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diff --git a/old/55382-0.txt b/old/55382-0.txt deleted file mode 100644 index 10da295..0000000 --- a/old/55382-0.txt +++ /dev/null @@ -1,10133 +0,0 @@ -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 - -*** END OF THIS PROJECT GUTENBERG EBOOK FIELD BOOK OF COMMON ROCKS *** - -***** This file should be named 55382-0.txt or 55382-0.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/5/5/3/8/55382/ - -Produced by Stephen Hutcheson, Dave Morgan and the Online -Distributed Proofreading Team at http://www.pgdp.net - -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the United -States without permission and without paying copyright -royalties. 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