represent the effect of
-great pressure but with less heat than is associated
-with schists or phyllite, and consequently with
-less alteration of the original mineral grains.</p>
-<p>The color ranges from gray through red, green
-and purple to black. The grays and black are due
-to the presence of more or less carbonaceous
-material in the original rock, the carbon compounds
-having changed to graphite. The reds
-and purple are due to the presence of iron oxides,
-and the green to the presence of chlorite.</p>
-<p>While the particles of slate are so small as to
-be indistinguishable to the unaided eye, the use
-of thin sections under the microscope shows that
-slate is composed mostly of quartz and mica,
-with a wide range of accessory minerals, like
-chlorite, feldspar, magnetite, hematite, pyrite,
-calcite, graphite, etc.</p>
-<p>According to their chief constituents slates
-may be distinguished as argillaceous-slate or
-<i>argillite</i>, bituminous-slate, calcareous-slate, siliceous-slate,
-etc.</p>
-<p>Slate will be found here and there in the metamorphic
-areas of New England, the Piedmont
-Plateau, the Lake Superior region, and in many
-places in the west.</p>
-<h3><a id="species_Phyllite">Phyllite</a>
-<br /><a href="#Plate_66">Pl. 66</a></h3>
-<p>Phyllite is a thinly cleavable,
-finely micaceous rock of uniform
-composition, which is intermediate
-between slate and mica schist. In this case the
-<span class="pb" id="Page_243">243</span>
-flakes of mica are large enough to be distinguishable
-to the eye, but most of the rest of the
-material can only be identified with the aid of a
-microscope. It is mostly quartz and sericite.
-Phyllite represents a degree of metamorphism
-greater than for slate, but less than for schist;
-and it may grade into either of these other rocks.
-Garnets, pyrite, etc., may be present as accessory
-minerals. The color ranges from nearly white to
-black, and it is likely to occur in the same places
-as do slates.</p>
-<h3><a id="species_Marble">Marble</a>
-<br /><a href="#Plate_66">Pl. 66</a></h3>
-<p>This is a broad term, and includes
-all those rocks composed essentially
-of calcium carbonate (limestones) or
-its mixture with magnesium carbonate (dolomite),
-which are crystalline, or of granular
-structure, as a result of metamorphism. It
-takes less heat to metamorphose a limestone, and
-for this reason the marbles have a more crystalline
-structure than most metamorphic rocks;
-and they do not have the tendency to split or
-cleave which is so characteristic of most metamorphic
-rocks. It is only when there is a large
-amount of mica present that the typical schistosity
-appears. Commercially the term marble is
-used to include true marble and also those
-limestones which will take a high polish; but in
-this book, and geologically speaking, no rock is a
-marble unless it has crystalline structure.</p>
-<p>Marbles range widely in color according to
-their impurities. Pure marble is white. Carbonaceous
-material in the antecedent limestone
-is changed to graphite in the metamorphic
-<span class="pb" id="Page_244">244</span>
-process, and makes the marble black, but appears
-usually in streaks or spots, rather than in
-any uniform color. An all black &ldquo;marble&rdquo; is usually
-a limestone. The presence of iron colors the
-marble red or pink. Chlorite makes it green, etc.</p>
-<p>Various accessory minerals are common in
-marbles, such as mica, pyroxene, amphibole,
-grossularite among the garnets, magnetite, spinel,
-pyrite, etc., through a long list.</p>
-<p>Because it cuts readily in all directions and
-takes a high polish, marble is widely used as a
-building stone. In the moist climate of the
-United States it suffers in being soluble in rain
-water when used on the outside of a building: but
-for interior decoration it furnishes some of the
-finest effects.</p>
-<p>The largest marble quarries are developed in
-Vermont, Massachusetts, New York, Pennsylvania,
-Georgia, Alabama, Colorado, California,
-and Washington.</p>
-<h3><a id="species_Steatite">Steatite</a>
-<br /><i>Soapstone</i></h3>
-<p>Steatite is a rock composed
-essentially of talc, which is associated
-with more or less impurities,
-such as mica, tremolite, enstatite, quartz,
-magnetite, etc. It is found in and with metamorphic
-rocks, and is a rock which has been
-modified by hydration from a metamorphic
-predecessor. It was probably first a tremolite
-or enstatite schist, in which, after the metamorphic
-rock came into the zone where ground
-water exists, the tremolite or enstatite was
-altered to talc, the impurities remaining much
-as they were in the first place.</p>
-<div class="pb" id="Page_245">245</div>
-<p>It is bluish-gray to green in color, often soft
-enough to cut with a knife, and has a greasy
-feel. It is very resistant to heat and acids; for
-which reasons it has proved very useful commercially
-in making hearthstones, laundry tubs,
-and fire backs; and, when powdered, in making
-certain lubricants. The Indians, in the days
-before Columbus, took advantage of the ease
-with which it is cut, to make from it large pots
-for holding liquids, which are today among the
-greatest treasures in collections of Indian relics.
-They also carved pipe-bowls and various ornaments
-and amulets from soapstone.</p>
-<p>It is found in Vermont, Massachusetts, New
-York, New Jersey, Pennsylvania, Maryland,
-Virginia, North Carolina, Georgia and
-California.</p>
-<h3><a id="species_Serpentine_Rock">Serpentine</a>
-<br /><a href="#Plate_67">Pl. 67</a></h3>
-<p>Pure serpentine is the hydrated
-silicate of magnesium, as described
-among the minerals on <a href="#Page_138">page 138</a>.
-Serpentine rock is serpentine with more or less
-impurities, such as pyroxene, amphibole, olivine,
-magnetite, chromite, calcite, magnesite, etc.
-It often also contains mica and such garnets as
-pyrope, as accessory minerals. Serpentine, like
-steatite, always occurs in and with metamorphic
-rocks, and was originally a metamorphic rock,
-but has since been changed by the hydration of
-its silicates, when it came into the zone in which
-ground water is present. In the first instance it
-was some sort of shale, clay and dolomite, which
-was metamorphosed to an amphibole or pyroxene
-schist. When this was exposed to the action of
-<span class="pb" id="Page_246">246</span>
-ground water, the amphibole or pyroxene minerals
-were changed to serpentine, resulting in a
-rock composed mostly of serpentine, but retaining
-the impurities which were in the metamorphic
-rock, and perhaps adding to them such
-amphiboles and pyroxenes as were not altered
-during the hydration process. The above is
-the commonest type of serpentine rock. It can
-and sometimes has been formed in a similar
-way from an igneous predecessor, by the hydration
-of its silicate minerals. In this latter case
-the serpentine would not be a modified metamorphic
-rock, but a modified igneous one. It is
-a case where such a rock as a diorite or a gabbro
-is exposed to ground water and the pyroxene
-present altered to serpentine. A serpentine
-formed in this way would be a very impure one.</p>
-<p>Serpentine rock is used as an ornamental
-stone for interior decoration, because it takes a
-high polish and has pleasing colors, various
-shades of green. It is however decidedly soft
-and will stand very little exposure to weather,
-and it is also filled with seams which make it
-difficult to get out large slabs.</p>
-<p>Serpentine rock occurs fairly commonly in the
-metamorphic belt of New England and the
-Piedmont Plateau, and in some of the western
-states, especially California, Oregon, and
-Washington.</p>
-<h3><a id="species_Ophiolite">Ophiolite</a>
-<br /><i>Ophicalcite</i></h3>
-<p>This name is given to marbles
-which are streaked and spotted with
-serpentine. They are a mixture of
-green serpentine and a white or nearly white
-<span class="pb" id="Page_247">247</span>
-calcite, magnesite or dolomite in variable
-proportions.</p>
-<p>Ophicalcite occurs in and with metamorphic
-rocks, and represents an impure limestone which
-has been metamorphised, the lime becoming
-marble, and the impurities becoming such silicates
-as pyroxene, amphibole, or olivine. This
-metamorphic rock has then come into the zone
-of ground-water and the silicate minerals have
-been changed by hydration to serpentine. Ophicalcite
-is then a metamorphic rock, in which
-secondary chemical changes have since taken
-place. It may have a wide range of accessory
-minerals present, such as magnetite, chromite,
-pyrope among the garnets, olivine, etc. Verde
-antique is a trade name for one of the ophiolites.</p>
-<p>While not abundant, ophicalcite is in good
-demand as an ornamental stone for interior
-work; for it takes a high polish, and is beautiful;
-but, on the other hand, it will not stand exposure
-to the weather for the calcite is soluble, and there
-are numerous seams and cracks in it making it
-difficult to obtain large slabs.</p>
-<p>It occurs in Quebec, Canada, in the Green
-Mountains of Vermont, and in the Adirondack
-Mountains.</p>
-<div class="pb" id="Page_248">248</div>
-<h2 id="c6"><span class="h2line1">CHAPTER V</span>
-<br /><span class="h2line2">MISCELLANEOUS ROCKS</span></h2>
-<p>There are a few rocks which do not fit into
-any of the three groups described, such as concretions,
-geodes, meteorites, etc., and they are
-gathered together here. There is also one type
-of rock, which really belongs among the minerals,
-but is likely not to be so recognized at first
-glance, and that is the material filling veins.
-These last are sometimes designated &ldquo;vein
-rocks,&rdquo; but are really massive deposits of one,
-two or more minerals, and should be referred
-to the minerals when found.</p>
-<h3 class="center"><span class="sc">Concretions</span></h3>
-<p>In the sedimentary rocks there frequently
-occur inclusions of a nature different from the
-surrounding rock. In shape they are usually
-rounded, nodular, spherical, discoidal, ovate,
-flattened, elongated or ring-shaped, or combinations
-of the foregoing, making often curious and
-fantastic forms. In size they range from a
-fraction of an inch in diameter to several feet
-through. When broken, they may show a
-nucleus, around which more or less concentric
-<span class="pb" id="Page_249">249</span>
-layers have formed, or neither nucleus nor
-concentric structure may be visible. The layered
-structure of the surrounding rock in some cases
-continues right through the nodular mass.
-These structures are called concretions, and
-their formation in all cases is at least due to
-similar reactions.</p>
-<p>In general the concretions differ from the
-surrounding rock in composition, but are usually
-composed of some one of its impurities, of lime
-in the clays or silica in limestones, of iron oxide
-in sandstone, etc. They seem to have originated
-as a result of the solution of the minor mineral,
-and then its redeposition around some center or
-nucleus. In many cases the nucleus is organic,
-such as a leaf, a shell, a bone, etc., so that when
-the concretion is split, in its center will be found
-the perfect imprint of the leaf, or the shell of a
-mollusk, or a bone of a higher animal, sometimes
-a whole skeleton. Again the nucleus may
-be inorganic like a grain of sand; and in still
-other cases no nucleus can be found, though
-there was probably one in the beginning. What
-has happened is somewhat like the case of accessory
-minerals in igneous and metamorphic rocks.
-A layer of sediment was laid down, including in
-it, here and there, something foreign to the run
-of the rock. Later when the water leaches
-through this rock, impregnated with lime for
-instance, it comes to the point where a leaf is
-decomposing. The products of the leaf decomposition
-are different from what is already
-present in solution, and may precipitate some
-of the lime in that neighborhood. As long as leaf
-<span class="pb" id="Page_250">250</span>
-decomposition continues the precipitation in
-that region will continue and increase the size
-of the concretion. This sort of action accounts
-for many of the concretions, especially those
-about organic remains. In some other cases
-where there is no nucleus, as the flint in chalk,
-what has taken place is that the small amounts
-of silica in the lime have been dissolved, and
-then around some center has constantly been
-added more and more non-crystalline silica
-until a mass of flint has accumulated. There
-may be a considerable variety of ways to account
-for different concretions, but in all cases solutions
-of one mineral have come in contact with
-solutions of a different kind, and precipitation
-about a center has resulted.</p>
-<h3><a id="species_ClayStones">Clay stones</a>
-<br /><a href="#Plate_68">Pl. 68</a></h3>
-<p>Of all the concretions these are
-perhaps the commonest, being found
-in the clays of all types and in many
-regions. They are made of lime and precipitated
-around some nucleus of foreign matter. The
-shapes vary widely, usually discs, flattened ovals
-or even rings, in most all cases however flattened.
-This is indicative of the water moving
-though the clay more freely in some layers than
-others. Often clay stones occur so abundantly
-that two or more have grown together making
-fantastic shapes, sometimes resembling animals,
-and all sorts of fancied but unrelated objects.
-As the clay stones have grown the clay has not
-been pushed aside, but has been incorporated
-within the concretion; so that when a concretion
-is dissolved in acid, it yields not only the lime,
-<span class="pb" id="Page_251">251</span>
-which is its reason for being, but also a large
-amount of clay.</p>
-<p>Claystones are found in clays most anywhere,
-usually occurring in certain layers and being
-absent from others.</p>
-<h3><a id="species_LimeConcretions">Lime concretions</a></h3>
-<p>These are found mostly in shales
-which carry a high percentage of
-clay as impurities, and are characteristic
-of the older geological formations, especially
-ancient sea bottoms. They are likely
-to have as a nucleus some shell, fish bone, or a
-leaf, which when the concretion is split, reveals a
-wonderfully preserved portion of an animal or a
-plant, which was buried millions of years ago.
-The lime concretion is closely related to the
-claystone, and is really a claystone which has
-been buried so long that the surrounding matrix
-has changed to a shale instead of remaining
-clay.</p>
-<p>One of the most famous localities for these
-lime concretions is Mazon Creek, Illinois, where
-thousands of these concretions have been picked
-up and split to study the organic remains included.
-The commonest objects found are fern
-leaves, like the one on <a href="#Plate_68">Plate 68</a>. But about once
-in a thousand times they inclose a spider or
-insect, and once in ten thousand times the skeleton
-of an amphibian, which is of especial interest,
-as here have been thus found the remains of the
-very earliest of the land animals. These remains
-were inclosed in these concretions during
-the coal age, probably 50,000,000 years
-ago, and once inclosed all the hard parts have
-<span class="pb" id="Page_252">252</span>
-been as well preserved after that long interval,
-as they were immediately after being inclosed
-in the concretion. Lime concretions range from
-less than an inch in diameter to several feet
-through. They are not confined to shales, but
-sometimes occur in sandstones, in this case also
-usually having as a nucleus either a shell, or the
-bone, or bones, of some animal.</p>
-<p>They are likely to be found anywhere in the
-limestone belt, from the Appalachian Mountains
-to the Rocky Mountains, or in the Great Basin,
-or on the Pacific Coast. Often they have been
-mistaken for turtles and other objects. A good
-many of the cases where the head or body of
-animals &ldquo;petrified with all the flesh&rdquo; are reported,
-it is one of these concretions which has a
-shape sufficiently like the part described, for the
-imagination to construct the rest.</p>
-<h3><a id="species_Septeria">Septeria</a>
-<br /><a href="#Plate_69">Pl. 69</a></h3>
-<p>Septeria are lime concretions,
-which, after they had formed, have
-shrunk and developed a series of
-cracks running through them in all sorts of directions,
-and since then the cracks have been
-filled with various minerals, such as calcite,
-dolomite, and siderite. These make a series of
-veins which intersect the concretion, in a sort of
-network. Septeria are mostly of considerable
-size, ranging from six inches in diameter to
-several feet through. They are characteristic of
-the shales of ancient sea bottoms, especially
-those of Devonian age in New York, and Pennsylvania,
-and those of Cretaceous age in Wyoming,
-Montana and the Dakotas.</p>
-<div class="pb" id="Page_253">253</div>
-<h3><a id="species_FlintConcretions">Flint concretions</a></h3>
-<p>The silica in limestones is often
-segregated into nodular masses of
-varying sizes, to make concretions of
-flint. Such masses have grown in the limestone,
-and, while growing, have either pushed away, or
-dissolved the adjacent limestone, so that the
-flint nodule is pure silica. They are especially
-characteristic of the chalk beds, and of ancient
-limestones which formed on the floor of the sea,
-like the Helderberg Limestone of New York,
-Pennsylvania, Ohio, etc. When thin sections
-are cut through these flints, and examined under
-the microscope, many remnants of the shells of
-plants and animals are still recognizable. A
-nucleus is seldom found, but in some cases there
-is a fossil in the nodule about which the concretion
-doubtless formed. The spicules of sponges,
-shells of diatoms, and of radiolarians seem to
-have contributed most of the material from
-which flint concretions are formed. In addition
-to the silica there are frequently inclosed in these
-nodules the horny jaws of various sea worms,
-and a host of spiny balls the relationships of
-which are still unknown.</p>
-<h3><a id="species_SandstoneConcretions">Sandstone concretions</a></h3>
-<p>There are two types of sandstone
-concretions, first those which are
-cemented with lime, and second
-those cemented with iron oxide. The concretions
-bound by lime are especially characteristic
-of sandstones which were laid down as river
-deposits, either in the channels or on the flood
-plains, and also the sandy deposits resulting
-from wind deposition. In these cases the concretions
-<span class="pb" id="Page_254">254</span>
-will mostly be found to have formed
-around some organic nucleus, most frequently
-about a bone, or group of bones, of some ancient
-animal. In this country they are mostly found
-in the arid and semiarid sections of the West,
-where the present day wind erosion exposes the
-harder parts of bluffs, etc.</p>
-<p>The second type of sandstone concretion is
-the one in which the cement is most often
-limonite, less often hematite. These concretions
-are less dense than the lime ones, and in some
-cases the limonite is only precipitated at a distance
-from the nucleus, which has resulted in the
-formation of a hollow shell, filled with loose
-sand. This is especially characteristic of certain
-concretions, found in a gravel or coarse sand in
-the region of Middletown, Del.</p>
-<h3><a id="species_Oolites">Oolites</a></h3>
-<p>In large bodies of water like the
-sea and some larger lakes we find
-concretions which have formed, or are still
-forming, about tiny grains of sand, which are
-still being moved about by the waves and currents.
-In such cases not only are great masses of
-concretions formed but they have very clearly
-marked the concentric layering, which shows
-that they have increased in size, sometimes more
-rapidly and sometimes more slowly. Where
-great masses of such concretions have formed the
-resulting rock appears like a great mass of small
-eggs, whence the term oolite. The cement may
-be any one of several substances, but lime, silica,
-and hematite are perhaps the most common.
-Here and there are found larger or smaller masses
-<span class="pb" id="Page_255">255</span>
-of this oolite. In some cases it would appear
-that the material was precipitated by the action
-of bacteria. Such for instance is probably the
-origin of the Clinton iron ore, a bed of oolitic
-hematite, extending from New York State all
-down the Appalachian Mountains to Alabama.</p>
-<h3><a id="species_Pisolite">Pisolite</a>
-<br /><a href="#Plate_69">Pl. 69</a></h3>
-<p>When the concretions, formed in
-exactly the same manner as in the
-case of oolite, are of a size bigger
-than a pea, then the rock is known as pisolite.</p>
-<h3 class="center"><span class="sc">Other Concretions</span></h3>
-<p>Though less abundant concretion may form
-from still other substances. Hematite has been
-mentioned, and when concretions are made of
-this material, either they have been deposited by
-bacteria, or were formed as limonite and the
-water of crystallization of this latter mineral
-driven off.</p>
-<p>Manganese concretions are found on the floor
-of the ocean at maximum depths, and brought to
-the surface by dredging.</p>
-<h3 class="center"><span class="sc">Geodes</span></h3>
-<p>Geodes are nodules, which, when broken open,
-are found to be hollow and the cavity lined with
-one or more minerals. They represent a special
-case of minerals in a cave. There was in the
-first place a cavity in the surrounding rock,
-usually of sand or clay. As the water leached
-through the surrounding rock, it became saturated
-<span class="pb" id="Page_256">256</span>
-with one or more minerals and then coming
-into the cavity, deposited the minerals, either as
-crystals, or as a non-crystalline mass, lining the
-cavity. Thus the inside is often a beautiful
-cluster of bristling crystals, or it may be simply
-layer on layer of chalcedony of any color.
-Before this process had gone so far as to completely
-fill the cavity, erosion had dislodged
-the mass, and it has been found. One usually
-recognizes that it is a geode by the fact that it
-is far too light to be a solid rock, and then it
-may be carefully broken. They are characteristic
-of certain formations; so that having accidentally
-broken the first one, others can be
-carefully opened to display the beauty of the
-interior. The geode illustrated on <a href="#Plate_70">Plate 70</a> is
-lined with quartz crystals, but near by were
-found many others, some of which had chalcedony
-and some jasper as a lining. Such crystallined
-nodules are usually called geodes so long
-as they occur in a softer matrix so that they are
-easily dislodged, and until they reach a size of
-three or four feet in diameter.</p>
-<h3 class="center"><span class="sc">Pebbles</span></h3>
-<p>When picked up either from brook beds, sea
-beaches, or the open plain, there are few forms
-of rock which tell a story of the past more completely
-than do pebbles; and any one, who enjoys
-reading a story written in form, structure and
-composition, will find in pebbles one of the most
-satisfying and at the same time testing exercises.
-The story may be complex or simple according
-<span class="pb" id="Page_257">257</span>
-to what has happened to the parent rock, and
-to that is added what happened since the pebble
-left the ledge where it was a part of a great mass.
-One must not forget to take into consideration
-where the pebble was found and the character
-of its associates. This sort of exercise is recommended
-to all interested in rocks. It will yield
-something upon first trying, and more on prolonged
-study; and the fullness with which it is
-done will test one&rsquo;s knowledge of the meaning of
-rocks as nothing else will do. As a sample of this
-sort of exercise let us take the two pebbles illustrated
-on <a href="#Plate_71">Plate 71</a>.</p>
-<p>The upper one is a common quartz pebble
-picked up in a New England brook bed. Such
-pebbles are common all over the country formerly
-covered by the glacial ice sheet. It is crystalline
-quartz, but the individual crystals are not distinguishable,
-and such quartz is typical as the
-filling of veins. It therefore goes back to a time
-when the rocks were fissured, probably in connection
-with the folding accompanying mountain
-making far to the north in Canada. Into
-the fissures thus formed seeped the water which
-had been leaching through the adjacent rocks,
-and it was saturated with silica which it had
-dissolved from those rocks. In the open fissure
-the quartz was deposited as crystals, which
-grew finally filling the fissure and crowding each
-other so that all the faces were obliterated. The
-quartz vein was complete, but it must have been
-far below the surface of the ground. Time must
-have passed, thousands of years of it, until, in
-the weathering away of the mountain system,
-<span class="pb" id="Page_258">258</span>
-the many feet of overlying rock were removed
-and this vein was brought to the surface. As
-the quartz is harder than the adjacent rocks, the
-vein soon projected as a ledge. The effect of
-changes of temperature in alternately expanding
-and contracting the rocks developed cracks, into
-which water worked its way, and then the breaking
-was hastened by the expansion which takes
-place when water freezes, and in exposed regions
-is so effective, because the freezing and thawing
-are so often repeated. Finally an angular
-fragment of quartz was dislodged and lay on the
-surface, resistant to the solvent power of the
-rain. In this case this happened just before the
-advance of the great ice sheet. When that came
-to the place where the fragment lay, it was
-picked up along with all other loose material and
-partly shoved in front of, but probably mostly
-carried frozen in the ice, and journeyed one, two,
-three hundred, perhaps a thousand miles. This
-took many years for the ice moved only a few
-feet a day. Finally however it came to the point
-where the ice melted as fast as it advanced, and
-our quartz fragment was dropped at the front
-of the ice sheet along with other great masses of
-till. Here there was abundant water, partly
-from the melting of the ice, and partly from the
-storms which must develop where there are such
-contrasts in temperature, as there would be over
-the ice, on one hand, and over the bare land in
-front of the ice on the other hand. A torrent
-picked up our fragment and started it on a second
-journey, banging against other stones as it
-rolled along down the stream bed, every time it
-<span class="pb" id="Page_259">259</span>
-struck another stone bruising the corners which
-soon became rounded. Thus from time to time
-during high water the quartz fragment, becoming
-rounder every time it moved, journeyed down
-stream, until it came to the point where the
-stream emptied into a lake. Here the current
-was checked and the stone dropped to the bottom
-along with other larger stones to make the delta
-at the mouth of the stream. There it lay as long
-as the lake existed, and would be lying now,
-but that in New England a tilting movement of
-the land tipped the north end of the lake up and
-the water all ran out. Then the stream began to
-flow over its own delta and in time of freshet
-tore a channel down through the old delta carrying
-the pebble still further down, until it came
-to the level stretch which represented the old
-lake&rsquo;s bottom and there it dropped the pebble
-in its bed. And there it was found and picked
-up to become the pebble which told the above
-story of its life, and to repeat it as often as anyone
-will look at it with a seeing eye.</p>
-<p class="tb">The second pebble is quite a different one.
-It was picked up in a gravel bank along a railroad
-cut, just at the foot of Mt. Toby in Massachussetts,
-and the writer has used it many times
-to test his students, to see if they could read the
-story which it tells.</p>
-<p>It consists of two sorts of rock, the one, angular
-fragments of a hornblende schist, the other,
-a fine-grained granite filling all the spaces between
-the fragments of schist, even in cracks
-less than a quarter of an inch wide. The schist
-<span class="pb" id="Page_260">260</span>
-is the older rock and in its first appearance
-represents a deposit of mud (clay and sand) on
-the floor of the ocean, well out from the shore,
-and somewhere off to the east of Mt. Toby,
-perhaps ten miles, perhaps more, from the place
-where it was found. This was back in early
-Pal&aelig;ozoic times, millions of years ago.</p>
-<p>This deposit was buried by further layers of
-sediment on the sea bottom and cemented into a
-shale. Then during a mountain making period
-the region was folded, and the sediments were
-altered by the combined pressure and heat, our
-layer of rock becoming a hornblende schist.
-After that happened considerable time must have
-passed, but just how much is not indicated by
-the pebble, before another period of disturbance
-took place, during which this deep seated schist
-was faulted, and shattered to fragments along
-the line of breaking. This accounts for the
-angular fragments. Then into the fissure thus
-formed was pressed a molten magma, which while
-liquid enough to flow and be squeezed into every
-opening could not have been very hot; for not
-even the corners of the schist fragments are
-melted or altered, so as to appear any different
-from the mass of the schist. The molten magma
-cooled rather slowly, making a fine-grained
-granite. This must all have taken place far
-below the surface, or the magma would have
-cooled into a felsite or dense lava.</p>
-<p>Again a long time must have elapsed, while
-the rock overlying our piece was eroded away,
-so it could come to the surface. Just about the
-time it did come to the surface, the Connecticut
-<span class="pb" id="Page_261">261</span>
-Valley was formed by a great block, 95 miles
-long by fifteen to twenty miles wide, dropping
-down six or eight thousand feet (probably not
-all at once but by one or two hundred feet at a
-time) between two north and south faults. This
-took place in the Triassic Period. Of course the
-streams then began to wash sand and stones of
-all sizes into the hole. Our pebble was one of
-these. While still an angular fragment, lying
-perhaps ten miles east of the Connecticut Valley,
-a stream started it moving, and as it rolled along
-the brook bed, it was battered and rounded to its
-present shape, and finally tumbled over a waterfall
-to the bottom of the great hole, which had
-been formed as described above. Here with
-other stones it formed part of a coarse gravel,
-coarsest near the sides of the hole, and finer
-toward the middle; for the material was further
-distributed in the bottom of the valley. Our
-stone stayed pretty near the side and was soon
-buried beneath hundreds of feet of similar material.
-The leaching water dissolved enough iron
-rust so that this acted on the lower layers as a
-cement and bound the whole mass into a conglomerate.</p>
-<p>Here for some millions of years our pebble
-rested, while above it was piled sand and gravel
-and a couple of sheets of lava, until the hole was
-filled, and our pebble was near the bottom of the
-mass. Later movements of the land raised the
-whole region, fully six thousand feet, and erosion
-went on for other millions of years. The conglomerate
-and sandstone wore away faster than
-the metamorphosed rocks on either side of the
-<span class="pb" id="Page_262">262</span>
-filled valley, so that a new valley, the present
-Connecticut Valley, came into existence.</p>
-<p>When our pebble finally came near to the
-surface on the side of Mt. Toby (a mound of
-conglomerate which somehow was protected
-and wore down a little less rapidly than the
-conglomerate on either side of it), it was just
-about the time of the glacial period. The great
-ice sheet went over the mountain removing all
-the loose material and some more of the solid
-conglomerate. This brought our pebble to the
-surface, but too late to be moved by the ice.
-However as soon as the ice left the Mt. Toby
-region, the rains fell, and in the further weathering
-of the conglomerate, the cement holding our
-pebble in place was dissolved and it was freed.
-At once a tiny brook started it rolling down the
-side of the mountain, a brook so small that when
-the pebble reached the foot of the slope it did
-not have power to carry it further. Here there
-gathered a fan-shaped mound of such pebbles,
-known as an alluvial fan. It rested here not
-over a couple of thousand years, when the Central
-Vermont R. R. cut a groove through the
-fan, using the material for ballast, and here the
-pebble was found and brought home.</p>
-<h3 class="center"><span class="sc">Meteorites</span></h3>
-<p>Meteorites can hardly be called common, but
-there is always a chance of finding one, and their
-interest is so great, that none should escape
-because unrecognized.</p>
-<div class="pb" id="Page_263">263</div>
-<p>Meteorites are visitors to the earth from space,
-and they bring to us knowledge of the composition
-of planets and solar systems, other than
-our own. It is of interest to note, that while
-they have brought to us some combinations of
-elements which do not occur in the earth, still
-they have not brought any element with which
-we were not already familiar. They are popularly
-known as &ldquo;falling&rdquo; or &ldquo;shooting stars,&rdquo;
-though of course they are not stars, but only
-small masses of matter which are entirely invisible
-until they come inside our atmosphere.</p>
-<p>In space there are many small (compared
-with the size of the earth) chunks of matter, each
-pursuing its solitary way around the sun, or
-wandering through space along paths entirely
-unrelated to the sun. From time to time one of
-these passes near enough to the earth, so as to
-be influenced by its attraction, and then comes
-rushing toward it at tremendous speed, 20 to 30
-miles per second. As soon as it comes into the
-atmosphere, even the very attenuated atmosphere,
-a couple of hundred miles above the
-surface, friction heats the surface of the meteor
-until it glows, and by that light we see the so-called
-shooting star, often with a trail of luminous
-matter streaming out behind. Of course in
-using this term &ldquo;shooting star,&rdquo; we understand
-the meteor is no star, for they are bodies as big
-as our sun, shining at distances billions of miles
-away.</p>
-<p>As the meteor rushes through the atmosphere
-it may all burn up, no large fragment reaching
-the earth&rsquo;s surface. The luminous matter
-<span class="pb" id="Page_264">264</span>
-streaming out behind is material which has
-melted and dripped off the main mass. As this
-oxidizes and cools, that part which did not
-become gaseous will finally fall to the earth as
-fine dust. When however a meteor actually
-falls to the earth, its surface is still hot, though
-probably there has not been time enough for
-much heat to be transmitted to the interior.
-At any rate they do not show any alteration due
-to this cause. On landing and sometimes before
-they land meteors break into two or more pieces.
-When found the surface always shows the effects
-of the heat generated by the friction of passing
-through the air, the surface being smoothed, and
-covered with stream lines and melted out pits
-and hollows, and the outer surface consisting of
-a thin crust, making an appearance, which once
-seen, can hardly be mistaken.</p>
-<p>There are two types of meteorites, those made
-wholly or largely of iron with some nickel, and
-appearing like great chunks of iron, and those
-which are stony and resemble a granite boulder.
-In collections the first sort, <i>i.e.</i> iron meteorites,
-are most abundantly represented, because most
-easily recognized when found. They consist of
-masses of iron and nickel with small amounts of
-other elements, ranging in size from the Cape
-York meteorite, which fell in northern Greenland
-in 1894 and was later brought by Peary to the
-American Museum, and weighs some 36 tons,
-down to small grains as small as a grain of wheat.
-The largest one which has fallen in the United
-States was the Willamette meteorite weighing
-some 15 tons, and falling 19 miles south of Portland,
-<span class="pb" id="Page_265">265</span>
-Oregon. These and all iron meteorites have
-the iron in crystalline form which is readily seen
-if the meteorite is cut, and the surface thus made
-polished, then etched with acid, which is put on
-and quickly washed off. Every meteorite has
-its particular pattern, as illustrated on <a href="#Plate_72">Plate 72</a>,
-and by these patterns can be identified. Meteorites
-have a high value and are eagerly sought by
-certain large institutions and collectors. Since
-the crystalline structure is so characteristic of
-each fall, when a new meteorite is found, it is
-usually cut in two, and one part retained by the
-finder or some institution; while the other part
-is cut into small pieces, an inch or two on a side
-and a quarter of an inch thick, but each large
-enough to show the characteristic pattern.
-These are distributed largely by sale to other
-collectors. Thus a great meteorite collection
-consists of a few large meteorites and a great
-many small portions of other meteorites.</p>
-<p>The second type of meteorite is the stony
-meteorite. Where meteorites have been located
-as they fell and recovered, the majority of them
-were of this type, so that probably more than half
-of the meteorites which fall are of the stony type.
-However when the stony meteorite is exposed to
-weathering it takes only a very short time before
-the surface is eroded off and then such a meteorite
-looks like any other boulder and probably
-most of them fail to be recognized, and so have
-been lost. Because they have so much greater
-variety, they are in many ways of greater interest
-than the iron type.</p>
-<p>It is desirable that every one have his eye out
-<span class="pb" id="Page_266">266</span>
-for meteorites, and when found it is desirable that
-the fact should be reported to some one of the
-great institutions which collect them, such as
-the National Museum in Washington, or the
-American Museum in New York. Each one
-should be on record even if it is desired to keep
-it in a private collection.</p>
-<h3 class="center"><span class="sc">Fossils</span></h3>
-<p>In the sedimentary rocks one is apt to find
-remains of some of the animals and plants that
-lived at the time the rock was forming. While
-the soft parts of animals decompose rapidly,
-shells and bones are likely to be buried in the
-sediments, and if the conditions have been
-favorable, these remains may be preserved more
-or less perfectly. All through the millions of
-years that sedimentary rocks have been forming
-in the sea, in lakes, on river flood plains and in
-wind swept deserts, there was an abundance of
-life, as much as there is today; and our knowledge
-of that life is derived from these buried
-fossil remains, so that fossils have a great historic
-interest.</p>
-<p>However as there have lived and died several
-times as many different kinds of animals as live
-today, the study of fossils becomes a separate
-subject, which cannot be treated in this book.
-Should any collector of rocks and minerals come
-upon fossils, he is opening a new field, and it will
-be necessary to turn to other sources for their
-identification. General books on this subject
-are scarce, but one or two are given in the
-literature list.</p>
-<div class="pb" id="Page_267">267</div>
-<h3 class="center"><span class="sc">A List of the Elements, the Abbreviations Used for Them, and Their Atomic Weight, Which Is Approximately the Number of Times Heavier They Are Than Hydrogen.</span></h3>
-<table class="center" summary="">
-<tr class="th"><th>Name </th><th>Oxygen = 16</th></tr>
-<tr><td class="l">Aluminium, Al </td><td class="r">27</td></tr>
-<tr><td class="l">Antimony, Sb </td><td class="r">122</td></tr>
-<tr><td class="l">Argon, Ar </td><td class="r">40</td></tr>
-<tr><td class="l">Arsenic, As </td><td class="r">75</td></tr>
-<tr><td class="l">Barium, Ba </td><td class="r">137</td></tr>
-<tr><td class="l">Beryllium, Be </td><td class="r">9</td></tr>
-<tr><td class="l">Bismuth, Bi </td><td class="r">209</td></tr>
-<tr><td class="l">Boron, B </td><td class="r">11</td></tr>
-<tr><td class="l">Bromine, Br </td><td class="r">80</td></tr>
-<tr><td class="l">Cadmium, Cd </td><td class="r">112</td></tr>
-<tr><td class="l">C&aelig;sium, Cs </td><td class="r">132</td></tr>
-<tr><td class="l">Calcium, Ca </td><td class="r">40</td></tr>
-<tr><td class="l">Carbon, C </td><td class="r">12</td></tr>
-<tr><td class="l">Cerium, Ce </td><td class="r">140</td></tr>
-<tr><td class="l">Chlorine, Cl </td><td class="r">35</td></tr>
-<tr><td class="l">Chromium, Cr </td><td class="r">52</td></tr>
-<tr><td class="l">Cobalt, Co </td><td class="r">59</td></tr>
-<tr><td class="l">Columbium, Cb </td><td class="r">93</td></tr>
-<tr><td class="l">Copper, Cu </td><td class="r">64</td></tr>
-<tr><td class="l">Dysprosium, Dy </td><td class="r">162</td></tr>
-<tr><td class="l">Erbium, Er </td><td class="r">167</td></tr>
-<tr><td class="l">Europium, Eu </td><td class="r">152</td></tr>
-<tr><td class="l">Fluorine, F </td><td class="r">19</td></tr>
-<tr><td class="l">Gadolinium, Gd </td><td class="r">157</td></tr>
-<tr><td class="l">Gallium, Ga </td><td class="r">70</td></tr>
-<tr><td class="l">Germanium, Ge </td><td class="r">63</td></tr>
-<tr><td class="l">Glucinum, Gl </td><td class="r">9</td></tr>
-<tr><td class="l">Gold, Au </td><td class="r">197</td></tr>
-<tr><td class="l">Hafnium, Hf </td><td class="r">179</td></tr>
-<tr><td class="l">Helium, He </td><td class="r">4</td></tr>
-<tr><td class="l">Holmium, Ho </td><td class="r">165</td></tr>
-<tr><td class="l">Hydrogen, H </td><td class="r">1</td></tr>
-<tr><td class="l">Indium, In </td><td class="r">115</td></tr>
-<tr><td class="l">Iodine, I </td><td class="r">127</td></tr>
-<tr><td class="l">Iridium, Ir </td><td class="r">193</td></tr>
-<tr><td class="l">Iron, Fe </td><td class="r">56</td></tr>
-<tr><td class="l">Krypton, Kr </td><td class="r">84</td></tr>
-<tr><td class="l">Lanthanum, La </td><td class="r">139</td></tr>
-<tr><td class="l">Lead, Pb </td><td class="r">207</td></tr>
-<tr><td class="l">Lithium, Li </td><td class="r">7</td></tr>
-<tr><td class="l">Lutecium, Lu </td><td class="r">175</td></tr>
-<tr><td class="l">Magnesium, Mg </td><td class="r">24</td></tr>
-<tr><td class="l">Manganese, Mn </td><td class="r">55</td></tr>
-<tr><td class="l">Mercury, Hg </td><td class="r">201</td></tr>
-<tr><td class="l">Molybdenum, Mo </td><td class="r">96</td></tr>
-<tr><td class="l">Neodymium, Nd </td><td class="r">144</td></tr>
-<tr><td class="l">Neon, Ne </td><td class="r">20</td></tr>
-<tr><td class="l">Nickel, Ni </td><td class="r">59</td></tr>
-<tr><td class="l">Nitrogen, N </td><td class="r">14</td></tr>
-<tr><td class="l">Osmium, Os </td><td class="r">190</td></tr>
-<tr><td class="l">Oxygen, O </td><td class="r">16</td></tr>
-<tr><td class="l">Palladium, Pd </td><td class="r">107</td></tr>
-<tr><td class="l">Phosphorus, P </td><td class="r">31</td></tr>
-<tr><td class="l">Platinum, Pt </td><td class="r">195</td></tr>
-<tr><td class="l">Potassium, K </td><td class="r">39</td></tr>
-<tr><td class="l">Pr&aelig;seodymium, Pr </td><td class="r">141</td></tr>
-<tr><td class="l">Protoactinium, Pa </td><td class="r">231</td></tr>
-<tr><td class="l">Radium, Ra </td><td class="r">226</td></tr>
-<tr><td class="l">Radon, Rn </td><td class="r">222</td></tr>
-<tr><td class="l">Rhenium, Re </td><td class="r">186</td></tr>
-<tr><td class="l">Rhodium, Rh </td><td class="r">103</td></tr>
-<tr><td class="l">Rubidium, Rb </td><td class="r">85</td></tr>
-<tr><td class="l">Ruthenium, Ru </td><td class="r">102</td></tr>
-<tr><td class="l">Samarium, Sm </td><td class="r">150</td></tr>
-<tr><td class="l">Scandium, Sc </td><td class="r">45</td></tr>
-<tr><td class="l">Selenium, Se </td><td class="r">79</td></tr>
-<tr><td class="l">Silicon, Si </td><td class="r">28</td></tr>
-<tr><td class="l">Silver, Ag </td><td class="r">108</td></tr>
-<tr><td class="l">Sodium, Na </td><td class="r">23</td></tr>
-<tr><td class="l">Strontium, Sr </td><td class="r">88</td></tr>
-<tr><td class="l">Sulphur, S </td><td class="r">32</td></tr>
-<tr><td class="l">Tantalum, Ta </td><td class="r">181</td></tr>
-<tr><td class="l">Tellurium, Te </td><td class="r">128</td></tr>
-<tr><td class="l">Terbium, Tb </td><td class="r">159</td></tr>
-<tr><td class="l">Thallium, Tl </td><td class="r">204</td></tr>
-<tr><td class="l">Thorium, Th </td><td class="r">232</td></tr>
-<tr><td class="l">Thulium, Tu </td><td class="r">169</td></tr>
-<tr><td class="l">Tin, Sn </td><td class="r">119</td></tr>
-<tr><td class="l">Titanium, Ti </td><td class="r">48</td></tr>
-<tr><td class="l">Tungsten, W </td><td class="r">184</td></tr>
-<tr><td class="l">Uranium, U </td><td class="r">238</td></tr>
-<tr><td class="l">Vanadium, V </td><td class="r">51</td></tr>
-<tr><td class="l">Xenon, Xe </td><td class="r">131</td></tr>
-<tr><td class="l">Ytterbium, Yt </td><td class="r">173</td></tr>
-<tr><td class="l">Yttrium, Y </td><td class="r">89</td></tr>
-<tr><td class="l">Zinc, Zn </td><td class="r">65</td></tr>
-<tr><td class="l">Zirconium, Zr </td><td class="r">91</td></tr>
-</table>
-<div class="pb" id="Page_268">268</div>
-<h3 class="center"><span class="sc">Table of Geologic Time</span></h3>
-<table class="center" summary="">
-<tr class="th"><th colspan="3"><i>Eras</i></th></tr>
-<tr class="th"><th> </th><th colspan="2"><i>Periods and their Duration in Millions of Years</i> </th><th> </th><th><i>Important Physical Events</i> </th><th><i>Important Organic Events</i></th></tr>
-<tr><td colspan="3" class="l">Cenozoic</td></tr>
-<tr><td class="l"> </td><td colspan="2" class="l">Quaternary</td></tr>
-<tr><td class="l"> </td><td class="l"> </td><td class="l">Recent </td><td class="r"> </td><td class="l">Youthful land forms having high relief formed. </td><td class="l">Dominance of man.</td></tr>
-<tr><td class="l"> </td><td class="l"> </td><td class="l">Pleistocene Epoch </td><td class="r">2&nbsp;M.Y. </td><td class="l">Period of glaciation; four great ice advances. </td><td class="l">Heidelberg, Neanderthal, and Cr&ocirc;-Magnon man; extinction of large mammals.</td></tr>
-<tr><td class="l"> </td><td colspan="2" class="l">Tertiary</td></tr>
-<tr><td class="l"> </td><td class="l"> </td><td class="l">Pliocene Epoch </td><td class="r">10&nbsp;M.Y. </td><td class="l">Continuing world-wide land elevation. </td><td class="l">Intermigration of North and South American mammals. Transformation of ape to man.</td></tr>
-<tr><td class="l"> </td><td class="l"> </td><td class="l">Miocene Epoch </td><td class="r">18&nbsp;M.Y. </td><td class="l">Cordilleras, Alps, Himalayas formed. Widespread vulcanism-basalt flows in northwestern United States. </td><td class="l">Culmination of modern types of mammals. Apes appear in Old World.</td></tr>
-<tr><td class="l"> </td><td class="l"> </td><td class="l">Oligocene Epoch </td><td class="r">10&nbsp;M.Y. </td><td class="l">Land dominant; seas marginal. </td><td class="l">Carnivores and ungulates develop into importance.</td></tr>
-<tr><td class="l"> </td><td class="l"> </td><td class="l">Eocene Epoch </td><td class="r">20&nbsp;M.Y. </td><td class="l">Extensive sedimentation; seas marginal. </td><td class="l">Dawn of the dominance of mammals. Reptiles subordinate.</td></tr>
-<tr><td colspan="3" class="l">Cretaceous </td><td class="r">65&nbsp;M.Y. </td><td class="l">Widespread epicontinental seas. Laramide revolution at close of period&mdash;Rocky Mountains formed. </td><td class="l">Climax and culmination of reptiles, especially dinosaurs; first flowering plants and grasses.</td></tr>
-<tr class="pbtr"><td colspan="6">
-</td></tr>
-<tr><td colspan="3" class="l">Mesozoic</td></tr>
-<tr><td class="l"> </td><td colspan="2" class="l">Jurassic </td><td class="r">38&nbsp;M.Y. </td><td class="l">Continent emergent; shallow seas on western North America. </td><td class="l">Rise of birds and flying reptiles, first modern trees.</td></tr>
-<tr><td class="l"> </td><td colspan="2" class="l">Triassic </td><td class="r">35&nbsp;M.Y. </td><td class="l">Continent emergent; seas marginal. </td><td class="l">Rise of dinosaurs, cycads, and ammonites.</td></tr>
-<tr><td colspan="3" class="l">Paleozoic</td></tr>
-<tr><td class="l"> </td><td colspan="2" class="l">Permian </td><td class="r">35&nbsp;M.Y. </td><td class="l">World-wide continental uplift and mountain building. Widespread glaciation. </td><td class="l">Extinction of most Paleozoic fauna and flora. First modern insects.</td></tr>
-<tr><td class="l"> </td><td colspan="2" class="l">Pennsylvanian </td><td class="r">48&nbsp;M.Y. </td><td class="l">Continent alternately rising and sinking. </td><td class="l">Great coal-forming forests, of ferns and seed-ferns.</td></tr>
-<tr><td class="l"> </td><td colspan="2" class="l">Mississippian </td><td class="r">35&nbsp;M.Y. </td><td class="l">Low lands and widespread submergence. </td><td class="l">Culmination of crinoids, numerous sharks.</td></tr>
-<tr><td class="l"> </td><td colspan="2" class="l">Devonian </td><td class="r">40&nbsp;M.Y. </td><td class="l">Widespread submergence, local vulcanism. </td><td class="l">First known land animals, first forests.</td></tr>
-<tr><td class="l"> </td><td colspan="2" class="l">Silurian </td><td class="r">28&nbsp;M.Y. </td><td class="l">Widespread submergence, local deserts. </td><td class="l">First lung fishes and scorpions, abundant corals.</td></tr>
-<tr><td class="l"> </td><td colspan="2" class="l">Ordovician </td><td class="r">65&nbsp;M.Y. </td><td class="l">60% of North America below sea. </td><td class="l">Climax of invertebrate dominance, first vertebrate.</td></tr>
-<tr><td class="l"> </td><td colspan="2" class="l">Cambrian </td><td class="r">105&nbsp;M.Y. </td><td class="l">Widespread submergence. </td><td class="l">First abundant invertebrate fauna, trilobites dominant.</td></tr>
-<tr><td colspan="3" class="l">Proterozoic </td><td class="r">700&nbsp;&plusmn;&nbsp;M.Y. </td><td class="l">Long periods of granite intrusion, sedimentation, and mountain building. </td><td class="l">Bacteria and seaweeds present. Most invertebrates probably present, but remains are lacking.</td></tr>
-<tr><td colspan="3" class="l">Archeozoic </td><td class="r">800&nbsp;&plusmn;&nbsp;M.Y. </td><td class="l">World-wide intrusive igneous activity; some sediments. </td><td class="l">Blue-green algae present, primitive one-celled plants and animals probably present.</td></tr>
-</table>
-<div class="pb" id="Page_270">270</div>
-<h2 id="c7"><span class="h2line1">BIBLIOGRAPHY</span></h2>
-<h3 class="biblio">MINERALOGY</h3>
-<p class="biblio"><i>Getting Acquainted with Mineralogy.</i> By G. L. English,
-1936, McGraw-Hill Book Co. A beginning textbook
-of mineralogy.</p>
-<p class="biblio"><i>Introduction to the Study of Minerals and Rocks.</i> 3rd
-Edition, by A. F. Rogers, 1937, McGraw-Hill Book
-Co. Describes the commoner minerals systematically.</p>
-<p class="biblio"><i>Dana&rsquo;s Textbook of Mineralogy.</i> 4th Edition, revised by
-W. E. Ford, 1932, John Wiley and Sons. Detailed
-descriptions of minerals, their physical properties, and
-their occurrence.</p>
-<p class="biblio"><i>Manual of Mineralogy.</i> 15th Edition, by E. S. Dana, revised
-by C. S. Hurlburt, 1941, John Wiley and Sons.
-A textbook of mineralogy.</p>
-<h3 class="biblio">MINERAL ECONOMICS, GEOPOLITICS</h3>
-<p class="biblio"><i>World Minerals and World Peace.</i> By C. K. Leith, J. W.
-Furness, and Cleona Lewis, 1943, The Brookings Institution.
-Physical, economic, and political trends in
-the mineral industry.</p>
-<p class="biblio"><i>Minerals in World Affairs.</i> By T. S. Lovering, 1943,
-Prentice-Hall.</p>
-<p class="biblio"><i>Minerals Yearbook.</i> U. S. Bureau of Mines. An annual
-volume presenting statistical data on the production
-of the mineral resources of the United States. Reports
-on individual minerals or rocks may be had
-separately.</p>
-<h3 class="biblio">ECONOMIC GEOLOGY</h3>
-<p class="biblio"><i>Mineral Deposits.</i> 4th Edition, by W. Lindgren, 1933,
-McGraw-Hill Book Co. The manner of occurrence
-and origin of mineral deposits.</p>
-<p class="biblio"><i>Elements of Engineering Geology.</i> 2nd Edition, by H.
-Ries and T. L. Watson, 1947, John Wiley and Sons.</p>
-<p class="biblio"><i>This Fascinating Oil Business.</i> By M. W. Ball, 1940,
-Bobbs-Merrill Co. A simple and elementary description
-of the petroleum industry.</p>
-<p class="biblio"><i>Geology of Coal.</i> By O. Stutzer and A. C. Noe, 1940,
-University of Chicago Press.</p>
-<h3 class="biblio">GENERAL GEOLOGY</h3>
-<p class="biblio"><i>Down to Earth.</i> By C. Croneis and W. C. Krumbein,
-1936, University of Chicago Press. An introduction
-to geology, profusely illustrated.</p>
-<div class="pb" id="Page_271">271</div>
-<p class="biblio"><i>Textbook of Geology Part I&mdash;Physical Geology.</i> 4th Edition,
-by C. R. Longwell, A. Knopf, and R. F. Flint,
-1939, John Wiley and Sons. A standard text on
-geology.</p>
-<p class="biblio"><i>Field Geology.</i> 4th Edition, by F. H. Lahee, 1941,
-McGraw-Hill Book Co. Recognition and interpretation
-of geologic structures and topographic forms as
-they are observed, and methods of geologic work.</p>
-<h3 class="biblio">PRECIOUS STONES</h3>
-<p class="biblio"><i>A Book of Precious Stones.</i> By J. Wodiska, 1910, G. P.
-Putnam&rsquo;s Sons. Written for jewelers, but of general
-interest.</p>
-<p class="biblio"><i>The Curious Lore of Precious Stones.</i> By G. F. Kunz,
-1913, Lippincott. Legends and stories of the gem
-minerals.</p>
-<p class="biblio"><i>The Magic of Jewels and Charms.</i> By G. F. Kunz, 1915,
-Lippincott.</p>
-<p class="biblio"><i>Popular Gemology.</i> By R. M. Pearl, 1948, John Wiley
-and Sons. Scientific and industrial uses of gems,
-current information about their locality and production.</p>
-<h3 class="biblio">FOSSILS</h3>
-<p class="biblio"><i>An Introduction to the Study of Fossils.</i> By H. W.
-Shimer, 1933, Macmillan Co. An introductory textbook
-about fossil plants and animals.</p>
-<p class="biblio"><i>Invertebrate Paleontology.</i> By W. H. Twenhofel and R.
-P. Shrock, 1935, McGraw-Hill Book Co.</p>
-<p class="biblio"><i>Textbook of Geology Part II&mdash;Historical Geology.</i> 4th
-Edition, by C. Schuchert and C. O. Dunbar, 1941,
-John Wiley and Sons. The story of the development
-of life through the ages.</p>
-<div class="pb" id="Page_273">273</div>
-<h2 id="c8"><span class="h2line1">INDEX</span></h2>
-<p class="center"><a href="#index_A" class="ab">A</a> <a href="#index_B" class="ab">B</a> <a href="#index_C" class="ab">C</a> <a href="#index_D" class="ab">D</a> <a href="#index_E" class="ab">E</a> <a href="#index_F" class="ab">F</a> <a href="#index_G" class="ab">G</a> <a href="#index_H" class="ab">H</a> <a href="#index_I" class="ab">I</a> <a href="#index_J" class="ab">J</a> <a href="#index_K" class="ab">K</a> <a href="#index_L" class="ab">L</a> <a href="#index_M" class="ab">M</a> <a href="#index_N" class="ab">N</a> <a href="#index_O" class="ab">O</a> <a href="#index_P" class="ab">P</a> <a href="#index_Q" class="ab">Q</a> <a href="#index_R" class="ab">R</a> <a href="#index_S" class="ab">S</a> <a href="#index_T" class="ab">T</a> <a href="#index_U" class="ab">U</a> <a href="#index_V" class="ab">V</a> <a href="#index_W" class="ab">W</a> <a href="#index_X" class="ab">X</a> <span class="ab">Y</span> <a href="#index_Z" class="ab">Z</a></p>
-<dl class="index">
-<dt class="center b" id="index_A">A</dt>
-<dt>Actinolite, <a href="#Page_120">120</a></dt>
-<dt>Adobe, <a href="#Page_210">210</a></dt>
-<dt>Agate, <a href="#Page_107">107</a></dt>
-<dt>Agate, moss, <a href="#Page_73">73</a>, <a href="#Page_108">108</a></dt>
-<dt>Alabaster, <a href="#Page_152">152</a></dt>
-<dt>Albertite, <a href="#Page_229">229</a></dt>
-<dt>Albite, <a href="#Page_110">110</a>, <a href="#Page_113">113</a>, <a href="#Page_115">115</a></dt>
-<dt>Almandine, <a href="#Page_97">97</a></dt>
-<dt>Almandite, <a href="#Page_122">122</a>, <a href="#Page_123">123</a></dt>
-<dt>Aluminum bronze, <a href="#Page_74">74</a></dt>
-<dt>Aluminum group, <a href="#Page_73">73</a></dt>
-<dt>Amazon stone, <a href="#Page_114">114</a></dt>
-<dt>Amber, <a href="#Page_223">223</a></dt>
-<dt>Amethyst, <a href="#Page_104">104</a></dt>
-<dt>Amethyst, Oriental, <a href="#Page_75">75</a></dt>
-<dt>Amianthus, <a href="#Page_120">120</a></dt>
-<dt>Amphibole group, <a href="#Page_119">119</a></dt>
-<dt>Amygdoloid, <a href="#Page_194">194</a></dt>
-<dt>Amygdoloidal, <a href="#Page_176">176</a></dt>
-<dt>Analcite, <a href="#Page_141">141</a></dt>
-<dt>Andesite, <a href="#Page_113">113</a>, <a href="#Page_187">187</a></dt>
-<dt>Andradite, <a href="#Page_122">122</a>, <a href="#Page_124">124</a></dt>
-<dt>Anglesite, <a href="#Page_62">62</a></dt>
-<dt>Anhydrite, <a href="#Page_149">149</a></dt>
-<dt>Anorthite, <a href="#Page_110">110</a>, <a href="#Page_113">113</a></dt>
-<dt>Anorthosite, <a href="#Page_183">183</a></dt>
-<dt>Anthracite, <a href="#Page_218">218</a>, <a href="#Page_222">222</a></dt>
-<dt>Antimony, <a href="#Page_81">81</a></dt>
-<dt>Antimony, gray, <a href="#Page_81">81</a></dt>
-<dt>Apatite, <a href="#Page_160">160</a></dt>
-<dt>Aquamarine, <a href="#Page_125">125</a></dt>
-<dt>Aragonite, <a href="#Page_147">147</a></dt>
-<dt>Argentite, <a href="#Page_35">35</a></dt>
-<dt>Argillite, <a href="#Page_242">242</a></dt>
-<dt>Arkose, <a href="#Page_206">206</a></dt>
-<dt>Arsenic group, <a href="#Page_78">78</a></dt>
-<dt>Arsenopyrite, <a href="#Page_79">79</a></dt>
-<dt>Asbestos, <a href="#Page_120">120</a>, <a href="#Page_140">140</a></dt>
-<dt>Augite, <a href="#Page_118">118</a></dt>
-<dt>Aventurine, <a href="#Page_104">104</a></dt>
-<dt>Azurite, <a href="#Page_46">46</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_B">B</dt>
-<dt>Barite, <a href="#Page_154">154</a></dt>
-<dt>Barium group, <a href="#Page_154">154</a></dt>
-<dt>Basalt, <a href="#Page_188">188</a></dt>
-<dt>Batholith, <a href="#Page_174">174</a></dt>
-<dt>Bauxite, <a href="#Page_77">77</a></dt>
-<dt>Beryl, <a href="#Page_125">125</a></dt>
-<dt>Beryl, golden, <a href="#Page_125">125</a></dt>
-<dt>Beryllium, <a href="#Page_125">125</a></dt>
-<dt>Bibliography, <a href="#Page_270">270</a></dt>
-<dt>Biotite, <a href="#Page_129">129</a>, <a href="#Page_130">130</a></dt>
-<dt>Bitumen, <a href="#Page_228">228</a></dt>
-<dt>Black jack, <a href="#Page_65">65</a></dt>
-<dt>Bloodstone, <a href="#Page_106">106</a></dt>
-<dt>Bog lime, <a href="#Page_213">213</a></dt>
-<dt>Bombs, <a href="#Page_191">191</a></dt>
-<dt>Boracite, <a href="#Page_164">164</a></dt>
-<dt>Borax, <a href="#Page_165">165</a></dt>
-<dt>Bornite, <a href="#Page_41">41</a></dt>
-<dt>Brass, <a href="#Page_64">64</a></dt>
-<dt>Breccia, <a href="#Page_191">191</a>, <a href="#Page_198">198</a></dt>
-<dt>Brittania metal, <a href="#Page_81">81</a></dt>
-<dt>Bronze, <a href="#Page_38">38</a></dt>
-<dt>Bronze Age, <a href="#Page_38">38</a></dt>
-<dt>Bronzite, <a href="#Page_118">118</a></dt>
-<dt>Bytownite, <a href="#Page_113">113</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_C">C</dt>
-<dt>Calamine, <a href="#Page_68">68</a></dt>
-<dt>Calaverite, <a href="#Page_30">30</a></dt>
-<dt>Calcite, <a href="#Page_144">144</a></dt>
-<dt>Calcium, <a href="#Page_143">143</a></dt>
-<dt>Carbon, <a href="#Page_156">156</a></dt>
-<dt>Carbonite, <a href="#Page_222">222</a></dt>
-<dt>Carbuncle, <a href="#Page_124">124</a></dt>
-<dt>Carnelian, <a href="#Page_106">106</a></dt>
-<dt>Carnotite, <a href="#Page_90">90</a></dt>
-<dt>Cassiterite, <a href="#Page_93">93</a></dt>
-<dt>Cat&rsquo;s eye, <a href="#Page_104">104</a></dt>
-<dt>Celestite, <a href="#Page_153">153</a></dt>
-<dt>Cerargyrite, <a href="#Page_37">37</a></dt>
-<dt>Cerrusite, <a href="#Page_61">61</a></dt>
-<dt>Ceylonite, <a href="#Page_97">97</a></dt>
-<dt class="pb" id="Page_274">274</dt>
-<dt>Chalcedony, <a href="#Page_104">104</a>, <a href="#Page_106">106</a></dt>
-<dt>Chalcocite, <a href="#Page_42">42</a></dt>
-<dt>Chalcopyrite, <a href="#Page_40">40</a></dt>
-<dt>Chalcotrichite, <a href="#Page_45">45</a></dt>
-<dt>Chalk, <a href="#Page_213">213</a></dt>
-<dt>Chert, <a href="#Page_107">107</a></dt>
-<dt>Chlorite, <a href="#Page_140">140</a></dt>
-<dt>Chlorospinel, <a href="#Page_98">98</a></dt>
-<dt>Chromite, <a href="#Page_87">87</a></dt>
-<dt>Chromium, <a href="#Page_86">86</a></dt>
-<dt>Chrysocola, <a href="#Page_47">47</a></dt>
-<dt>Chrysolite, <a href="#Page_134">134</a>, <a href="#Page_140">140</a></dt>
-<dt>Chrysoprase, <a href="#Page_106">106</a></dt>
-<dt>Cinnabar, <a href="#Page_91">91</a></dt>
-<dt>Cinnamon stone, <a href="#Page_123">123</a></dt>
-<dt>Citrine, <a href="#Page_103">103</a></dt>
-<dt>Clay, <a href="#Page_207">207</a></dt>
-<dt>Clay, ball, <a href="#Page_208">208</a></dt>
-<dt>Clay, brick, <a href="#Page_209">209</a></dt>
-<dt>Clay, china, <a href="#Page_208">208</a></dt>
-<dt>Clay, fire, <a href="#Page_208">208</a></dt>
-<dt>Clay, paving brick, <a href="#Page_209">209</a></dt>
-<dt>Clay, sewer-pipe, <a href="#Page_209">209</a></dt>
-<dt>Clay, slip, <a href="#Page_209">209</a></dt>
-<dt>Clay, stoneware, <a href="#Page_209">209</a></dt>
-<dt>Clay stones, <a href="#Page_250">250</a></dt>
-<dt>Cleavage, <a href="#Page_21">21</a></dt>
-<dt>Cleavage, slaty, <a href="#Page_234">234</a></dt>
-<dt>Coal, <a href="#Page_217">217</a></dt>
-<dt>Coal, bituminous, <a href="#Page_212">212</a>, <a href="#Page_220">220</a></dt>
-<dt>Coal, cannel, <a href="#Page_221">221</a></dt>
-<dt>Coal, hard, <a href="#Page_222">222</a></dt>
-<dt>Coal, soft, <a href="#Page_220">220</a></dt>
-<dt>Cobalt, <a href="#Page_84">84</a></dt>
-<dt>Cobalt bloom, <a href="#Page_85">85</a></dt>
-<dt>Cobalt glance, <a href="#Page_85">85</a></dt>
-<dt>Cobalt gray ore, <a href="#Page_85">85</a></dt>
-<dt>Cobaltite, <a href="#Page_83">83</a></dt>
-<dt>Coke, <a href="#Page_220">220</a></dt>
-<dt>Colemanite, <a href="#Page_165">165</a></dt>
-<dt>Collecting, <a href="#Page_5">5</a>, <a href="#Page_7">7</a></dt>
-<dt>Color, <a href="#Page_23">23</a></dt>
-<dt>Concretions, <a href="#Page_248">248</a></dt>
-<dt>Concretions, flint, <a href="#Page_253">253</a></dt>
-<dt>Concretions, lime, <a href="#Page_251">251</a></dt>
-<dt>Concretions, other, <a href="#Page_255">255</a></dt>
-<dt>Concretions, sandstone, <a href="#Page_253">253</a></dt>
-<dt>Conglomerate, <a href="#Page_202">202</a></dt>
-<dt>Copper, <a href="#Page_37">37</a>, <a href="#Page_39">39</a></dt>
-<dt>Copper, blushing, <a href="#Page_42">42</a></dt>
-<dt>Copper, glance, <a href="#Page_42">42</a></dt>
-<dt>Copper, grey, <a href="#Page_43">43</a></dt>
-<dt>Copper, peacock, <a href="#Page_42">42</a></dt>
-<dt>Copper, plush, <a href="#Page_45">45</a></dt>
-<dt>Copper, purple, <a href="#Page_41">41</a></dt>
-<dt>Copper, red, <a href="#Page_44">44</a></dt>
-<dt>Copper, variegated, <a href="#Page_42">42</a></dt>
-<dt>Copper, yellow, <a href="#Page_40">40</a></dt>
-<dt>Coquina, <a href="#Page_213">213</a></dt>
-<dt>Coral, <a href="#Page_146">146</a></dt>
-<dt>Coral rock, <a href="#Page_214">214</a></dt>
-<dt>Corundum, <a href="#Page_75">75</a></dt>
-<dt>Crude oil, <a href="#Page_227">227</a></dt>
-<dt>Cryolite, <a href="#Page_78">78</a></dt>
-<dt>Crystal balls, <a href="#Page_101">101</a></dt>
-<dt>Crystal formation, <a href="#Page_14">14</a></dt>
-<dt>Crystal rock, <a href="#Page_103">103</a></dt>
-<dt>Crystal structure, <a href="#Page_11">11</a></dt>
-<dt>Crystal systems, <a href="#Page_13">13</a>-18</dt>
-<dt>Cuprite, <a href="#Page_44">44</a></dt>
-<dt>Cyanite, <a href="#Page_128">128</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_D">D</dt>
-<dt>Dacite, <a href="#Page_187">187</a></dt>
-<dt>Dense, <a href="#Page_176">176</a></dt>
-<dt>Diamond, <a href="#Page_157">157</a></dt>
-<dt>Diamonds, Matura, <a href="#Page_127">127</a></dt>
-<dt>Diamonds, slave&rsquo;s, <a href="#Page_133">133</a></dt>
-<dt>Diatoms, <a href="#Page_231">231</a></dt>
-<dt>Dikes, <a href="#Page_174">174</a></dt>
-<dt>Diorite, <a href="#Page_182">182</a></dt>
-<dt>Dog-tooth spar, <a href="#Page_145">145</a></dt>
-<dt>Dolomite, <a href="#Page_99">99</a></dt>
-<dt>Dry bone, <a href="#Page_68">68</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_E">E</dt>
-<dt>Earth, diatomaceous, <a href="#Page_23">23</a></dt>
-<dt>Elements, listed, <a href="#Page_267">267</a></dt>
-<dt>Emerald, <a href="#Page_125">125</a></dt>
-<dt>Emerald, Oriental, <a href="#Page_75">75</a></dt>
-<dt>Emery, <a href="#Page_76">76</a></dt>
-<dt>Enstatite, <a href="#Page_117">117</a></dt>
-<dt>Epidote, <a href="#Page_134">134</a></dt>
-<dt>Equipment, <a href="#Page_7">7</a></dt>
-<dt>Erubescite, <a href="#Page_42">42</a></dt>
-<dt>Extrusive, <a href="#Page_173">173</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_F">F</dt>
-<dt>Feldspar, <a href="#Page_110">110</a></dt>
-<dt>Feldspar, alkalic, <a href="#Page_111">111</a></dt>
-<dt>Felsite, <a href="#Page_186">186</a></dt>
-<dt>Felsitic, <a href="#Page_176">176</a></dt>
-<dt>Ferromanganese, <a href="#Page_70">70</a></dt>
-<dt>Flagstone, <a href="#Page_207">207</a></dt>
-<dt>Flint, <a href="#Page_106">106</a></dt>
-<dt class="pb" id="Page_275">275</dt>
-<dt>Fluorine, <a href="#Page_162">162</a></dt>
-<dt>Fluorite, <a href="#Page_162">162</a></dt>
-<dt>Fossils, <a href="#Page_266">266</a></dt>
-<dt>Fragmental, <a href="#Page_176">176</a></dt>
-<dt>Franklinite, <a href="#Page_69">69</a></dt>
-<dt>Freestone, <a href="#Page_207">207</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_G">G</dt>
-<dt>Gabbro, <a href="#Page_183">183</a></dt>
-<dt>Galena, <a href="#Page_60">60</a></dt>
-<dt>Garnet group, <a href="#Page_121">121</a></dt>
-<dt>Garnet, Sirian, <a href="#Page_123">123</a></dt>
-<dt>Geodes, <a href="#Page_255">255</a></dt>
-<dt>German silver, <a href="#Page_82">82</a></dt>
-<dt>Gilsonite, <a href="#Page_229">229</a></dt>
-<dt>Glassy, <a href="#Page_176">176</a></dt>
-<dt>Glucinum, <a href="#Page_125">125</a></dt>
-<dt>Gneiss, <a href="#Page_237">237</a></dt>
-<dt>Goethite, <a href="#Page_51">51</a>, <a href="#Page_52">52</a></dt>
-<dt>Gold, <a href="#Page_31">31</a></dt>
-<dt>Gold foil, <a href="#Page_64">64</a></dt>
-<dt>Gold group, <a href="#Page_29">29</a></dt>
-<dt>Gossan, <a href="#Page_50">50</a></dt>
-<dt>Granite, <a href="#Page_178">178</a></dt>
-<dt>Granite, graphic, <a href="#Page_179">179</a></dt>
-<dt>Granitoid, <a href="#Page_176">176</a></dt>
-<dt>Graphite, <a href="#Page_156">156</a>, <a href="#Page_219">219</a></dt>
-<dt>Gravel, <a href="#Page_201">201</a></dt>
-<dt>Graywacke, <a href="#Page_206">206</a></dt>
-<dt>Grit, <a href="#Page_206">206</a></dt>
-<dt>Grossularite, <a href="#Page_122">122</a>, <a href="#Page_123">123</a></dt>
-<dt>Guano, <a href="#Page_230">230</a></dt>
-<dt>Gumbo, <a href="#Page_210">210</a></dt>
-<dt>Gypsum, <a href="#Page_150">150</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_H">H</dt>
-<dt>Halite, <a href="#Page_163">163</a></dt>
-<dt>Hardness, <a href="#Page_20">20</a></dt>
-<dt>Hardpan, <a href="#Page_216">216</a></dt>
-<dt>Heavy spar, <a href="#Page_154">154</a></dt>
-<dt>Heliotrope, <a href="#Page_106">106</a></dt>
-<dt>Hematite, <a href="#Page_53">53</a></dt>
-<dt>Hemihedral forms, <a href="#Page_19">19</a></dt>
-<dt>Hercynite, <a href="#Page_98">98</a></dt>
-<dt>Hexagonal system, <a href="#Page_18">18</a></dt>
-<dt>Hornblende, <a href="#Page_121">121</a></dt>
-<dt>Hornstone, <a href="#Page_107">107</a></dt>
-<dt>Hyacinth, <a href="#Page_127">127</a></dt>
-<dt>Hypersthene, <a href="#Page_118">118</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_I">I</dt>
-<dt>Ice, <a href="#Page_167">167</a></dt>
-<dt>Iceland spar, <a href="#Page_145">145</a></dt>
-<dt>Ice stone, <a href="#Page_78">78</a></dt>
-<dt>Ilmenite, <a href="#Page_94">94</a></dt>
-<dt>Intrusive, <a href="#Page_174">174</a></dt>
-<dt>Iron, <a href="#Page_47">47</a></dt>
-<dt>Iron, bog, <a href="#Page_50">50</a></dt>
-<dt>Iron, chromic, <a href="#Page_87">87</a></dt>
-<dt>Iron, magnetic, <a href="#Page_54">54</a></dt>
-<dt>Iron pyrites, <a href="#Page_56">56</a></dt>
-<dt>Iron, spathic, <a href="#Page_55">55</a></dt>
-<dt>Iron, specular, <a href="#Page_53">53</a></dt>
-<dt>Isometric system, <a href="#Page_13">13</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_J">J</dt>
-<dt>Jacinth, <a href="#Page_127">127</a></dt>
-<dt>Jargons, <a href="#Page_127">127</a></dt>
-<dt>Jargoons, <a href="#Page_127">127</a></dt>
-<dt>Jasper, <a href="#Page_106">106</a></dt>
-<dt>Jet, <a href="#Page_222">222</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_K">K</dt>
-<dt>Kaolin, <a href="#Page_137">137</a>, <a href="#Page_208">208</a></dt>
-<dt>Kaolinite, <a href="#Page_137">137</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_L">L</dt>
-<dt>Labels, <a href="#Page_5">5</a></dt>
-<dt>Labradorite, <a href="#Page_113">113</a>, <a href="#Page_116">116</a></dt>
-<dt>Laccolith, <a href="#Page_174">174</a></dt>
-<dt>Lapilli, <a href="#Page_191">191</a></dt>
-<dt>Lava, <a href="#Page_173">173</a></dt>
-<dt>Lead, <a href="#Page_59">59</a></dt>
-<dt>Lead glance, <a href="#Page_60">60</a></dt>
-<dt>Lead, green ore, <a href="#Page_63">63</a></dt>
-<dt>Lead, white ore, <a href="#Page_61">61</a></dt>
-<dt>Lepidolite, <a href="#Page_129">129</a>, <a href="#Page_130">130</a></dt>
-<dt>Lignite, <a href="#Page_218">218</a>, <a href="#Page_219">219</a></dt>
-<dt>Limestone, <a href="#Page_212">212</a></dt>
-<dt>Limestone, encrinal, <a href="#Page_214">214</a></dt>
-<dt>Limestone, hydraulic, <a href="#Page_214">214</a></dt>
-<dt>Limestone, lithographic, <a href="#Page_214">214</a></dt>
-<dt>Limonite, <a href="#Page_49">49</a>, <a href="#Page_51">51</a></dt>
-<dt>Loess, <a href="#Page_210">210</a></dt>
-<dt>Luster, <a href="#Page_23">23</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_M">M</dt>
-<dt>Magma, <a href="#Page_173">173</a></dt>
-<dt>Magnesite, <a href="#Page_98">98</a></dt>
-<dt>Magnesium group, <a href="#Page_96">96</a></dt>
-<dt>Magnetite, <a href="#Page_54">54</a></dt>
-<dt>Malachite, <a href="#Page_45">45</a></dt>
-<dt>Malanite, <a href="#Page_124">124</a></dt>
-<dt>Malta, <a href="#Page_229">229</a></dt>
-<dt>Manganese group, <a href="#Page_70">70</a></dt>
-<dt>Manganite, <a href="#Page_72">72</a></dt>
-<dt>Marble, <a href="#Page_243">243</a></dt>
-<dt>Marble, Suisun, <a href="#Page_146">146</a></dt>
-<dt class="pb" id="Page_276">276</dt>
-<dt>Marcasite, <a href="#Page_57">57</a></dt>
-<dt>Marl, <a href="#Page_211">211</a></dt>
-<dt>Mercury, <a href="#Page_90">90</a></dt>
-<dt>Meteorites, <a href="#Page_262">262</a></dt>
-<dt>Mica group, <a href="#Page_128">128</a></dt>
-<dt>Microcline, <a href="#Page_113">113</a>, <a href="#Page_114">114</a></dt>
-<dt>Millerite, <a href="#Page_83">83</a></dt>
-<dt>Mineral tables, <a href="#Page_25">25</a></dt>
-<dt>Minerals, defined, <a href="#Page_10">10</a></dt>
-<dt>Molybdenite, <a href="#Page_81">81</a></dt>
-<dt>Molybdenum, <a href="#Page_80">80</a></dt>
-<dt>Monoclinic system, <a href="#Page_17">17</a></dt>
-<dt>Monzonite, <a href="#Page_181">181</a></dt>
-<dt>Morion, <a href="#Page_103">103</a></dt>
-<dt>Mother-of-pearl, <a href="#Page_148">148</a></dt>
-<dt>Muscovite, <a href="#Page_129">129</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_N">N</dt>
-<dt>Natrolite, <a href="#Page_142">142</a></dt>
-<dt>Natural gas, <a href="#Page_227">227</a></dt>
-<dt>Needle iron stone, <a href="#Page_52">52</a></dt>
-<dt>Niccolite, <a href="#Page_83">83</a></dt>
-<dt>Nickel, copper, <a href="#Page_83">83</a></dt>
-<dt>Nickel group, <a href="#Page_82">82</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_O">O</dt>
-<dt>Obsidian, <a href="#Page_191">191</a></dt>
-<dt>Ochre red, <a href="#Page_54">54</a></dt>
-<dt>Ochre yellow, <a href="#Page_49">49</a></dt>
-<dt>Oligoclase, <a href="#Page_113">113</a>, <a href="#Page_115">115</a></dt>
-<dt>Olivine, <a href="#Page_134">134</a></dt>
-<dt>Olivine-gabbro, <a href="#Page_183">183</a></dt>
-<dt>Onyx, <a href="#Page_108">108</a></dt>
-<dt>Onyx, Californian, <a href="#Page_146">146</a></dt>
-<dt>Onyx marble, <a href="#Page_215">215</a></dt>
-<dt>Onyx, Mexican, <a href="#Page_146">146</a></dt>
-<dt>Oolites, <a href="#Page_254">254</a></dt>
-<dt>Opal, <a href="#Page_108">108</a></dt>
-<dt>Opal-agate, <a href="#Page_109">109</a></dt>
-<dt>Opal, common, <a href="#Page_109">109</a></dt>
-<dt>Opal, fire, <a href="#Page_109">109</a></dt>
-<dt>Opal, precious, <a href="#Page_109">109</a></dt>
-<dt>Ophicalcite, <a href="#Page_246">246</a></dt>
-<dt>Ophiolite, <a href="#Page_246">246</a></dt>
-<dt>Orpiment, <a href="#Page_80">80</a></dt>
-<dt>Orthoclase, <a href="#Page_110">110</a>, <a href="#Page_113">113</a></dt>
-<dt>Orthorhombic system, <a href="#Page_16">16</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_P">P</dt>
-<dt>Paste, <a href="#Page_103">103</a></dt>
-<dt>Pearls, <a href="#Page_148">148</a></dt>
-<dt>Pearlstone, <a href="#Page_193">193</a></dt>
-<dt>Peat, <a href="#Page_218">218</a>, <a href="#Page_219">219</a></dt>
-<dt>Pebbles, <a href="#Page_256">256</a></dt>
-<dt>Pegmatite, <a href="#Page_179">179</a></dt>
-<dt>Peridot, <a href="#Page_134">134</a></dt>
-<dt>Peridotite, <a href="#Page_184">184</a></dt>
-<dt>Perlite, <a href="#Page_193">193</a></dt>
-<dt>Petroleum series, <a href="#Page_224">224</a>, <a href="#Page_227">227</a></dt>
-<dt>Pewter, <a href="#Page_60">60</a></dt>
-<dt>Phenocrysts, <a href="#Page_189">189</a></dt>
-<dt>Phlogopite, <a href="#Page_129">129</a>, <a href="#Page_131">131</a></dt>
-<dt>Phosphate, <a href="#Page_160">160</a>, <a href="#Page_230">230</a></dt>
-<dt>Phosphorus, <a href="#Page_159">159</a></dt>
-<dt>Phyllite, <a href="#Page_242">242</a></dt>
-<dt>Picotite, <a href="#Page_97">97</a></dt>
-<dt>Pisolite, <a href="#Page_255">255</a></dt>
-<dt>Pitchstone, <a href="#Page_193">193</a></dt>
-<dt>Plagioclase, <a href="#Page_111">111</a></dt>
-<dt>Plasma, <a href="#Page_106">106</a></dt>
-<dt>Platinum, <a href="#Page_95">95</a></dt>
-<dt>Plumbago, <a href="#Page_156">156</a></dt>
-<dt>Porous, <a href="#Page_176">176</a></dt>
-<dt>Porphyritic, <a href="#Page_176">176</a></dt>
-<dt>Porphyry, <a href="#Page_189">189</a></dt>
-<dt>Prase, <a href="#Page_104">104</a></dt>
-<dt>Prousite, <a href="#Page_36">36</a></dt>
-<dt>Psilomelane, <a href="#Page_72">72</a></dt>
-<dt>Pumice, <a href="#Page_193">193</a></dt>
-<dt>Pyrargyrite, <a href="#Page_35">35</a></dt>
-<dt>Pyrite, <a href="#Page_56">56</a></dt>
-<dt>Pyrite, capillary, <a href="#Page_83">83</a></dt>
-<dt>Pyrite, magnetic, <a href="#Page_58">58</a></dt>
-<dt>Pyrite, white, <a href="#Page_57">57</a></dt>
-<dt>Pyritohedron, <a href="#Page_56">56</a>, <a href="#Page_318">318</a></dt>
-<dt>Pyrolusite, <a href="#Page_71">71</a></dt>
-<dt>Pyromorphite, <a href="#Page_63">63</a></dt>
-<dt>Pyrope, <a href="#Page_122">122</a>, <a href="#Page_123">123</a></dt>
-<dt>Pyroxene group, <a href="#Page_116">116</a></dt>
-<dt>Pyroxenite, <a href="#Page_185">185</a></dt>
-<dt>Pyrrhotite, <a href="#Page_58">58</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_Q">Q</dt>
-<dt>Quartz, <a href="#Page_100">100</a></dt>
-<dt>Quartz-diorite, <a href="#Page_181">181</a></dt>
-<dt>Quartz, milky, <a href="#Page_103">103</a></dt>
-<dt>Quartz, rose, <a href="#Page_104">104</a></dt>
-<dt>Quartz, smoky, <a href="#Page_103">103</a></dt>
-<dt>Quartzite, <a href="#Page_239">239</a></dt>
-<dt>Quicksands, <a href="#Page_204">204</a></dt>
-<dt>Quicksilver, <a href="#Page_90">90</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_R">R</dt>
-<dt>Radium, <a href="#Page_89">89</a></dt>
-<dt>Realgar, <a href="#Page_80">80</a></dt>
-<dt>Rhinestones, <a href="#Page_101">101</a></dt>
-<dt>Rhodochrosite, <a href="#Page_73">73</a></dt>
-<dt class="pb" id="Page_277">277</dt>
-<dt>Rhyolite 185</dt>
-<dt>Rock, phosphate, <a href="#Page_230">230</a></dt>
-<dt>Rocks, <a href="#Page_170">170</a></dt>
-<dt>Rocks, defined, <a href="#Page_10">10</a></dt>
-<dt>Rocks, igneous, <a href="#Page_172">172</a></dt>
-<dt>Rocks, igneous, classified, <a href="#Page_177">177</a></dt>
-<dt>Rocks, metamorphic, <a href="#Page_232">232</a></dt>
-<dt>Rocks, metamorphic, classified, <a href="#Page_236">236</a></dt>
-<dt>Rocks, sedimentary, <a href="#Page_194">194</a></dt>
-<dt>Rocks, sedimentary, classified, <a href="#Page_196">196</a></dt>
-<dt>Rubicelle, <a href="#Page_97">97</a></dt>
-<dt>Ruby, <a href="#Page_75">75</a></dt>
-<dt>Ruby, Balas, <a href="#Page_97">97</a></dt>
-<dt>Ruby mica, <a href="#Page_52">52</a></dt>
-<dt>Rutile, <a href="#Page_94">94</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_S">S</dt>
-<dt>Salt, <a href="#Page_163">163</a></dt>
-<dt>Sand, <a href="#Page_202">202</a></dt>
-<dt>Sandstone, <a href="#Page_205">205</a></dt>
-<dt>Sapphire, <a href="#Page_75">75</a></dt>
-<dt>Sapphire, Oriental white, <a href="#Page_75">75</a></dt>
-<dt>Sardonyx, <a href="#Page_108">108</a></dt>
-<dt>Satin spar, <a href="#Page_146">146</a></dt>
-<dt>Schist, <a href="#Page_240">240</a></dt>
-<dt>Schistosity, <a href="#Page_234">234</a></dt>
-<dt>Scoria, <a href="#Page_192">192</a>, <a href="#Page_193">193</a></dt>
-<dt>Septeria, <a href="#Page_252">252</a></dt>
-<dt>Sericite, <a href="#Page_130">130</a></dt>
-<dt>Serpentine, <a href="#Page_139">139</a>, <a href="#Page_245">245</a></dt>
-<dt>Shale, <a href="#Page_210">210</a></dt>
-<dt>Shale, oil-bearing, <a href="#Page_225">225</a></dt>
-<dt>Sheet, <a href="#Page_173">173</a></dt>
-<dt>Siderite, <a href="#Page_55">55</a></dt>
-<dt>Silica, <a href="#Page_99">99</a></dt>
-<dt>Silicates, <a href="#Page_99">99</a></dt>
-<dt>Silicon, <a href="#Page_99">99</a></dt>
-<dt>Sill, <a href="#Page_174">174</a></dt>
-<dt>Sillimanite, <a href="#Page_128">128</a></dt>
-<dt>Silver, <a href="#Page_34">34</a></dt>
-<dt>Silver, dark red, <a href="#Page_35">35</a></dt>
-<dt>Silver, German, <a href="#Page_65">65</a></dt>
-<dt>Silver glance, <a href="#Page_35">35</a></dt>
-<dt>Silver group, <a href="#Page_32">32</a></dt>
-<dt>Silver, horn, <a href="#Page_37">37</a></dt>
-<dt>Silver, light red, <a href="#Page_36">36</a></dt>
-<dt>Silver, ruby, <a href="#Page_35">35</a></dt>
-<dt>Sinter, <a href="#Page_110">110</a></dt>
-<dt>Slate, <a href="#Page_241">241</a></dt>
-<dt>Smalt, <a href="#Page_84">84</a></dt>
-<dt>Smaltite, <a href="#Page_85">85</a></dt>
-<dt>Smithsonite, <a href="#Page_68">68</a></dt>
-<dt>Soapstone, <a href="#Page_244">244</a></dt>
-<dt>Sodalite, <a href="#Page_126">126</a></dt>
-<dt>Soil, <a href="#Page_198">198</a></dt>
-<dt>Solder, <a href="#Page_60">60</a></dt>
-<dt>Specific gravity, <a href="#Page_22">22</a></dt>
-<dt>Speigeleisen, <a href="#Page_70">70</a></dt>
-<dt>Spelter, <a href="#Page_64">64</a></dt>
-<dt>Spessartite, <a href="#Page_122">122</a>, <a href="#Page_123">123</a></dt>
-<dt>Sphalerite, <a href="#Page_65">65</a></dt>
-<dt>Spinel, <a href="#Page_97">97</a></dt>
-<dt>Spinel-ruby, <a href="#Page_97">97</a></dt>
-<dt>Stalactites, <a href="#Page_146">146</a></dt>
-<dt>Stalagmites, <a href="#Page_146">146</a></dt>
-<dt>Staurolite, <a href="#Page_133">133</a></dt>
-<dt>Steatite, <a href="#Page_244">244</a></dt>
-<dt>Stellite, <a href="#Page_84">84</a>, <a href="#Page_88">88</a></dt>
-<dt>Stibnite, <a href="#Page_81">81</a></dt>
-<dt>Stilbite, <a href="#Page_143">143</a></dt>
-<dt>Stock, <a href="#Page_174">174</a></dt>
-<dt>Streak, <a href="#Page_23">23</a></dt>
-<dt>Strontianite, <a href="#Page_152">152</a></dt>
-<dt>Strontium group, <a href="#Page_152">152</a></dt>
-<dt>Sulphur, <a href="#Page_166">166</a></dt>
-<dt>Syenite, <a href="#Page_180">180</a></dt>
-<dt>Sylvanite, <a href="#Page_30">30</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_T">T</dt>
-<dt>Talc, <a href="#Page_138">138</a></dt>
-<dt>Talus, <a href="#Page_197">197</a></dt>
-<dt>Tetragonal system, <a href="#Page_15">15</a></dt>
-<dt>Tetrahedrite, <a href="#Page_43">43</a></dt>
-<dt>Tile ore, <a href="#Page_45">45</a></dt>
-<dt>Till, <a href="#Page_215">215</a></dt>
-<dt>Tillite, <a href="#Page_217">217</a></dt>
-<dt>Time chart, <a href="#Page_268">268</a></dt>
-<dt>Tin, <a href="#Page_92">92</a></dt>
-<dt>Tin stone, <a href="#Page_93">93</a></dt>
-<dt>Titanium, <a href="#Page_93">93</a></dt>
-<dt>Tonalite, <a href="#Page_181">181</a></dt>
-<dt>Topaz, <a href="#Page_131">131</a></dt>
-<dt>Topaz, false, <a href="#Page_103">103</a></dt>
-<dt>Topaz, Oriental, <a href="#Page_75">75</a></dt>
-<dt>Topaz, Saxon, <a href="#Page_132">132</a></dt>
-<dt>Topaz, Scotch, <a href="#Page_132">132</a></dt>
-<dt>Topaz, smoky, <a href="#Page_132">132</a></dt>
-<dt>Topaz, Spanish, <a href="#Page_132">132</a></dt>
-<dt>Tourmaline, <a href="#Page_135">135</a></dt>
-<dt>Trachite, <a href="#Page_186">186</a></dt>
-<dt>Trap, <a href="#Page_188">188</a></dt>
-<dt>Travertine, <a href="#Page_146">146</a>, <a href="#Page_215">215</a></dt>
-<dt class="pb" id="Page_278">278</dt>
-<dt>Tremolite, <a href="#Page_120">120</a></dt>
-<dt>Triclinic system, <a href="#Page_18">18</a></dt>
-<dt>Tripolite, <a href="#Page_110">110</a></dt>
-<dt>Tufa, calcareous, <a href="#Page_147">147</a></dt>
-<dt>Tuff, <a href="#Page_190">190</a></dt>
-<dt>Tungsten, <a href="#Page_87">87</a></dt>
-<dt>Turgite, <a href="#Page_51">51</a></dt>
-<dt>Turquois, <a href="#Page_161">161</a></dt>
-<dt>Twinning, <a href="#Page_19">19</a></dt>
-<dt>Type metal, <a href="#Page_60">60</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_U">U</dt>
-<dt>Uintaite, <a href="#Page_229">229</a></dt>
-<dt>Uranium, <a href="#Page_89">89</a></dt>
-<dt>Uvarovite, <a href="#Page_122">122</a>, <a href="#Page_123">123</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_V">V</dt>
-<dt>Vanadium, <a href="#Page_89">89</a></dt>
-<dt>Verde antique, <a href="#Page_247">247</a></dt>
-<dt>Volcanic ash, <a href="#Page_190">190</a></dt>
-<dt>Volcanic blocks, <a href="#Page_191">191</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_W">W</dt>
-<dt>Water, <a href="#Page_167">167</a></dt>
-<dt>White metal, <a href="#Page_64">64</a></dt>
-<dt>Willemite, <a href="#Page_67">67</a></dt>
-<dt>Witherite, <a href="#Page_153">153</a></dt>
-<dt>Wolframite, <a href="#Page_88">88</a></dt>
-<dt>Wood, agatized, <a href="#Page_108">108</a></dt>
-<dt>Wood, opalized, <a href="#Page_109">109</a></dt>
-<dt>Wood, silicified, <a href="#Page_108">108</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_X">X</dt>
-<dt>Xanthosiderite, <a href="#Page_51">51</a></dt>
-</dl>
-<dl class="index">
-<dt class="center b" id="index_Z">Z</dt>
-<dt>Zeolites, <a href="#Page_141">141</a></dt>
-<dt>Zinc, <a href="#Page_63">63</a></dt>
-<dt>Zinc blende, <a href="#Page_65">65</a></dt>
-<dt>Zinc red ore, <a href="#Page_66">66</a></dt>
-<dt>Zinc, ruby, <a href="#Page_65">65</a></dt>
-<dt>Zincite, <a href="#Page_66">66</a></dt>
-<dt>Zircon, <a href="#Page_127">127</a></dt>
-</dl>
-<div class="pb" id="Page_279">279</div>
-<h3 class="plate" id="Plate_Frontispiece">Plate Frontispiece</h3>
-<div class="img" id="fig1">
-<img src="images/p01.jpg" alt="" width="539" height="901" />
-<p class="pcap">Tourmaline crystals, growing amid feldspar crystals in a
-cavity in granite, from Paris, Me.</p>
-</div>
-<div class="pb" id="Page_280">280</div>
-<h3 class="plate" id="Plate_5">Plate 5</h3>
-<div class="img" id="fig2">
-<img src="images/p02.jpg" alt="" width="600" height="518" />
-<p class="pcap">Gold in quartz, from California</p>
-</div>
-<div class="pb" id="Page_281">281</div>
-<h3 class="plate" id="Plate_6">Plate 6</h3>
-<div class="img" id="fig3">
-<img src="images/p02a.jpg" alt="" width="600" height="475" />
-<p class="pcap">Native silver in calcite</p>
-</div>
-<div class="img" id="fig4">
-<img src="images/p02b.jpg" alt="" width="600" height="467" />
-<p class="pcap">Argentite, the black masses throughout the white quartz</p>
-</div>
-<div class="pb" id="Page_282">282</div>
-<h3 class="plate" id="Plate_7">Plate 7</h3>
-<div class="img" id="fig5">
-<img src="images/p03.jpg" alt="" width="600" height="577" />
-<p class="pcap">Pyrargyrite as it appears after moderate exposure
-to the light.</p>
-</div>
-<div class="img" id="fig6">
-<img src="images/p03a.jpg" alt="" width="300" height="425" />
-<p class="pcap">Crystal form of Pyrargyrite</p>
-</div>
-<div class="img" id="fig7">
-<img src="images/p03b.jpg" alt="" width="500" height="511" />
-<p class="pcap">Prousite as it appears after moderate exposure to the light</p>
-</div>
-<div class="pb" id="Page_283">283</div>
-<h3 class="plate" id="Plate_8">Plate 8</h3>
-<div class="img" id="fig8">
-<img src="images/p03d.jpg" alt="" width="600" height="463" />
-<p class="pcap">Native copper from Michigan</p>
-</div>
-<div class="img" id="fig9">
-<img src="images/p03e.jpg" alt="" width="600" height="468" />
-<p class="pcap">Chalcopyrite in tetrahedrons and an occasional octahedron.</p>
-</div>
-<div class="pb" id="Page_284">284</div>
-<h3 class="plate" id="Plate_9">Plate 9</h3>
-<div class="img" id="fig10">
-<img src="images/p04.jpg" alt="" width="600" height="555" />
-<p class="pcap">Chalcocite crystals with the bluish tarnish</p>
-</div>
-<div class="img" id="fig11">
-<img src="images/p04a.jpg" alt="" width="600" height="506" />
-<p class="pcap">Tetrahedrite crystals</p>
-</div>
-<div class="pb" id="Page_285">285</div>
-<h3 class="plate" id="Plate_11">Plate 11</h3>
-<div class="img" id="fig12">
-<img src="images/p04c.jpg" alt="" width="600" height="520" />
-<p class="pcap">Cuprite, the red crystals showing characteristic color,
-other showing the green tarnish of malachite</p>
-</div>
-<div class="img" id="fig13">
-<img src="images/p04d.jpg" alt="" width="600" height="468" />
-<p class="pcap">Malachite (green) and azurite (blue), the two minerals
-shown together as they very commonly occur</p>
-</div>
-<div class="pb" id="Page_286">286</div>
-<h3 class="plate" id="Plate_12">Plate 12</h3>
-<div class="img" id="fig14">
-<img src="images/p05.jpg" alt="" width="600" height="386" />
-<p class="pcap">Limonite</p>
-</div>
-<div class="img" id="fig15">
-<img src="images/p05a.jpg" alt="" width="300" height="495" />
-<p class="pcap">The crystal form in which goethite is found,
-<i>p</i> is the prism faces, <i>b</i> and <i>c</i> are
-faces formed by beveling the edges of the prism, <i>o</i> is
-the pyramidal face characteristic of the ends</p>
-</div>
-<div class="pb" id="Page_287">287</div>
-<h3 class="plate" id="Plate_13">Plate 13</h3>
-<div class="img" id="fig16">
-<img src="images/p05c.jpg" alt="" width="600" height="404" />
-<p class="pcap">Hematite, Clinton iron ore, oolitic</p>
-</div>
-<div class="img" id="fig17">
-<img src="images/p05d.jpg" alt="" width="600" height="514" />
-<p class="pcap">Siderite crystals</p>
-</div>
-<div class="pb" id="Page_288">288</div>
-<h3 class="plate" id="Plate_15">Plate 15</h3>
-<div class="img" id="fig18">
-<img src="images/p06.jpg" alt="" width="600" height="494" />
-<p class="pcap">Pyrite crystals</p>
-</div>
-<div class="img" id="fig19">
-<img src="images/p06a.jpg" alt="" width="600" height="586" />
-<p class="pcap">Marcasite in concretionary form with radiate structure</p>
-</div>
-<div class="pb" id="Page_289">289</div>
-<h3 class="plate" id="Plate_17">Plate 17</h3>
-<div class="img" id="fig20">
-<img src="images/p06c.jpg" alt="" width="600" height="437" />
-<p class="pcap">Galena in crystals</p>
-</div>
-<div class="img" id="fig21">
-<img src="images/p06d.jpg" alt="" width="600" height="566" />
-<p class="pcap">Pyromorphite crystals (green)</p>
-</div>
-<div class="pb" id="Page_290">290</div>
-<h3 class="plate" id="Plate_19">Plate 19</h3>
-<div class="img" id="fig22">
-<img src="images/p07.jpg" alt="" width="600" height="430" />
-<p class="pcap">Sphalerite, some the normal yellow and some crystals with
-the reddish tinge. (White is dolomite)</p>
-</div>
-<div class="img" id="fig23">
-<img src="images/p07a.jpg" alt="" width="600" height="473" />
-<p class="pcap">Zincite</p>
-</div>
-<div class="pb" id="Page_291">291</div>
-<h3 class="plate" id="Plate_21">Plate 21</h3>
-<div class="img" id="fig24">
-<img src="images/p07c.jpg" alt="" width="600" height="476" />
-<p class="pcap">Smithsonite in yellow crystals</p>
-</div>
-<div class="img" id="fig25">
-<img src="images/p07d.jpg" alt="" width="600" height="478" />
-<p class="pcap">Franklinite in octahedral crystals</p>
-</div>
-<div class="pb" id="Page_292">292</div>
-<h3 class="plate" id="Plate_24">Plate 24</h3>
-<div class="img" id="fig26">
-<img src="images/p08.jpg" alt="" width="600" height="497" />
-<p class="pcap">Arsenopyrite, showing crystals massed so as to be incompletely
-developed</p>
-</div>
-<div class="img" id="fig27">
-<img src="images/p08a.jpg" alt="" width="600" height="473" />
-<p class="pcap">Realgar as it usually occurs in powdery incrustations</p>
-</div>
-<div class="pb" id="Page_293">293</div>
-<h3 class="plate" id="Plate_25">Plate 25</h3>
-<div class="img" id="fig28">
-<img src="images/p08c.jpg" alt="" width="600" height="218" />
-<p class="pcap">Large crystal of stibnite, the light colored face is the one
-parallel to which cleavage occurs</p>
-</div>
-<div class="img" id="fig29">
-<img src="images/p08d.jpg" alt="" width="600" height="489" />
-<p class="pcap">Niccolite as a vein in slate</p>
-</div>
-<div class="pb" id="Page_294">294</div>
-<h3 class="plate" id="Plate_26">Plate 26</h3>
-<div class="img" id="fig30">
-<img src="images/p09.jpg" alt="" width="600" height="539" />
-<p class="pcap">Cobaltite, silver color, with pink tinge</p>
-</div>
-<div class="img" id="fig31">
-<img src="images/p09a.jpg" alt="" width="600" height="408" />
-<p class="pcap">Smaltite, pink is cobalt bloom</p>
-</div>
-<div class="pb" id="Page_295">295</div>
-<h3 class="plate" id="Plate_27">Plate 27</h3>
-<div class="img" id="fig32">
-<img src="images/p09d.jpg" alt="" width="600" height="322" />
-<p class="pcap">Carnotite from southwest Colorado</p>
-</div>
-<div class="img" id="fig33">
-<img src="images/p09e.jpg" alt="" width="600" height="577" />
-<p class="pcap">Cinnabar</p>
-</div>
-<div class="pb" id="Page_296">296</div>
-<h3 class="plate" id="Plate_31">Plate 31</h3>
-<div class="img" id="fig34">
-<img src="images/p10.jpg" alt="" width="600" height="503" />
-<p class="pcap">Amethyst, not however deep enough colored for gems</p>
-</div>
-<div class="img" id="fig35">
-<img src="images/p10a.jpg" alt="" width="424" height="600" />
-<p class="pcap">Jasper, with botryoidal surface</p>
-</div>
-<div class="pb" id="Page_297">297</div>
-<h3 class="plate" id="Plate_32">Plate 32</h3>
-<div class="img" id="fig36">
-<img src="images/p10b.jpg" alt="" width="600" height="755" />
-<p class="pcap">Banded Agate from Brazil</p>
-</div>
-<div class="pb" id="Page_298">298</div>
-<h3 class="plate" id="Plate_33">Plate 33</h3>
-<div class="img" id="fig37">
-<img src="images/p11.jpg" alt="" width="600" height="441" />
-<p class="pcap">Common Opal from Arizona</p>
-</div>
-<div class="img" id="fig38">
-<img src="images/p11a.jpg" alt="" width="600" height="485" />
-<p class="pcap">Siliceous sinter or Geyserite from The Yellowstone Park</p>
-</div>
-<div class="pb" id="Page_299">299</div>
-<h3 class="plate" id="Plate_35">Plate 35</h3>
-<div class="img" id="fig39">
-<img src="images/p11b.jpg" alt="" width="600" height="439" />
-<p class="pcap">A group of Microcline crystals from Pike&rsquo;s Peak, Colo.</p>
-</div>
-<div class="img" id="fig40">
-<img src="images/p11d.jpg" alt="" width="600" height="395" />
-<p class="pcap">Labradorite, showing multiple twinning (the striation),
-and the iridescent play of colors</p>
-</div>
-<div class="pb" id="Page_300">300</div>
-<h3 class="plate" id="Plate_36">Plate 36</h3>
-<div class="img" id="fig41">
-<img src="images/p12.jpg" alt="" width="289" height="356" />
-<p class="pcap">Crystal form of a pyroxene; <i>a</i>
-and <i>b</i> prism faces, <i>m</i> the beveled
-edge between two prism faces</p>
-</div>
-<div class="img" id="fig42">
-<img src="images/p12a.jpg" alt="" width="312" height="313" />
-<p class="pcap">Cross section of a pyroxene crystal showing the lines of intersection
-of the two cleavage planes</p>
-</div>
-<div class="img" id="fig43">
-<img src="images/p12b.jpg" alt="" width="600" height="209" />
-<p class="pcap">Cross sections of pyroxenes, showing typical forms taken by crystals</p>
-</div>
-<div class="img" id="fig44">
-<img src="images/p12g.jpg" alt="" width="600" height="507" />
-<p class="pcap">Augite crystals, in crystalline limestone</p>
-</div>
-<div class="pb" id="Page_301">301</div>
-<h3 class="plate" id="Plate_38">Plate 38</h3>
-<div class="img" id="fig45">
-<img src="images/p12h.jpg" alt="" width="659" height="318" />
-<p class="pcap">The dodecahedron and the 24-sided figure characteristic of garnets</p>
-</div>
-<div class="img" id="fig46">
-<img src="images/p12i.jpg" alt="" width="600" height="524" />
-<p class="pcap">The garnet, grossularite</p>
-</div>
-<div class="img" id="fig47">
-<img src="images/p12j.jpg" alt="" width="600" height="338" />
-<p class="pcap">The garnet alamandite</p>
-</div>
-<div class="pb" id="Page_302">302</div>
-<h3 class="plate" id="Plate_39">Plate 39</h3>
-<div class="img" id="fig48">
-<img src="images/p13.jpg" alt="" width="489" height="600" />
-<p class="pcap">Beryl of gem quality</p>
-</div>
-<div class="img" id="fig49">
-<img src="images/p13a.jpg" alt="" width="600" height="479" />
-<p class="pcap">Zircon in syenite</p>
-</div>
-<div class="pb" id="Page_303">303</div>
-<h3 class="plate" id="Plate_40">Plate 40</h3>
-<div class="img" id="fig50">
-<img src="images/p13c.jpg" alt="" width="600" height="306" />
-<p class="pcap">Cyanite crystals in schist</p>
-</div>
-<div class="img" id="fig51">
-<img src="images/p13d.jpg" alt="" width="600" height="524" />
-<p class="pcap">A crystal of mica, showing basal cleavage</p>
-</div>
-<div class="pb" id="Page_304">304</div>
-<h3 class="plate" id="Plate_41">Plate 41</h3>
-<div class="img" id="fig52">
-<img src="images/p14.jpg" alt="" width="300" height="547" />
-<p class="pcap">Crystal form typical of topaz</p>
-</div>
-<div class="img" id="fig53">
-<img src="images/p14a.jpg" alt="" width="439" height="600" />
-<p class="pcap">A topaz crystal from Brazil</p>
-</div>
-<div class="img" id="fig54">
-<img src="images/p14b.jpg" alt="" width="157" height="300" />
-<p class="pcap">Crystal form typical of staurolite when simple</p>
-</div>
-<div class="img" id="fig55">
-<img src="images/p14d.jpg" alt="" width="500" height="501" />
-<p class="pcap">A typical twin of staurolite</p>
-</div>
-<div class="pb" id="Page_305">305</div>
-<h3 class="plate" id="Plate_43">Plate 43</h3>
-<div class="img" id="fig56">
-<img src="images/p14e.jpg" alt="" width="600" height="450" />
-<p class="pcap">Serpentine</p>
-</div>
-<div class="img" id="fig57">
-<img src="images/p14f.jpg" alt="" width="600" height="316" />
-<p class="pcap">Chlorite</p>
-</div>
-<div class="pb" id="Page_306">306</div>
-<h3 class="plate" id="Plate_49">Plate 49</h3>
-<div class="img" id="fig58">
-<img src="images/p15.jpg" alt="" width="600" height="413" />
-<p class="pcap">Apatite crystals in crystalline calcite</p>
-</div>
-<div class="img" id="fig59">
-<img src="images/p15a.jpg" alt="" width="500" height="325" />
-<p class="pcap">The ends of apatite crystals showing common modes of termination</p>
-</div>
-<div class="pb" id="Page_307">307</div>
-<h3 class="plate" id="Plate_50">Plate 50</h3>
-<div class="img" id="fig60">
-<img src="images/p15b.jpg" alt="" width="600" height="500" />
-<p class="pcap">A group of fluorite crystals</p>
-</div>
-<div class="img" id="fig61">
-<img src="images/p15d.jpg" alt="" width="600" height="415" />
-<p class="pcap">A group of halite crystals</p>
-</div>
-<div class="pb" id="Page_308">308</div>
-<h3 class="plate" id="Plate_61">Plate 61</h3>
-<div class="img" id="fig62">
-<img src="images/p16.jpg" alt="" width="600" height="340" />
-<p class="pcap">Amber</p>
-</div>
-<div class="img" id="fig63">
-<img src="images/p16a.jpg" alt="" width="600" height="751" />
-<p class="pcap">Two bottles of petroleum, the left hand one with a paraffin
-base, the right hand one with an asphalt base</p>
-</div>
-<div class="pb" id="Page_309">309</div>
-<h3 class="plate" id="Plate_65">Plate 65</h3>
-<div class="img" id="fig64">
-<img src="images/p16c.jpg" alt="" width="600" height="451" />
-<p class="pcap">Mica schist, with garnets</p>
-</div>
-<div class="img" id="fig65">
-<img src="images/p16d.jpg" alt="" width="600" height="473" />
-<p class="pcap">Chlorite schist</p>
-</div>
-<div class="pb" id="Page_310">310</div>
-<h3 class="plate" id="Plate_67">Plate 67</h3>
-<div class="img" id="fig66">
-<img src="images/p17.jpg" alt="" width="563" height="800" />
-<p class="pcap">Serpentine, composed of serpentine, hematite, and some calcite</p>
-</div>
-<div class="pb" id="Page_311">311</div>
-<h3 class="plate" id="Plate_1">Plate 1</h3>
-<h4 class="plate">Basal forms of the isometric system</h4>
-<div class="img" id="fig67">
-<img src="images/p17a.jpg" alt="" width="500" height="415" />
-<p class="pcap">Cube</p>
-</div>
-<div class="img" id="fig68">
-<img src="images/p17c.jpg" alt="" width="498" height="655" />
-<p class="pcap">Octahedron</p>
-</div>
-<div class="img" id="fig69">
-<img src="images/p17d.jpg" alt="" width="500" height="500" />
-<p class="pcap">Dodecahedron</p>
-</div>
-<div class="pb" id="Page_312">312</div>
-<h3 class="plate" id="Plate_2">Plate 2</h3>
-<h4 class="plate">Basal forms of the tetragonal system</h4>
-<div class="img" id="fig70">
-<img src="images/p18.jpg" alt="" width="324" height="382" />
-<p class="pcap">A square prism</p>
-</div>
-<div class="img" id="fig71">
-<img src="images/p18c.jpg" alt="" width="347" height="350" />
-<p class="pcap">Octahedron</p>
-</div>
-<h4 class="plate">Basal forms of the orthorhombic system</h4>
-<div class="img" id="fig72">
-<img src="images/p18d.jpg" alt="" width="373" height="409" />
-<p class="pcap">A Rectangular prism</p>
-</div>
-<div class="img" id="fig73">
-<img src="images/p18e.jpg" alt="" width="278" height="376" />
-<p class="pcap">Octahedron</p>
-</div>
-<div class="pb" id="Page_313">313</div>
-<h3 class="plate" id="Plate_3">Plate 3</h3>
-<h4 class="plate">Basal forms of the monoclinic system</h4>
-<div class="img" id="fig74">
-<img src="images/p18f.jpg" alt="" width="262" height="532" />
-<p class="pcap">The rectangular prism askew</p>
-</div>
-<div class="img" id="fig75">
-<img src="images/p18g.jpg" alt="" width="141" height="340" />
-<p class="pcap">The octahedron</p>
-</div>
-<div class="img" id="fig76">
-<img src="images/p18h.jpg" alt="" width="345" height="207" />
-<p class="pcap">A cross section of the prism with its edges beveled so that
-the <i>b</i> faces are obliterated by the <i>m</i> faces, and a six-sided prism
-is formed (pseudo-hexagonal)</p>
-</div>
-<div class="img" id="fig77">
-<img src="images/p18i.jpg" alt="" width="376" height="551" />
-<p class="pcap">Basal form of the triclinic system</p>
-</div>
-<div class="pb" id="Page_314">314</div>
-<h3 class="plate" id="Plate_4">Plate 4</h3>
-<h4 class="plate">Basal forms of the hexagonal system</h4>
-<div class="img" id="fig78">
-<img src="images/p19.jpg" alt="" width="260" height="582" />
-<p class="pcap">The six-sided prism</p>
-</div>
-<div class="img" id="fig79">
-<img src="images/p19a.jpg" alt="" width="297" height="527" />
-<p class="pcap">The double pyramid</p>
-</div>
-<div class="img" id="fig80">
-<img src="images/p19d.jpg" alt="" width="334" height="340" />
-<p class="pcap">The rhombohedron</p>
-</div>
-<div class="pb" id="Page_315">315</div>
-<h3 class="plate" id="Plate_10">Plate 10</h3>
-<div class="img" id="fig81">
-<img src="images/p19f.jpg" alt="" width="532" height="222" />
-<p class="pcap">Tetrahedrons showing characteristic manner in which
-tetrahedrite occurs</p>
-</div>
-<div class="img" id="fig82">
-<img src="images/p19g.jpg" alt="" width="464" height="413" />
-<p class="pcap">A cube with the edges beveled and
-the corners cut in a form characteristic of cuprite</p>
-</div>
-<div class="pb" id="Page_316">316</div>
-<h3 class="plate" id="Plate_30">Plate 30</h3>
-<div class="img" id="fig83">
-<img src="images/p20.jpg" alt="" width="600" height="601" />
-<p class="pcap">Two intergrowing or twinned quartz crystals</p>
-</div>
-<div class="img" id="fig84">
-<img src="images/p20b.jpg" alt="" width="300" height="547" />
-<p class="pcap">Diagram of the typical quartz crystal, <i>p</i> prism faces,
-<i>l</i> left hand rhombohedron, <i>r</i> right hand rhombohedron</p>
-</div>
-<div class="img" id="fig85">
-<img src="images/p20c.jpg" alt="" width="300" height="516" />
-<p class="pcap">A quartz crystal on which the left hand rhombohedron
-is represented by small faces while the right hand rhombohedron has large faces</p>
-</div>
-<div class="pb" id="Page_317">317</div>
-<h3 class="plate" id="Plate_14">Plate 14</h3>
-<div class="img" id="fig86">
-<img src="images/p20d.jpg" alt="" width="500" height="284" />
-<p class="pcap">Crystal forms of hematite, <i>A</i> the rhombohedron with
-the edges beveled; <i>B</i> the tabular form, resulting from the
-excessive development of the two <i>o</i> faces opposite each
-other</p>
-</div>
-<div class="img" id="fig87">
-<img src="images/p20e.jpg" alt="" width="400" height="382" />
-<p class="pcap">A typical crystal of magnetite</p>
-</div>
-<div class="img" id="fig88">
-<img src="images/p20f.jpg" alt="" width="300" height="325" />
-<p class="pcap">The rhombohedron typical of siderite</p>
-</div>
-<div class="pb" id="Page_318">318</div>
-<h3 class="plate" id="Plate_16">Plate 16</h3>
-<div class="img" id="fig89">
-<img src="images/p21.jpg" alt="" width="542" height="498" />
-<p class="pcap">The pyritohedron</p>
-</div>
-<div class="img" id="fig90">
-<img src="images/p21d.jpg" alt="" width="534" height="465" />
-<p class="pcap">The pyritohedron with certain of its edges beveled by the cube faces, to
-show the relationship of these two forms</p>
-</div>
-<div class="pb" id="Page_319">319</div>
-<h3 class="plate" id="Plate_18">Plate 18</h3>
-<h4 class="plate">Typical forms for cerrusite</h4>
-<div class="img" id="fig91">
-<img src="images/p21e.jpg" alt="" width="293" height="417" />
-<p class="pcap">The pyramid, <i>n</i> the
-prism face, <i>m</i> the beveled prism, <i>p</i> the octahedral
-face, and <i>o</i> the edge of the octahedral faces beveled</p>
-</div>
-<div class="img" id="fig92">
-<img src="images/p21f.jpg" alt="" width="219" height="332" />
-<p class="pcap">The simple type of twinning</p>
-</div>
-<div class="img" id="fig93">
-<img src="images/p21g.jpg" alt="" width="374" height="424" />
-<p class="pcap">A multiple twin where three crystals grow through each other</p>
-</div>
-<div class="img" id="fig94">
-<img src="images/p21i.jpg" alt="" width="500" height="531" />
-<p class="pcap">Forms in which anglesite occurs: <i>l</i> the pyramid face, <i>p</i>
-the prism face, <i>o</i> the vertical edge of the prism beveled,
-<i>m</i> the horizontal edge of the prism beveled, <i>n</i> a further
-beveling of the horizontal edge of the prism. <i>D</i> the
-tabular, <i>E</i> the prismatic form</p>
-</div>
-<div class="pb" id="Page_320">320</div>
-<h3 class="plate" id="Plate_20">Plate 20</h3>
-<div class="img" id="fig95">
-<img src="images/p22.jpg" alt="" width="515" height="519" />
-<p class="pcap">A characteristic form in which sphalerite
-may occur; being the combination of, <i>d</i> the
-dodecahedron, <i>o</i> the octahedron, and <i>t</i>, a 24-sided figure</p>
-</div>
-<div class="img" id="fig96">
-<img src="images/p22b.jpg" alt="" width="351" height="393" />
-<p class="pcap">Characteristic form for zincite
-crystals, <i>n</i> the hexagonal
-prism, and <i>p</i> pyramidal faces on it</p>
-</div>
-<div class="img" id="fig97">
-<img src="images/p22d.jpg" alt="" width="221" height="437" />
-<p class="pcap">Typical form of crystal of willemite:
-<i>p</i> the prism, <i>r</i> rhombohedron faces on
-end, &frac12; <i>r</i> a second lower rhombohedron</p>
-</div>
-<div class="pb" id="Page_321">321</div>
-<h3 class="plate" id="Plate_22">Plate 22</h3>
-<div class="img" id="fig98">
-<img src="images/p22f.jpg" alt="" width="600" height="569" />
-<p class="pcap">Moss agates, showing the dendritic growth
-of manganitic minerals, like manganite or pyrolusite</p>
-</div>
-<div class="img">
-<img src="images/p22g.jpg" alt="Moss agates" width="600" height="321" />
-</div>
-<div class="img" id="fig99">
-<img src="images/p22n.jpg" alt="" width="247" height="400" />
-<p class="pcap">Crystal form of manganite</p>
-</div>
-<div class="pb" id="Page_322">322</div>
-<h3 class="plate" id="Plate_23">Plate 23</h3>
-<div class="img" id="fig100">
-<img src="images/p23.jpg" alt="" width="600" height="439" />
-<p class="pcap">Crystals of green corundum in syenite, from Montana</p>
-</div>
-<div class="img" id="fig101">
-<img src="images/p23a.jpg" alt="" width="479" height="601" />
-<p class="pcap">Typical crystal forms of corundum: <i>A</i> the elongated
-prism with the alternate corners cut by
-rhombohedral faces, <i>B</i> the tabular prism, <i>C</i> the
-double pyramid</p>
-</div>
-<div class="pb" id="Page_323">323</div>
-<h3 class="plate" id="Plate_28">Plate 28</h3>
-<div class="img" id="fig102">
-<img src="images/p23e.jpg" alt="" width="600" height="694" />
-<p class="pcap">Cassiterite, twinned crystals</p>
-</div>
-<div class="img" id="fig103">
-<img src="images/p23f.jpg" alt="" width="274" height="395" />
-<p class="pcap">The crystal form in which both
-cassiterite and rutile occur when in
-simple crystals, <i>p</i> prism faces, <i>m</i>
-beveling of the prism, <i>o</i> octahedral
-face, <i>n</i> beveling of the edge between
-octahedral faces</p>
-</div>
-<div class="img" id="fig104">
-<img src="images/p23g.jpg" alt="" width="255" height="380" />
-<p class="pcap">Multiple twinning characteristic of rutile</p>
-</div>
-<div class="pb" id="Page_324">324</div>
-<h3 class="plate" id="Plate_29">Plate 29</h3>
-<div class="img" id="fig105">
-<img src="images/p24a1.jpg" alt="" width="600" height="474" />
-<p class="pcap">Crystal of Spinel</p>
-</div>
-<h4 class="plate">Crystal forms in which dolomite occurs</h4>
-<div class="img" id="fig106">
-<img src="images/p24a2.jpg" alt="" width="365" height="296" />
-<p class="pcap"><i>A</i> the cleavage form, rhombohedron with the faces curved</p>
-</div>
-<div class="img" id="fig107">
-<img src="images/p24a4.jpg" alt="" width="338" height="256" />
-<p class="pcap"><i>B</i> the rhombohedron with the corners cut, as it often occurs</p>
-</div>
-<div class="img" id="fig108">
-<img src="images/p24a5.jpg" alt="" width="158" height="268" />
-<p class="pcap"><i>C</i> the form found in gypsum or anhydrite</p>
-</div>
-<div class="pb" id="Page_325">325</div>
-<h3 class="plate" id="Plate_34">Plate 34</h3>
-<div class="img" id="fig109">
-<img src="images/p24b1.jpg" alt="" width="600" height="485" />
-<p class="pcap">Orthoclase, a cleavage piece, <i>a</i> and <i>b</i> the perfect
-cleavage planes, and <i>c</i> the imperfect cleavage plane</p>
-</div>
-<h4 class="plate">Crystal forms of orthoclase</h4>
-<div class="img" id="fig110">
-<img src="images/p24b2.jpg" alt="" width="169" height="283" />
-<p class="pcap"><i>A</i> the simple crystal</p>
-</div>
-<div class="img" id="fig111">
-<img src="images/p24b4.jpg" alt="" width="170" height="284" />
-<p class="pcap"><i>B</i> the twinned form</p>
-</div>
-<div class="img" id="fig112">
-<img src="images/p24b5.jpg" alt="" width="167" height="282" />
-<p class="pcap"><i>C</i> the twinned form in which the crystals are intergrowing</p>
-</div>
-<div class="img" id="fig113">
-<img src="images/p24b6.jpg" alt="" width="356" height="428" />
-<p class="pcap">Diagram of a multiple twin of a plagioclase feldspar</p>
-</div>
-<div class="pb" id="Page_326">326</div>
-<h3 class="plate" id="Plate_37">Plate 37</h3>
-<h4 class="plate">Diagrams of amphibole crystals</h4>
-<div class="img" id="fig114">
-<img src="images/p25.jpg" alt="" width="194" height="501" />
-<p class="pcap"><i>A</i> a typical crystal</p>
-</div>
-<div class="img" id="fig115">
-<img src="images/p25a.jpg" alt="" width="295" height="454" />
-<p class="pcap"><i>B</i> cross section showing the intersection of cleavage planes</p>
-</div>
-<div class="img" id="fig116">
-<img src="images/p25a2.jpg" alt="" width="360" height="297" />
-<p class="pcap"><i>C</i> and <i>D</i> cross sections to show variations in outline</p>
-</div>
-<div class="img" id="fig117">
-<img src="images/p25b1.jpg" alt="" width="600" height="335" />
-<p class="pcap">Tremolite in silky
-fibrous crystals. Asbestos</p>
-</div>
-<div class="img" id="fig118">
-<img src="images/p25b2.jpg" alt="" width="600" height="530" />
-<p class="pcap">Hornblende crystals in quartzite</p>
-</div>
-<div class="pb" id="Page_327">327</div>
-<h3 class="plate" id="Plate_42">Plate 42</h3>
-<div class="img" id="fig119">
-<img src="images/p25b3.jpg" alt="" width="600" height="368" />
-<p class="pcap">Epidote crystals</p>
-</div>
-<div class="img" id="fig120">
-<img src="images/p25c3.jpg" alt="" width="406" height="372" />
-<p class="pcap">Typical forms of epidote crystals;
-<i>p</i> prism faces, <i>m</i>, <i>n</i>, <i>x</i>, and
-<i>y</i> beveled edges of the prism,
-<i>o</i> octahedral faces</p>
-</div>
-<h4 class="plate">Typical forms of tourmaline</h4>
-<div class="img" id="fig121">
-<img src="images/p25c4.jpg" alt="" width="600" height="642" />
-<p class="pcap"><i>A</i> side view; <i>B</i>
-and <i>C</i> ends to show terminations;
-<i>p</i> prism faces,
-<i>m</i> beveling of prism
-edges, <i>r</i> a low rhombohedron
-on the end, <i>s</i> the opposite rhombohedron, <i>b</i> basal
-face, and the other faces represent bevelings</p>
-</div>
-<div class="pb" id="Page_328">328</div>
-<h3 class="plate" id="Plate_48">Plate 48</h3>
-<div class="img" id="fig122">
-<img src="images/p26.jpg" alt="" width="600" height="474" />
-<p class="pcap">A group of barite crystals</p>
-</div>
-<div class="img" id="fig123">
-<img src="images/p26a.jpg" alt="" width="461" height="169" />
-<p class="pcap">Outline of the typical tabular barite crystal</p>
-</div>
-<div class="img" id="fig124">
-<img src="images/p26b.jpg" alt="" width="230" height="336" />
-<p class="pcap">The six-sided double pyramid,
-composed of three interpenetrating
-crystals, typical of witherite and strontianite</p>
-</div>
-<div class="pb" id="Page_329">329</div>
-<h3 class="plate" id="Plate_44">Plate 44</h3>
-<div class="img" id="fig125">
-<img src="images/p26c.jpg" alt="" width="330" height="343" />
-<p class="pcap">The typical form of analcite</p>
-</div>
-<div class="img" id="fig126">
-<img src="images/p26d.jpg" alt="" width="194" height="376" />
-<p class="pcap">A typical natrolite crystal</p>
-</div>
-<div class="img" id="fig127">
-<img src="images/p26e.jpg" alt="" width="175" height="432" />
-<p class="pcap">The typical crystal form of stilbite</p>
-</div>
-<div class="img" id="fig128">
-<img src="images/p26f.jpg" alt="" width="213" height="438" />
-<p class="pcap">A sheaf-like bundle of fibrous crystals, typical of stilbite</p>
-</div>
-<div class="pb" id="Page_330">330</div>
-<h3 class="plate" id="Plate_45">Plate 45</h3>
-<div class="img" id="fig129">
-<img src="images/p27.jpg" alt="" width="600" height="388" />
-<p class="pcap">A group of calcite crystals</p>
-</div>
-<h4 class="plate">Typical forms of calcite</h4>
-<div class="img" id="fig130">
-<img src="images/p27a.jpg" alt="" width="321" height="259" />
-<p class="pcap"><i>A</i> the rhombohedron formed by cleavage</p>
-</div>
-<div class="img" id="fig131">
-<img src="images/p27b.jpg" alt="" width="304" height="223" />
-<p class="pcap"><i>B</i> a rhombohedral crystal truncated by the basal plane</p>
-</div>
-<div class="img" id="fig132">
-<img src="images/p27c.jpg" alt="" width="194" height="384" />
-<p class="pcap"><i>C</i> the scalenohedron</p>
-</div>
-<div class="img" id="fig133">
-<img src="images/p27d.jpg" alt="" width="185" height="273" />
-<p class="pcap"><i>D</i> the scalenohedron truncated by the rhombohedron</p>
-</div>
-<div class="img" id="fig134">
-<img src="images/p27g.jpg" alt="" width="197" height="398" />
-<p class="pcap"><i>E</i> the scalenohedron on a prism</p>
-</div>
-<div class="pb" id="Page_331">331</div>
-<h3 class="plate" id="Plate_46">Plate 46</h3>
-<h4 class="plate">Typical forms of aragonite</h4>
-<div class="img" id="fig135">
-<img src="images/p27i.jpg" alt="" width="194" height="371" />
-<p class="pcap"><i>A</i> the simple crystal</p>
-</div>
-<div class="img" id="fig136">
-<img src="images/p27l.jpg" alt="" width="75" height="386" />
-<p class="pcap"><i>B</i> a needle-like form, twinned</p>
-</div>
-<div class="img" id="fig137">
-<img src="images/p27m.jpg" alt="" width="178" height="197" />
-<p class="pcap"><i>C</i> cross section to show how the form may appear six-sided</p>
-</div>
-<div class="img" id="fig138">
-<img src="images/p27n.jpg" alt="" width="290" height="129" />
-<p class="pcap">Typical form of the anhydrite crystal</p>
-</div>
-<div class="pb" id="Page_332">332</div>
-<h3 class="plate" id="Plate_47">Plate 47</h3>
-<div class="img" id="fig139">
-<img src="images/p28.jpg" alt="" width="600" height="436" />
-<p class="pcap">A piece of gypsum looking on the surface of the perfect
-cleavage, and showing the two other cleavages as lines,
-intersecting at 66&deg;. Twinning is also shown</p>
-</div>
-<div class="img" id="fig140">
-<img src="images/p28c.jpg" alt="" width="250" height="576" />
-<p class="pcap">A simple crystal of gypsum</p>
-</div>
-<div class="img" id="fig141">
-<img src="images/p28d.jpg" alt="" width="300" height="579" />
-<p class="pcap">Twin crystals of gypsum</p>
-</div>
-<div class="pb" id="Page_333">333</div>
-<h3 class="plate" id="Plate_51">Plate 51</h3>
-<div class="img" id="fig142">
-<img src="images/p28e.jpg" alt="" width="600" height="570" />
-<p class="pcap">Sulphur crystals</p>
-</div>
-<div class="img" id="fig143">
-<img src="images/p28f.jpg" alt="" width="500" height="484" />
-<p class="pcap">Ice crystals, the top one, the end of a hexagonal prism;
-the two lower figures multiple twins as in snow flakes</p>
-</div>
-<div class="pb" id="Page_334">334</div>
-<h3 class="plate" id="Plate_52">Plate 52</h3>
-<div class="img" id="fig144">
-<img src="images/p29.jpg" alt="" width="465" height="901" />
-<p class="pcap">The Devil&rsquo;s Tower, Wyoming, an example of igneous
-rock with columnar structure, and resting on sedimentary
-rocks. Courtesy of the U. S. Geological Survey</p>
-</div>
-<div class="pb" id="Page_335">335</div>
-<h3 class="plate" id="Plate_53">Plate 53</h3>
-<div class="img" id="fig145">
-<img src="images/p29b.jpg" alt="" width="600" height="406" />
-<p class="pcap">A coarse granite</p>
-</div>
-<div class="img" id="fig146">
-<img src="images/p29c.jpg" alt="" width="600" height="365" />
-<p class="pcap">Graphic granite</p>
-</div>
-<div class="pb" id="Page_336">336</div>
-<h3 class="plate" id="Plate_54">Plate 54</h3>
-<div class="img" id="fig147">
-<img src="images/p30.jpg" alt="" width="600" height="554" />
-<p class="pcap">Syenite</p>
-</div>
-<div class="img" id="fig148">
-<img src="images/p30a.jpg" alt="" width="600" height="457" />
-<p class="pcap">Gabbro</p>
-</div>
-<div class="pb" id="Page_337">337</div>
-<h3 class="plate" id="Plate_55">Plate 55</h3>
-<div class="img" id="fig149">
-<img src="images/p30c.jpg" alt="" width="600" height="429" />
-<p class="pcap">Basalt-porphyry. The large white crystals are phenocrysts
-of plagioclase feldspar</p>
-</div>
-<div class="img" id="fig150">
-<img src="images/p30d.jpg" alt="" width="600" height="529" />
-<p class="pcap">Basalt-obsidian</p>
-</div>
-<div class="pb" id="Page_338">338</div>
-<h3 class="plate" id="Plate_56">Plate 56</h3>
-<div class="img" id="fig151">
-<img src="images/p31.jpg" alt="" width="600" height="482" />
-<p class="pcap">Amgydoloid</p>
-</div>
-<div class="pb" id="Page_339">339</div>
-<h3 class="plate" id="Plate_57">Plate 57</h3>
-<div class="img" id="fig152">
-<img src="images/p31a.jpg" alt="" width="500" height="887" />
-<p class="pcap">The north face of Scott&rsquo;s Bluff, Neb., showing sedimentary
-sandstones above and clays below. The type of
-erosion is characteristic of arid regions. Courtesy of
-the U. S. Geological Survey</p>
-</div>
-<div class="pb" id="Page_340">340</div>
-<h3 class="plate" id="Plate_58">Plate 58</h3>
-<div class="img" id="fig153">
-<img src="images/p32.jpg" alt="" width="600" height="503" />
-<p class="pcap">Breccia</p>
-</div>
-<div class="img" id="fig154">
-<img src="images/p32a.jpg" alt="" width="600" height="470" />
-<p class="pcap">Conglomerate</p>
-</div>
-<div class="pb" id="Page_341">341</div>
-<h3 class="plate" id="Plate_59">Plate 59</h3>
-<div class="img" id="fig155">
-<img src="images/p32c.jpg" alt="" width="600" height="531" />
-<p class="pcap">Calcareous shale</p>
-</div>
-<div class="img" id="fig156">
-<img src="images/p32d.jpg" alt="" width="600" height="374" />
-<p class="pcap">Coquina</p>
-</div>
-<div class="pb" id="Page_342">342</div>
-<h3 class="plate" id="Plate_60">Plate 60</h3>
-<div class="img" id="fig157">
-<img src="images/p33.jpg" alt="" width="600" height="497" />
-<p class="pcap">Foramenifera from Chalk; enlarged about 25 diameters</p>
-</div>
-<div class="img" id="fig158">
-<img src="images/p34.jpg" alt="" width="600" height="483" />
-<p class="pcap">Encrinal Limestone; fragments of the stems, arms and
-body of Crinoids</p>
-</div>
-<div class="pb" id="Page_343">343</div>
-<h3 class="plate" id="Plate_62">Plate 62</h3>
-<div class="img" id="fig159">
-<img src="images/p35.jpg" alt="" width="483" height="502" />
-<p class="pcap"><i>A</i> diatomaceous earth magnified 50 times</p>
-</div>
-<div class="img" id="fig160">
-<img src="images/p36.jpg" alt="" width="279" height="600" />
-<p class="pcap"><i>B</i> and <i>C</i> two diatoms from
-the above enlarged 250 times. After
-Gravelle, by the courtesy of Natural History</p>
-</div>
-<div class="pb" id="Page_344">344</div>
-<h3 class="plate" id="Plate_63">Plate 63</h3>
-<div class="img" id="fig161">
-<img src="images/p38.jpg" alt="" width="900" height="480" />
-<p class="pcap">A metamorphic rock, showing the contortion of layers due to expansion under heat</p>
-</div>
-<div class="pb" id="Page_345">345</div>
-<h3 class="plate" id="Plate_64">Plate 64</h3>
-<div class="img" id="fig162">
-<img src="images/p38a.jpg" alt="" width="600" height="349" />
-<p class="pcap">A conglomerate partly metamorphosed to a gneiss. Note
-the flattened pebbles and the alternation of the intermediate
-material to mica scales, etc.</p>
-</div>
-<div class="img" id="fig163">
-<img src="images/p38d.jpg" alt="" width="600" height="659" />
-<p class="pcap">A typical gneiss</p>
-</div>
-<div class="pb" id="Page_346">346</div>
-<h3 class="plate" id="Plate_66">Plate 66</h3>
-<div class="img" id="fig164">
-<img src="images/p39.jpg" alt="" width="600" height="400" />
-<p class="pcap">Phyllite</p>
-</div>
-<div class="img" id="fig165">
-<img src="images/p39a.jpg" alt="" width="600" height="643" />
-<p class="pcap">A white marble, with black streaks due to graphite</p>
-</div>
-<div class="pb" id="Page_347">347</div>
-<h3 class="plate" id="Plate_68">Plate 68</h3>
-<div class="img" id="fig166">
-<img src="images/p39c.jpg" alt="" width="600" height="512" />
-<p class="pcap">Claystones, simple and compound</p>
-</div>
-<div class="img" id="fig167">
-<img src="images/p39d.jpg" alt="" width="600" height="564" />
-<p class="pcap">A line concretion, which on splitting disclosed a fern leaf
-of the age of the coal measures</p>
-</div>
-<div class="pb" id="Page_348">348</div>
-<h3 class="plate" id="Plate_69">Plate 69</h3>
-<div class="img" id="fig168">
-<img src="images/p40.jpg" alt="" width="600" height="542" />
-<p class="pcap">A septeria from Seneca Lake, N. Y.</p>
-</div>
-<div class="img" id="fig169">
-<img src="images/p40a.jpg" alt="" width="600" height="666" />
-<p class="pcap">Pisolite</p>
-</div>
-<div class="pb" id="Page_349">349</div>
-<h3 class="plate" id="Plate_70">Plate 70</h3>
-<div class="img" id="fig170">
-<img src="images/p40c.jpg" alt="" width="600" height="622" />
-<p class="pcap">A geode filled with quartz crystals</p>
-</div>
-<div class="pb" id="Page_350">350</div>
-<h3 class="plate" id="Plate_71">Plate 71</h3>
-<div class="img" id="fig171">
-<img src="images/p41.jpg" alt="" width="600" height="472" />
-<p class="pcap">A quartz pebble from the bed of a New England brook</p>
-</div>
-<div class="img" id="fig172">
-<img src="images/p41a.jpg" alt="" width="600" height="527" />
-<p class="pcap">A pebble of schist and granite from the foot of Mt. Toby,
-Mass.</p>
-</div>
-<div class="pb" id="Page_351">351</div>
-<h3 class="plate" id="Plate_72">Plate 72</h3>
-<div class="img" id="fig173">
-<img src="images/p41c.jpg" alt="" width="600" height="436" />
-<p class="pcap">An iron-nickel meteorite, of 23 lbs. which fell in Claiborne
-Co., Tenn.</p>
-</div>
-<div class="img" id="fig174">
-<img src="images/p41d.jpg" alt="" width="600" height="524" />
-<p class="pcap">An etched slice of an iron meteorite which fell in Reed
-City, Osceola Co., Mich.</p>
-</div>
-<div class="pb" id="Page_352">352</div>
-<h3 class="plate" id="Plate_73">Plate 73</h3>
-<div class="img" id="fig175">
-<img src="images/p42.jpg" alt="" width="800" height="562" />
-<p class="pcap">A stony meteorite, about natural size, which fell in 1875, in Iowa Co., Iowa</p>
-</div>
-<hr />
-<h3 class="center">PUTNAM&rsquo;S
-<br />NATURE FIELD BOOKS
-<br />Companion books to this one</h3>
-<table class="center" summary="">
-<tr><td class="l">Mathews </td><td class="l">American Wild Flowers</td></tr>
-<tr><td class="l"> </td><td class="l">American Trees and Shrubs</td></tr>
-<tr><td class="l"> </td><td class="l">Wild Birds and Their Music</td></tr>
-<tr><td class="l">Durand </td><td class="l">Wild Flowers in Homes and Gardens</td></tr>
-<tr><td class="l"> </td><td class="l">My Wild Flower Garden</td></tr>
-<tr><td class="l"> </td><td class="l">Common Ferns</td></tr>
-<tr><td class="l">Lutz </td><td class="l">Insects</td></tr>
-<tr><td class="l">Loomis </td><td class="l">Rocks and Minerals</td></tr>
-<tr><td class="l">Eliot </td><td class="l">Birds of the Pacific Coast</td></tr>
-<tr><td class="l">Armstrong </td><td class="l">Western Wild Flowers</td></tr>
-<tr><td class="l">Alexander </td><td class="l">Birds of the Ocean</td></tr>
-<tr><td class="l">Anthony </td><td class="l">North American Mammals</td></tr>
-<tr><td class="l">Thomas </td><td class="l">Common Mushrooms</td></tr>
-<tr><td class="l">Sturgis </td><td class="l">Birds of the Panama Canal Zone</td></tr>
-<tr><td class="l">Miner </td><td class="l">Seashore Life</td></tr>
-<tr><td class="l">Breder </td><td class="l">Marine Fishes of the Atlantic Coast</td></tr>
-<tr><td class="l">Morgan </td><td class="l">Ponds and Streams</td></tr>
-<tr><td class="l">Longyear </td><td class="l">Rocky Mountain Trees and Shrubs</td></tr>
-<tr><td class="l">Olcott<br />Putnam </td><td class="l">Field Book of the Skies</td></tr>
-<tr><td class="l">Beebe<br />Tee-Van </td><td class="l">The Shore Fishes of Bermuda</td></tr>
-<tr><td class="l">Schrenkeisen </td><td class="l">Fresh-Water Fishes of North America North of Mexico</td></tr>
-</table>
-<h2>Transcriber&rsquo;s Notes</h2>
-<ul>
-<li>Retained publication information from the printed edition: this eBook is public-domain in the country of publication.</li>
-<li>In the text versions only, text in italics is delimited by _underscores_.</li>
-<li>Silently corrected a few typos.</li>
-<li>Reconstructed an image caption (Pisolite) on Plate 69.</li>
-<li>Generated a cover image based on elements in the book.</li>
-</ul>
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