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diff --git a/old/60070-8.txt b/old/60070-8.txt deleted file mode 100644 index 7720624..0000000 --- a/old/60070-8.txt +++ /dev/null @@ -1,2940 +0,0 @@ -The Project Gutenberg EBook of Texas Gemstones, by Elbert A. King, Jr. - -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: Texas Gemstones - -Author: Elbert A. King, Jr. - -Release Date: August 6, 2019 [EBook #60070] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK TEXAS GEMSTONES *** - - - - -Produced by Stephen Hutcheson and the Online Distributed -Proofreading Team at http://www.pgdp.net - - - - - - - - - - BUREAU OF ECONOMIC GEOLOGY - The University of Texas at Austin - Austin, Texas 78712 - - JOHN T. LONSDALE, _Director_ - - - Report of Investigations--No. 42 - - - - - Texas Gemstones - - - By - Elbert A. King, Jr. - - February 1961 - - _Second Printing--February 1963 - Third Printing--September 1972 - Fourth Printing--March 1983 - Fifth Printing--August 1991_ - - - - - Contents - - - Page - Introduction 5 - Properties of gemstones 5 - Crystals 7 - Cutting and polishing of gemstones 10 - Cabochon gems 10 - Faceted gems 13 - Tumbled gems 17 - Texas gemstones 18 - Amber 18 - Augite 18 - Beryl 18 - Celestite 19 - Diamond 19 - Epidote 19 - Fluorite 20 - Fossil wood 20 - Gadolinite 21 - Garnet 22 - Jet 22 - Labradorite 23 - Microcline 23 - Obsidian 24 - Opal 24 - Pearl 24 - Quartz 25 - Crystalline varieties 25 - Amethyst 25 - Citrine 25 - Rock crystal 26 - Rose quartz 26 - Smoky quartz 26 - Cryptocrystalline varieties 27 - Chalcedony 27 - Agate 27 - Agatized wood 27 - Carnelian 27 - Jasper 27 - Sanidine 28 - Spinel 28 - Tektite (bediasite) 28 - Topaz 29 - Tourmaline 30 - Turquoise 31 - Glossary 32 - Selected references 34 - Index 41 - - - - - Illustrations - - - Figures-- Page - 1. Typical crystal form of three common Texas gemstones 9 - 2. Variations of the cabochon cut 10 - 3. Diamond saw 11 - 4. Cabochon properly attached to dop-stick 12 - 5. Cabochons at various stages of cutting and polishing 12 - 6. Nomenclature of the standard American brilliant cut 13 - 7. Facet table 14 - 8. Grinding the table facet on a rough stone 15 - 9. Stone dopped to table facet 15 - 10. Preformed stone dopped to table facet 16 - 11. Proper sequence of cutting of the pavilion facets 16 - 12. Proper placing of pavilion girdle facets 17 - 13. Proper sequence of cutting of crown facets 17 - 14. Common crystal form of Travis County celestite 19 - 15. Common crystal form of fluorite 20 - 16. Crystal faces on microcline specimen shown in Plate III 23 - 17. Common crystal form of spinel 28 - 18. Crystal faces on topaz crystal shown in Plate V 29 - 19. Cross section through irregularly colored stone 30 - 20. Common crystal form of Llano County tourmaline 31 - - - Plates-- Page - I. A, Gem-quality celestite crystals from Travis County. B, - Opalized wood from the Texas Gulf Coastal Plain 35 - II. A, Gem-quality garnet crystals and faceted gem from Gillespie - County. B, Labradorite from Brewster County 36 - III. A, Pink microcline crystal. B, Smoky quartz. Both from Burnet - County 37 - IV. Polished agate from gravels of the Rio Grande near Zapata, - Zapata County 38 - V. A, Texas tektites (bediasites). B, Topaz crystal from a - pegmatite dike near Streeter, Mason County 39 - VI. A, Topaz from stream gravels near Streeter, Mason County. B, - Tourmaline crystals in schist from Llano County 40 - - - Table 1. Properties of some common Texas gem minerals 8 - - - - - Texas Gemstones - - - ELBERT A. KING, JR. - - - - - INTRODUCTION - - -Throughout history man has sought stones and minerals for personal -adornment and ornamentation. Stones and minerals that are sufficiently -beautiful, durable, and rare are known as gemstones. A gemstone with -only one of these qualities is less desirable than one with all three. -For example, a stone with rich color but not sufficiently durable to -withstand daily wear in rings finds little favor as a gemstone except in -brooches or pins where the stone is relatively safe from abrasion. -Likewise, a stone that is beautiful and durable may be of little -interest as a gemstone because it is commonly found in great quantities. -To be valued highly, gemstones must be beautiful to the eye, durable -enough to withstand wear, and rare enough so that they are not easily -obtained. - - - - - Properties of Gemstones - - -The beauty of gemstones is mostly dependent on their color, diaphaneity, -brilliancy, luster, and fire. Any one or a combination of these -properties render stones desirable as gems. - -Color is very important in many gemstones. The color of transparent -varieties should be distinct enough to be pleasing to the eye, yet not -so dark as to appear black or opaque. It is generally more desirable -that the gemstone be of even color and not appear "patchy" or -"streaked." However, some opaque or translucent stones such as agate owe -their popularity chiefly to the variety of colors and designs within a -single piece. Some transparent gemstones exhibit different colors when -viewed in different directions. For example, some fine blood-red rubies -appear brownish when viewed in a particular direction. The gemstone -should be cut so that its finest color is most prominently displayed. -This ability of some gemstones to exhibit different colors when viewed -in different directions is called pleochroism. - -Diaphaneity is the relative ability of stones to transmit light. -Diaphaneity is described by terms such as transparent, translucent, and -opaque. Transparency is highly desirable in stones such as diamond that -are commonly facet-cut to reflect light. The gemstone should be water -clear and free from inclusions and cracks so that it transmits light -freely, but there are stones that do not exhibit this property that are -prized as gemstones. For example, turquoise may appear to be completely -opaque and not transmit any light, but it is sought for its fine blue -color. - -The brilliancy of gemstones is largely dependent on their index of -refraction. The index of refraction is a measure of the ability of a cut -gemstone to "bend" light rays and reflect them from the bottom facets -back through the top of the stone. Of course, brilliancy is not noted in -opaque or faintly translucent stones. The index of refraction of -gemstones is expressed numerically. Air is the reference medium and is -assigned an index of refraction of 1.00. Other substances are assigned -values relative to that of air, for example, water, 1.33; topaz, 1.62; -diamond, 2.42. The higher the index of refraction, the more brilliant -will be the gemstone if it is properly cut and polished. - -Luster is the appearance of the mineral on a fresh surface in reflected -light; it is divided into two major categories, metallic and -non-metallic. Most gemstones have non-metallic luster and are described -by terms such as vitreous or glassy, resinous, waxy, greasy, and pearly. - -The fire, or ability of gemstones to show flashes of different colors of -light, is dependent upon a property called dispersion. The amount of -dispersion is the extent to which the gemstone is able to separate -ordinary white light into its component colors. The dispersion of -gemstones can also be expressed numerically but for purposes of this -publication will be referred to as low, moderate, or high. Diamond is a -common gemstone that has high dispersion. - -A gemstone's durability is primarily dependent upon its hardness. The -Mohs scale of hardness, given below, is most commonly used for gemstones -and other minerals. - - _Mohs Scale of Hardness_ - 1. Talc - 2. Gypsum - 3. Calcite - 4. Fluorite - 5. Apatite - 6. Orthoclase feldspar - 7. Quartz - 8. Topaz - 9. Corundum - 10. Diamond - -On this scale, the higher numbers are the harder minerals. Mohs is a -relative, not an absolute scale. Therefore, it should not be assumed -that diamond is ten times harder than talc because actually diamond is -very many tens of times harder than talc. However, a particular mineral -is harder than any other mineral with a lesser number, and the scale is -very convenient to use. Gemstones mounted in rings should have a -hardness of at least seven on the Mohs scale, or the stones may become -scuffed and scratched after a relatively short period of wear. Gemstones -mounted in pins and brooches can be of softer material as they are not -usually subjected to abrasion and rough treatment. - -The tendency of some minerals to split with relative ease in particular -directions along planes is called cleavage. Cleavage is also a factor -determining the durability of gemstones. Some gemstones do not exhibit -this tendency at all, whereas others cleave in several directions. The -number of cleavages is always the same in any one mineral, and the -direction of cleavages is constant in relation to the crystal structure -of any one mineral or gemstone. It is apparent that of stones having the -same hardness, the ones lacking cleavage or having the lesser number of -good cleavage directions are the most durable. - -Some stones, such as jade and agate, owe their durability to their -compact fibrous structure, which makes them very tough and durable even -though they are not especially hard. - -Several other properties of gemstones, although not always contributing -to the beauty or desirability of gemstones, are useful in identifying -uncut specimens. - -Streak is the color of the mineral when finely powdered or, for softer -minerals, the color obtained by rubbing the mineral against a piece of -unglazed porcelain or tile. The color of a mineral's streak is commonly -different from the unpowdered specimen. - -Fracture is the kind of surface obtained when the mineral is broken in a -direction that is not a cleavage direction. Fracture surfaces are -described by such terms as conchoidal (like the fracture of glass), -subconchoidal, splintery, even, and uneven. - -Tenacity is the resistance of a mineral to breakage. Brittle minerals -break relatively easily on impact. Malleable minerals, such as gold, may -be flattened under a hammer into very thin sheets without breaking. -Sectile minerals may be cut with a knife without powdering. Most -gemstones, even diamond, are brittle. - -It is only natural to value most those gemstones that are not common or -easy to obtain. Emerald owes its longstanding popularity to its fine -green color, but tourmaline is sometimes found in colors that very -closely approach that of emerald and yet sells for considerably less -because it is so much more common. - -Rarity is not the only factor affecting the value of gemstones. Freedom -from internal imperfections, quality of cutting, color, and size must -also be considered in cut and polished gemstones. Internal -imperfections, such as inclusions and cracks, detract from the -appearance of gemstones and interfere with the passage of light between -the facets; consequently, gemstones containing these imperfections are -not valued as highly as those without them. Poor cutting or polishing -detract from the beauty and thus from the value of gemstones. Unpopular -or poor color commonly causes gemstones to be less valuable. Rich green -emeralds are exceedingly prized, whereas very pale green emeralds are -relatively inexpensive. Diamonds that have the least hint of yellow are -never valued as highly as pure colorless, pink, or blue stones. Few -persons find the yellowish color attractive, unless it is a vivid canary -yellow. - -Size is important in determining the value of gemstones but not as -important as perfection. A badly flawed gemstone of large size may be -worth only a slight fraction of the value of a smaller perfect one. -Gemstone size is usually measured in carats, a unit of weight, although -millimeter size is sometimes used. Five carats is equal to 1 gram and -approximately 28-1/3 grams is equal to 1 ounce avoirdupois. One -one-hundredth (0.01) of a carat is called a point, and this term is -often used, especially pertaining to very small gemstones. - -The term used to compare the relative weights of minerals and gemstones -is specific gravity, which is expressed numerically in relation to -water. Water is assigned the value of 1.00. Therefore, at a given -temperature a gemstone having a specific gravity of 2.00 is twice as -heavy as an equal volume of water. A 1-carat sapphire (specific gravity -about 4.00) will be smaller than a 1-carat amethyst (specific gravity -about 2.65) because the heavier material will occupy less volume to have -the same weight. - -A summary of properties helpful in identification of common Texas gem -minerals is given in Table 1. - -Comparatively recently in the history of gemstones, man has succeeded in -the production of synthetic gems that have properties closely -approaching those of many natural gemstones. To the untrained eye some -synthetic gems may appear identical to natural stones, but synthetic -gems can be detected with little difficulty by a properly equipped -expert. Although most synthetic gems are inexpensive, their manufacture -has not adversely affected the value of natural gemstones but instead -has increased the demand for fine natural gems. - - - - - Crystals - - -Gemstones that have an orderly internal molecular arrangement are -referred to as crystalline. This internal order is commonly reflected in -the external shape of "rough" or uncut gemstones. The resultant shape is -a polyhedral solid bounded by planes and called a crystal. Well-formed -crystals are formed in nature only under relatively ideal conditions of -temperature, pressure, and space. The specific temperatures and -pressures involved vary with different minerals, but most crystals need -space in which to form so that their "growth" is not impaired by -surrounding rocks and minerals. However, some minerals, such as garnet -and tourmaline, can grow in metamorphic rocks by recrystallization of -minerals in the metamorphic rocks. The size of crystals varies from -microscopic to tens of feet. Any one mineral usually has one or two -typical crystal forms or arrangements of plane surfaces that aid greatly -in the identification of the mineral when it occurs in good crystals -(fig. 1). Frequently gemstones are found as abraded stream-rolled -pebbles, fragments, or masses that do not show crystal form. Crystals of -the same mineral from different locations commonly show somewhat -different crystal forms owing to slight differences in composition or -conditions of formation. Mineralogists and crystallographers classify -crystals by the symmetry that they exhibit. The crystal systems are (1) -isometric or cubic, (2) tetragonal, (3) hexagonal, (4) orthorhombic, (5) -monoclinic, and (6) triclinic. A complete description of the -classification of crystals can be found in almost any mineralogy text -(see Selected References, p. 34). - - Table 1. Properties of some common Texas gem minerals. - MINERAL COMPOSITION HARDNESS SPECIFIC INDEX OF COMMON - GRAVITY REFRACTION COLORS IN - TEXAS - - Amber fossil resin 2.0-2.5 1.05-1.10 about 1.54 brown, yellow - Augite CaMgSi_2O_6 5.0-6.0 3.2-3.6 1.60-1.71 greenish - brown, black - Beryl Be_3Al_2(SiO)_6 7.5-8.0 2.63-2.80 1.56-1.60 pale blue, - colorless, - greenish - Celestite SrSO_4 3.0-3.5 3.95-3.98 1.62-1.63 colorless, - blue - Epidote HCa_2(Al, 6.0-7.0 3.25-3.50 1.72-1.77 yellowish - Fe)_3Si_3O_1_3 green, - brownish - green - Fluorite CaF_2 4.0 3.0-3.25 1.434 colorless, - violet, - yellow, green - Garnet Fe_3Al_2(SiO_4)_3 about 7.5 4.25 about 1.83 red, deep - (Almandite) red, - brownish red - Labradorite NaAlSi_3O_8 50% to 6.0-6.5 about 2.6 about 1.56 yellowish, - 30% CaAlSi_3O_8 50% grayish - to 70% - Microcline KAlSi_3O_8 6.0-6.5 2.54-2.57 1.52-1.53 pink, red, - bluish, - greenish, - white - Obsidian volcanic glass 5.0-5.5 2.3-2.5 1.45-1.53 dark gray, - black, - brownish - Opal SiO_2·nH_2O 5.5-6.5 1.9-2.3 1.43 white, pink, - bluish, - brown, gray - Quartz SiO_2 7.0 2.65-2.66 1.544-1.553 colorless, - (Crystalline) violet, - yellow, brown - Tektite natural glass 5-6 2.33-2.44 1.48-1.52 dark brown, - (Bediasite) greenish - brown - Topaz Al_2(F·OH)_2SiO_4 8.0 3.4-3.6 1.60-1.63 colorless, - bluish, sky - blue - Tourmaline H_9Al_3(B·OH)_2Si_4O_1_9 7.0-7.5 2.98-3.20 1.62-1.64 black, dark - brown - -Some gemstones, such as opal and obsidian, never occur as crystals owing -to a lack of internal structural order. Such gemstones are termed -amorphous, or without form. Amorphous gemstones mostly occur in nature -as irregular lumps or masses, cavity fillings, or veins. - - [Illustration: Fig. 1. Typical crystal form of three common Texas - gemstones.] - - GARNET - TOURMALINE - QUARTZ - - - - - CUTTING AND POLISHING OF GEMSTONES - - -There are two types of widely used gemstone cuts. Opaque or figured -gemstones are usually cut with a rounded upper surface and a flat or -rounded back. A stone cut in this fashion is termed a cabochon or is -said to be cabochon cut. There are several variations of this mode of -cutting (fig. 2). Precious opal, agate, jade, star sapphire, and fossil -wood are some of the stones that are cut mostly as cabochons. -Transparent gemstones are usually cut with many plane polished surfaces. -Such stones are called faceted, and the process of cutting and polishing -these stones is called faceting. Emerald, diamond, topaz, and garnet are -examples of gemstones that are commonly seen as faceted stones. - - [Illustration: Fig. 2. Variations of the cabochon cut. Left to right: - double cabochon; flat cabochon; simple cabochon; hollow cabochon.] - -The cutting of gemstones, although sometimes tedious and time consuming, -is not especially difficult or complex. However, like most arts and -crafts, technique and ability should improve with practice and -experience. There are currently many amateur gem cutters in Texas. A -complete set of equipment necessary to cut cabochon stones may be -purchased for as little as $50.00 or $60.00. Most amateur cabochon -cutters have equipment that cost less than $100.00 which enables them to -do very fine work on many gem materials. Facet cutting requires more -precise equipment, and a complete array of such usually costs more than -$100.00, although less expensive equipment can be obtained. The -beginning gem cutter or lapidary who is willing to assemble and make -some of his own equipment can reduce his initial expenses considerably. - - - - - Cabochon Gems - - -The procedures listed herein for gem cutting do not apply to all -gemstones. Stones that are especially brittle, soft, or difficult to -polish require additional procedures or special techniques. Many -lapidaries may deviate from these procedures. Some of the steps of -cutting and polishing are merely matters of personal opinion and vary -somewhat from cutter to cutter. There are several detailed texts on the -art of gem cutting; the descriptions herein are designed to give the -reader only a general idea of the procedures and techniques involved. - -The cutting and polishing of cabochons require several steps. The -initial step is sawing. Assuming that the rough gem material is large -enough to be sawed (larger than about half an inch in diameter), it is -clamped into the carriage of a diamond saw (fig. 3) and cut into slices -about 3/8-inch thick. The blade of the saw is mild steel that has been -impregnated with diamond dust around the edge, hence the name diamond -saw. The blade is rotated rapidly, and the material to be cut is "fed" -to the blade by a sliding carriage on which the gem material is clamped. -The extreme hardness of the diamond dust in the edge of the blade -enables the saw to cut through several inches of gem material in a few -minutes. The lower portion of the saw blade is immersed in a mixture of -kerosene and oil, and the rotating saw blade carries with it some of the -kerosene-oil mixture; this acts as a coolant and lubricant for both the -saw blade and the material being cut. Without this lubricant, the heat -generated by sawing would shatter most gem materials and also damage the -saw blade. As this "slicing" or sawing of the material usually takes -several minutes, a weight and pulley are generally used to give the gem -material the necessary pressure against the saw blade. When cut through, -the "slab" of gem material falls into the kerosene-oil mixture at the -bottom of the saw or onto a special platform that cushions its fall. - - [Illustration: Fig. 3. Diamond saw.] - - Motor - Clamp - Diamond-charged blade - Carriage - Stone - Weight - -After being sawed, the slab of gem material is examined, and the -location and size of the stones to be cut from the slab are determined. -The desired outline of the shape of the gem to be cut is marked on the -slab with a pointed piece of aluminum rod; ordinary pencil marks are not -used because they wear away too quickly in the cutting process. Once the -area from which the gem is to be cut has been selected and the outline -of the gemstone has been marked on the slab, the excess material is -trimmed away by a smaller diamond saw known as a trim-saw. In some slabs -the excess material can be broken and "nibbled" away with a strong pair -of pliers. - -The remaining portion of the stone is usually held by hand and ground to -the desired shape using the previously scribed mark as a guide. This is -done using a relatively coarse-grained (about 150 grit) specially made -carborundum grinding wheel. - -Now that the desired outline has been obtained, the stone is firmly -affixed to a slender wooden or hollow aluminum dop-stick (fig. 4). The -process whereby the stone is attached to the dop-stick with a specially -compounded jeweler's wax is called dopping. The dop-wax is heated over -an alcohol lamp or candle flame until it is soft and pliable and is then -spread around on the end of the dop-stick and formed into a mass about -the right size and shape to fit the back of the gemstone. The stone is -likewise heated, and the wax is applied to the back of the stone while -both wax and stone are hot. Upon cooling, the wax firmly fixes the stone -to the dop-stick. The dop-stick allows the lapidary to have firm control -of the stone during all later stages of cutting and polishing. - - [Illustration: Fig. 4. Cabochon properly attached to dop-stick.] - - CABOCHON - DOP-WAX - DOP-STICK - -The top of the dopped gemstone is worked against the coarse carborundum -grinding wheel until it is a rough approximation of the desired shape. -The stone is then worked against a much finer-grained (about 220 grit) -grinding wheel to remove the irregularities left by the coarse grinding -and to further smooth and shape the surface of the gemstone. At all -times while grinding, a small flow of water should be directed on the -grinding wheel to keep the stone cool. Grinding on the stone for even a -few minutes without cooling may result in the shattering of the gemstone -because of heat created by friction of the stone against the grinding -wheel. If the lapidary keeps the surface of the grinding wheel wet, -there is little chance of damaging most gem materials. - -The next phase of cabochon cutting and polishing is sanding. The -gemstone is worked against two sanding drums of different grit size. -This sanding can be done with the sandpaper surface either wet or dry, -as needed or as preferred by the lapidary. However, great care should be -exercised during sanding so that the stone is not overheated. -Overheating can easily occur whether the sandpaper is used wet or dry. -As in grinding, sanding is first done on coarser grit paper (about 300 -grit) and last on finer paper (about 600 grit). It is in the sanding -process that the first hint of polish is noted on the surface of the -stone. After sanding, the gemstone should have perfect form with no -surface irregularities, a very finely textured surface, and only very -minor scratches left from sanding. The gemstone is now ready to be -polished. - - [Illustration: Fig. 5. Cabochons at various stages of cutting and - polishing. Left to right: trimmed from slab: ground to outline; after - rough grinding; after sanding; polished.] - -At this point the procedure depends on the nature of the gemstone being -polished. Most gem materials are worked against a buffing wheel that is -impregnated or saturated with a mixture of some polishing compound and -water. A soft felt buffing wheel with cerium oxide as the polishing -agent is used for many materials. The mixture of cerium oxide and water -is usually applied to the buffing wheel with a small brush. The lapidary -should once more be careful not to overheat the stone. If the stone -becomes too hot to hold to the underside of the cutter's wrist, it -should be permitted to cool for a few seconds before continuing. After -polishing on the buffing wheel, the gemstone should have a fine, high -polish and be free of any scratches or surface irregularities. The -finished gemstone is removed from the dop-stick by heating the dop-wax -and pulling the stone loose. Any excess wax that hardens again before it -can be removed from the stone by hand can be dissolved away by rubbing -with an acetone-soaked cloth. Figure 5 illustrates the desired -appearance of the gemstone at the end of each of the steps of cutting -and polishing. - - - - - Faceted Gems - - -The principles involved in faceting are about the same as those in the -cutting of cabochons, but the equipment and technique are considerably -different. The equipment required for the facet cutting of gemstones is -built into or attached to a small specially constructed table (fig. 7), -and the unit is commonly called a facet table. Most faceted gemstones -are cut to obtain the largest flawless stone possible from the rough -material. Therefore, one of the first and most important steps for the -lapidary is to decide how the stone is to be cut from the rough crystal -or pebble. The colors that can be obtained from the gemstone must also -be considered, and the cutting of the stone oriented so that its best -color is displayed. The lapidary also selects the orientation of the -stone in relation to the cleavage or cleavages. It is difficult or -impossible to polish facets of gemstones that are cut parallel to a good -cleavage direction. - - [Illustration: Fig. 6. Nomenclature of the standard American brilliant - cut.] - - TOP VIEW - SIDE VIEW - Star facet - Crown main facet - Crown girdle facet - Pavilion girdle facet - Pavilion main facet - TABLE - CROWN GIRDLE - PAVILION - CULET - BOTTOM VIEW - -Once the orientation of the gemstone to be cut from the rough material -has been determined, the stone is dopped onto a special metal dop-stick -that fits into the chuck of the facet head. The chuck is tightened so -that the position of the stone on the end of the arm of the facet head -is firmly fixed, and the facet head is adjusted so that the first facet -that is cut is the horizontal, top facet of the stone or table facet -(fig. 6). The table facet is cut by grinding the gemstone on a flat -cutting lap that is diamond impregnated (fig. 8). By minor adjustments -of the facet head, the lapidary can precisely control the location of -the table facet. As soon as the table facet has been ground to the -proper size, the cutting lap is removed from the lap plate, and the -polishing lap is secured in place. Many different kinds of polishing -laps and polishing compounds may be used depending on the properties of -the material being polished. However, one lap and one polishing compound -are usually sufficient for each gem variety. After the polishing lap is -secured to the lap plate, the lapidary adjusts the facet head so that -the stone is in exactly the same position relative to the lap that it -was during the cutting of the table facet. The polishing lap is run wet -or damp with water, as is the cutting lap, and small amounts of the -polishing compound are applied to the surface of the lap while the facet -is being polished. The minor scratches left by the cutting process are -gradually removed, and a fine lustrous polish develops on the facet. It -is especially important to take care in achieving a perfect polish on -the table facet, as this facet occupies a large area of the crown of the -gemstone. When the cutting and polishing of the table facet are -completed, the gemstone is still rough or uncut in all portions except -for this single, large, polished surface. - - [Illustration: Fig. 7. Facet table.] - - Water - Light - Adjusting ring - Post - Arm - Chuck - Stone - Abrasives - DIAMOND DUST - CALCIUM OXIDE - LANDE-A - - [Illustration: Fig. 8. Grinding the table facet on a rough stone.] - - CHUCK - DOP-STICK - DOP-WAX - STONE - LAP - -The gemstone is then removed from the dop-stick by melting the dop-wax -and is dopped once more so that the plane of the polished table facet is -perpendicular to the axis of the chuck and arm of the facet head (fig. -9). Great care should be taken by the lapidary to insure that the table -of the stone is exactly perpendicular to this axis, or the proper -placing of the later facets on the stone may become very difficult. - - [Illustration: Fig. 9. Stone dopped to table facet.] - - TABLE FACET - DOP-WAX - STONE - DOP-STICK - -Once the stone has been properly dopped to the table facet, the lapidary -is ready to proceed with the cutting of the outline of the stone. If it -is to be a brilliant cut, the stone is ground perfectly round in -outline; if it is to be an emerald or step cut, it is shaped so that it -is square or rectangular in outline. This process is called preforming. -The arm of the facet head is lowered on the post until it is horizontal, -and the stone is worked against the cutting lap until the desired shape -is obtained. When the preforming process is completed, the stone should -have the desired outline of the finished gem (fig. 10). - - [Illustration: Fig. 10. Preformed stone dopped to table facet.] - - DOP-WAX - STONE - DOP-STICK - -The lapidary is now ready to proceed with the cutting of the pavilion of -the stone. The arm of the facet head is raised to the proper angle for -cutting the main pavilion facets. The angle at which the main facets are -cut is very critical in determining the beauty of the finished stone. -The required angle at which these facets must be cut varies with the -refractive indices of the different varieties of gem minerals. If the -facets are not cut at exactly the proper angle, light entering the top -or crown of the gemstone can pass completely through the stone, instead -of being reflected back out of the crown facets. The result is a dull, -lifeless stone that appears to have a "hole" or "fish-eye" in the -center. Stones that are cut in this manner are greatly reduced in value. -The angle at which the facets are cut is controlled by the adjustment of -the height of the arm of the facet head on the post. The lapidary will -continually adjust this height, because the angle between the arm and -the surface of the lap changes slightly as the facet is ground down to -its proper place and size. - - [Illustration: Fig. 11. Proper sequence of cutting of the pavilion -facets. Left to right: four main facets; all eight main facets; half of - the pavilion girdle facets; completed pavilion.] - -The standard American brilliant cut will be used as an example of facet -cutting. Procedure for all other cuts is essentially the same to this -point. After the eight main pavilion facets have been cut, the cutting -angle is changed a few degrees, the arm of the facet head rotated -slightly, and the sixteen pavilion girdle facets or "skill" facets, as -they are often called, are cut (fig. 11). The pavilion girdle facets -should meet exactly in the center of the main facets at the girdle of -the stone. The pavilion girdle facets should neither overlap, nor should -there be any space between them (fig. 12). After the pavilion girdle -facets are cut, the cutting of the pavilion of the gemstone is -completed. The facets are then polished on the polishing lap at the same -angles and in the same order as they were cut, and the pavilion of the -gem is completely finished. - -The stone is then removed from the dop-stick by melting the dop-wax and -is re-dopped to the pavilion facets so that the crown of the stone is -now exposed for cutting. Before the lapidary proceeds with the cutting -of the crown, it is necessary that the stone be perfectly centered on -the dop-stick and that the plane of the table facet be perpendicular to -the dop-stick and to the axis of the arm of the facet head. The eight -main facets are cut first, with numerous adjustments being made by the -lapidary to insure that the proper angle is maintained (fig. 13). Then -the cutting angle is changed a few degrees, the arm of the facet head -rotated slightly, and the crown girdle facets are cut. The crown girdle -facets are placed very similarly to the pavilion girdle facets except -that they are shorter. The crown girdle facets should be joined in -exactly the same way as the pavilion girdle facets. When these facets -are properly cut, the cutting angle is again changed, the arm rotated, -and the eight star facets are cut. This completes the cutting of the -crown of the stone. The cutting lap is removed from the lap plate, and -the polishing lap is secured into place. The facets are carefully -polished in the same order that they were cut. After the last star facet -has been polished, the stone is removed from the dop-stick. Any excess -dop-wax is removed from the stone by means of a solvent, and the full -beauty of the finished gem is revealed. - - - - - Tumbled Gems - - -One other method of finishing gemstones that deserves mention is -tumbling. "Baroque" or "free-form" stones are produced in this manner. -Loose pebbles or pieces of gem materials left over from other cutting -processes are placed in a small barrel or specially constructed box with -loose carborundum grit. The barrel is turned by means of a small motor, -and the abrasion of the pebbles and grit against each other tends to -round the pebbles and give them a finely pitted surface. Progressively -finer and finer carborundum grit is used, and eventually a polishing -compound. The result is several pounds of well-polished gem pebbles of -various shapes and sizes. These baroque stones have found recent favor -in costume jewelry of modern design. The tumbling process is rather -slow, commonly requiring several days or weeks. However, little effort -is involved on the part of the lapidary, and, consequently, the cost of -most tumbled or baroque stones is quite modest. Only gem material that -is unsuitable for cutting in other manners should be finished in this -way. - - [Illustration: Fig. 12. Proper placing of the pavilion girdle facets. - Left: facets not joined. Center: facets overlapped, joined too high. - Right: correct placing.] - - Stone - Dop-wax - Dop-stick - Chuck - -[Illustration: Fig. 13. Proper sequence of cutting of the crown facets. - Left to right: four main facets; all eight main facets; half of the - crown girdle facets; completed crown.] - - - - - TEXAS GEMSTONES - - - - - Amber - - - _Composition_: fossil resin. _Crystal system_: amorphous. _Hardness_: - about 2.0 to 2.5. _Specific gravity_: variable, from 1.05 to 1.10. - _Luster_: resinous. _Color_: brown, yellow, red, orange, and white. - _Streak_: white to yellowish to gray. _Cleavage_: none. _Fracture_: - conchoidal. _Tenacity_: brittle. _Diaphaneity_: transparent to - translucent. _Refractive index_: variable, about 1.54. Burns with a - sweet, piney odor. - -Rich brown to yellowish amber has been found near Eagle Pass, Maverick -County, in Cretaceous coal and on Terlingua Creek, Brewster County. -Although much of this material is translucent and the quality suitable -for lapidary purposes, the pieces are seldom more than a fraction of an -inch in diameter. - -Occasional finds of poor quality brownish amber have been reported from -the Tertiary formations of the Gulf Coastal Plain, but thus far no gem -quality material has been found. - -The softness of amber limits its use to brooches, necklaces, and other -jewelry that is relatively safe from abrasion. - - - - - Augite - - - _Composition_: CaMgSi_2O_4; may also contain iron, aluminum, and - sometimes titanium. _Crystal system_: monoclinic. _Hardness_: 5 to 6. - _Specific gravity_: 3.2 to 3.6. _Luster_: vitreous to dull. _Color_: - dark greenish brown and greenish black. _Streak_: light grayish green. - _Cleavage_: two directions, poor. _Fracture_: conchoidal to uneven. - _Tenacity_: brittle. _Diaphaneity_: opaque to translucent. _Refractive - index_: variable, about 1.60 to 1.71. - -Augite of gem quality occurs near Eagle Flat, Hudspeth County, Texas. -Although this material is very dark greenish brown and not commonly -thought of as a gemstone, lapidaries have used it to fashion black -faceted stones and cabochons that resemble obsidian. Most of the augite -occurs as loose pieces and crystal fragments that have weathered out of -nearby igneous rocks; the augite can also be found in situ in the -igneous rocks. - -Specimens and pieces of cutting quality 1 inch in diameter are common, -and fragments over 2 inches in diameter have been found. The augite is -associated with black spinel and some dark gray to black pieces of -natural glass. Although the faceted and cabochon-cut stones are not -particularly attractive, some of the larger pieces of augite might be -utilized for carving. - - - - - Beryl - - - _Composition_: Be_3Al_2(SiO)_6. _Crystal system_: hexagonal. - _Hardness_: 7.5 to 8.0. _Specific gravity_: 2.63 to 2.80. _Luster_: - vitreous. _Color_: pale blue, blue, green, yellow, brownish, pink, and - colorless. _Streak_: white. _Cleavage_: one direction, very imperfect. - _Fracture_: conchoidal to uneven. _Tenacity_: brittle. _Diaphaneity_: - transparent to subtranslucent. _Refractive index_: 1.56 to 1.60. - _Dispersion_: low. - -Gem-quality beryl has not been reported in Texas. A discussion of beryl -is included herein because the writer believes it likely that beryl of -gem quality will be found in Texas as a result of future investigations -and exploration. - -Beryl crystals have been found in pegmatite dikes in Llano, Blanco, and -Gillespie counties. These crystals are commonly several inches long and -exceed 1 inch in diameter but are very badly fractured. Most of the -beryl crystals do not approach gem quality and are entirely unsuitable -for any lapidary use. The color of the crystals found thus far is -bluish, greenish, pinkish brown, yellowish, and colorless. Some very -tiny colorless beryl crystals have been found that are transparent, but -thus far such crystals have been too small to be cut into gems. - -Fine blue beryl crystals have been found in the Franklin Mountains near -El Paso, Texas. Unfortunately, these crystals are so badly flawed and -fractured that they are not suitable for lapidary use. - -It seems likely that careful prospecting of Texas pegmatites will reveal -at least some gem-quality beryl. - - - - - Celestite - - - _Composition_: SrSO_4. _Crystal system_: orthorhombic. _Hardness_: 3.0 - to 3.5. _Specific gravity_: 3.95 to 3.98. _Luster_: vitreous. _Color_: - white, blue, greenish, reddish, and brownish. _Streak_: white. - _Cleavage_: three directions, although one of these directions is not - easily developed. _Fracture_: uneven. _Tenacity_: brittle. - _Diaphaneity_: transparent to subtranslucent. _Refractive index_: 1.62 - to 1.63. _Dispersion_: moderate. - -Celestite is very seldom cut into gems. Being very soft, brittle, and -having three cleavages, celestite is completely unsuitable for jewelry. -These same properties make this mineral exceedingly difficult to facet; -however, faceted stones are seen in large collections. - -[Illustration: Fig. 14. Common crystal form of Travis County celestite. - Same crystal form as shown in Plate I, A.] - -Fine crystals of colorless and blue gem-quality celestite (Pl. I, A, and -fig. 14) have been found at Mount Bonnell and other localities west of -Austin, Travis County. The celestite crystals occur in vugs or geodes in -limestone. The crystals are mostly white or colorless and fractured near -the base or where attached, but the tips of the crystals are commonly -clear celestine blue and completely free of flaws. - -Crystals several inches in length have been found, but the average size -is about 1 inch. The smaller crystals are frequently more transparent -and consequently better suited for cutting. It is very difficult to -obtain crystals that will allow the cutting of flawless stones of more -than 4 or 5 carats. - -Bluish and colorless celestite of gem quality and fine crystals have -been found near Lampasas, Lampasas County, and near Brownwood, Brown -County, but neither of these localities has been very productive of good -gem material. - -Celestite geodes have been found in parts of Coke, Fisher, and Nolan -counties, but these geodes contain little gem material. - - - - - Diamond - - - _Composition_: carbon. _Crystal system_: isometric. _Hardness_: 10. - _Specific gravity_: 3.51 to 3.53. _Luster_: adamantine to greasy. - _Color_: brown, colorless, pink, blue, yellow, and various other light - colors; rarely deeply colored; sometimes black. _Cleavage_: four - directions, octahedral, perfect. _Fracture_: conchoidal. _Tenacity_: - brittle. _Diaphaneity_: transparent to opaque. _Refractive index_: - 2.42. _Dispersion_: high. - -There is only one well-authenticated find of diamond in Texas. A small -brownish diamond was found in 1911 on section 64, block 44, Foard County -(Sterrett, 1912, pp. 1040-1041). The exact weight of the stone has not -been recorded, but one authority estimated that it was of sufficient -size and clarity to yield a cut stone of about one-quarter carat. - -The only diamond-bearing rocks known in the United States are in Pike -County, Arkansas. Although many other diamonds have been found in the -United States, all were loose in gravels or streams except for some -stones at the Arkansas locality. The fact that one diamond was found in -Foard County does not mean that the prospects of finding more diamonds -in Texas are much better there than anywhere else in the State. It is -highly unlikely that more than a very few diamonds will ever be found in -Texas, and any stones that may be found in the future are likely to be -widely scattered. - - - - - Epidote - - - _Composition_: HCa_2(Al, Fe)_2Si_3O_1_3. _Crystal system_: monoclinic. - _Hardness_: 6 to 7. _Specific gravity_: 3.25 to 3.5. _Luster_: - vitreous. _Color_: yellowish green to brownish green and brown. - _Streak_: uncolored to grayish. _Cleavage_: two directions. - _Fracture_: uneven. _Tenacity_: brittle. _Diaphaneity_: transparent to - opaque. _Refractive index_: about 1.72 to 1.77. - -Llano County has furnished some green and brownish-green epidote that is -suitable for cutting into cabochons. Most of the material that -approaches gem quality has come from contact metamorphic zones and is -associated with garnet, quartz, and some scheelite. Some small cavities -in the rocks contain tiny transparent crystals of gem quality, but the -largest obtainable flawless faceted stones would probably be less than -15 points. - -Faceted stones of epidote are sometimes known as pistacite owing to -their common pistachio-green color. - - - - - Fluorite - - - _Composition_: CaF_2. _Crystal system_: isometric. _Hardness_: 4. - _Specific gravity_: 3.0 to 3.25. _Luster_: vitreous. _Color_: violet, - blue, colorless, green, yellow, brown, rose, and crimson red. - _Streak_: white. _Cleavage_: four directions, octahedral, perfect. - _Fracture_: subconchoidal to splintery. _Tenacity_: brittle. - _Diaphaneity_: transparent to subtranslucent. _Refractive index_: - 1.434. - -Very fine green, transparent fluorite has been found near Voca, Mason -County. The fluorite occurs as vug fillings in pegmatites, associated -with crystals of pink microcline and colorless quartz. Most of the vugs -have been completely filled by the fluorite; therefore, crystals (fig. -15) of the fluorite are not too common. Masses of fluorite several -pounds in weight, rich green, and quite transparent have been found near -Voca. Transparent pieces an inch or more in diameter are common. - - [Illustration: Fig. 15. Common crystal form of fluorite.] - -Fluorite is much too soft for everyday use in jewelry and because of the -low refractive index does not yield brilliant faceted stones. The -perfect four-directional cleavage, relative softness, and brittle -tenacity of the mineral make it difficult to facet. Faceted stones are -seldom seen outside of collections. Cabochons are also difficult to cut -from this material, but the rich color obtained is ample reward for the -time and care necessary in cutting. - -Fluorite occurs at several other localities in Texas, notably in -Hudspeth, Brewster, Presidio, Llano, and Burnet counties, but not -commonly in gem quality or colors that warrant its use as gem material. - - - - - Fossil Wood - - -Wood that is buried in silica-rich sediments is commonly replaced by -quartz, agate, or opal. The wood structure, including a large number of -the annular rings, knots, small branches, and bark, may be preserved. -This process of replacement by silica is believed to take considerable -time. Preservations by other means (_see_ Jet, p. 22) are known, but -silica replacements are most commonly used as gem materials. - -Fossil wood is often used by lapidaries as gem material when mineral -replacement preserves the wood structure sufficiently well and when -various impurities color the replacement material attractively. - -Excellent gem-quality fossil wood (Pl. I, B) has been found at a great -number of localities in Texas. Agatized and opalized wood occurs in -great abundance along the outcrops of Eocene and Oligocene strata of the -Texas Gulf Coastal Plain. Much of this material is very well suited for -cabochons, bookends, and other lapidary uses. The preservation is -especially good at numerous localities in Washington, Lee, Fayette, and -Gonzales counties, and the variety of colors, such as bluish, gray, -brown, red, yellow, and black, makes this material especially sought -after by "rock-hounds." Some of the agatized and opalized wood -fluoresces yellow or green under ultra-violet light. The fossil wood is -sometimes found as stumps, limb sections, or large trunk fragments, but -the great majority of the gem material is found as small broken -fragments or stream-rolled cobbles. - -Fossil palm wood is by far the most sought after variety because this -material displays "eyes" and tube-like structures that yield very -attractive cabochons and cabinet specimens. Texas fossil palm wood is -highly regarded by cutters from all parts of the country, and this -material is thought by many lapidaries to be some of the finest -gem-quality fossil wood in the United States. - -Gravel pits and river gravels in Live Oak County have produced very fine -agatized wood. Although the gem material does not seem to be as abundant -in this area as it is in counties to the northeast, the vivid colors and -excellent preservation of the fossil wood in Live Oak County have -attracted collectors from all over the State. The fossil wood usually -occurs as large rounded cobbles in the streams. Much of this material is -quite translucent when cut and contains various shades of brown, orange, -and red. - -The gravels of the Rio Grande have produced some fossil wood in addition -to the excellent agate that is also found there. Most of the fossil wood -found in these gravels is very well preserved, but the colors are -commonly dull shades of brown. Occasional fine red and yellow specimens -have been recovered from the Rio Grande gravels, but these are rare. - -Good agatized wood has been found in and near Palo Duro Canyon, -Armstrong County, about 50 miles southeast of Amarillo. Large trunk -sections are not uncommon, but most of the material of cutting quality -is obtained from small fragments. The Palo Duro Canyon fossil wood -greatly resembles the famous Arizona Petrified Forest wood but is not -nearly as plentiful. The Palo Duro wood contains yellow, brown, red, and -bluish colors most commonly. Some of the wood-producing area is within -Palo Duro Canyon State Park which is, of course, closed to collecting. -The surrounding area has been worked diligently by local collectors, but -new pieces of wood are exposed after heavy rains. - -Webb and Duval counties have also produced some good fossil wood -specimens. - - - - - Gadolinite - - - _Composition_: Be_2FeY_2Si_2O_1_0. (Various other rare-earth elements - may substitute into this mineral structure.) _Crystal system_: - monoclinic. _Hardness_: 6.5 to 7.0. _Specific gravity_: about 4.2. - _Luster_: vitreous to greasy. _Color_: black; in thin splinters dark - bottle green. _Streak_: white to greenish. _Cleavage_: none. - _Fracture_: conchoidal to splintery. _Tenacity_: brittle. - _Diaphaneity_: opaque to subtransparent in thin pieces. _Refractive - index_: variable, about 1.77 to 1.82. - -Gadolinite as a cut gem is not seen outside of large collections; -however, it can be faceted into black opaque stones of little beauty but -of great interest to collectors. The best known locality of this mineral -in the United States is Baringer Hill, Llano County, Texas. -Unfortunately, this locality was completely flooded by the completion of -Buchanan Dam in 1938. Masses and rough crystals of gadolinite weighing -over 100 pounds were mined from this locality. The gadolinite occurred -in a large, very coarse-grained pegmatite dike associated with quartz, -microcline, and fluorite, as well as allanite, fergusonite, nivenite, -cyrtolite, thorogummite, and various other rare minerals. Some of the -minerals in the dike occurred in very large masses. One quartz mass over -40 feet in diameter was noted, and microcline masses up to 30 feet in -diameter were not uncommon. Much of the gadolinite was used by -industrial firms as a source of thorium compounds, although some -specimen and gem material found its way into museums and private -collections. Because the locality was worked mostly from 1910 to about -1925 and because since 1938 the waters of Lake Buchanan have completely -flooded the entire area, material from this locality is now exceedingly -difficult to obtain. The collection of the Smithsonian Institution, -Washington, D.C., contains a cut and polished gem of Baringer Hill -gadolinite that weighs 8.6 carats. This mineral is radioactive because -of the presence of uranium, thorium, and other rare radioactive -elements. - - - - - Garnet - - -The garnet group of minerals is variable in composition. Listed below -are the pure members of this group, but garnets found in nature are -usually a mixture of two or more of these end members. - - Aluminum garnet-- - Grossularite (calcium-aluminum garnet), Ca_3Al_2(SiO_4)_3 - Pyrope (magnesium-aluminum garnet), Mg_3Al_2(SiO_4)_3 - Almandite (iron-aluminum garnet), Fe_3Al_2(SiO_4)_3 - Spessartite (manganese-aluminum garnet), Mn_3Al_2(SiO_4)_3 - Iron garnet-- - Andradite (calcium-iron garnet), Ca_3Fe_2(SiO_4)_3; may contain - magnesium, titanium, and yttrium - Chromium garnet-- - Uvarovite (calcium-chromium garnet), Ca_3Cr_2(SiO_4)_3 - -Since almandite is the only variety of garnet known to occur commonly in -gem quality in Texas, the following properties are for almandite except -where noted. - - _Crystal system_: isometric (all varieties). _Hardness_: about 7.5. - _Specific gravity_: 4.25. _Luster_: vitreous to resinous. _Color_: - red, deep red, and brownish red (other varieties also yellow, white, - orange, pink, black, and green). _Streak_: white. _Cleavage_: none. - _Fracture_: subconchoidal to uneven. _Tenacity_: brittle to tough. - _Diaphaneity_: transparent to subtranslucent. _Refractive index_: - about 1.83. - -Good crystals of gem-quality almandite garnet have been found in Llano, -Blanco, Burnet, and Gillespie counties. In southeast Llano County, -northwest Blanco County, and northeast Gillespie County, the stones -mostly occur in stream gravels where they have collected after being -weathered out of compact mica schists. Owing to the fact that most of -the garnets have not been transported very far from their source, the -stones commonly show good crystal form (Pl. II, A). All of the garnets -from one locality commonly do not have exactly the same crystal form. -The garnets are mostly widely scattered in the stream gravels but can be -found concentrated behind rocks and on small gravel bars. - -Many of the crystals are less than one-eighth inch in diameter; however, -good crystals one-fourth to one-half inch in diameter are common. Most -of the stones are too fractured or have too many inclusions to yield -gems, but many transparent stones have been found. The transparent -crystals usually yield flawless deep red faceted stones of 2 carats or -less. Some of the stones that contain too many inclusions to facet are -cut as cabochons and are then often known as carbuncle. - -Small garnet fragments have been found in streams and in gneisses and -pegmatites near Castell, Llano County, but they are not commonly of gem -quality. - -Occasional small gem-quality garnets have been found in pegmatites and -contact metamorphic zones in Burnet County. Garnets have also been found -in several other counties, notably Mason, El Paso, Hudspeth, and -Culberson, but no stones of facet quality have been reported. - - - - - Jet - - - _Composition_: a variety of brown coal or lignite. _Structure_: woody. - _Hardness_: 3 to 4. _Specific gravity_: about 1.30 to 1.35. _Luster_: - dull. _Color_: black, brownish black. _Streak_: brown to brownish - black. _Cleavage_: none. _Fracture_: uneven to smooth. _Tenacity_: - tough to slightly brittle. _Diaphaneity_: opaque. Burns with a sooty - yellowish flame. - -Jet is a type of fossil wood in which there has been sufficient chemical -change to make the wood relatively hard and black without destroying the -woody structure. The best specimens of jet polish into lustrous black -cabochons. - -Jet occurs in Presidio County as compressed and flattened trunks of -trees in a thin layer of coal and lignite in Cretaceous strata 100 to -200 feet stratigraphically below the San Carlos beds. - -Specimens of "jet" have been found in some of the lignitic Tertiary -strata of the Texas Gulf Coastal Plain; however, this material is mostly -soft, brownish, and not of gem quality. - - - - - Labradorite - - - _Composition_: NaAlSi_3O_8, 50% to 30%; CaAl_2Si_2O_8, 50% to 70%. - _Crystal system_: triclinic. _Hardness_: 6.0 to 6.5. _Specific - gravity_: about 2.60. _Luster_: vitreous to sometimes pearly. _Color_: - straw yellow, white, greenish, gray, reddish, bluish, and green. - Sometimes shows a play of colors on particular cleavage surfaces. - _Streak_: uncolored. _Cleavage_: three directions. _Fracture_: uneven - to conchoidal. _Tenacity_: brittle. _Diaphaneity_: transparent to - translucent. _Refractive index_: about 1.56. _Dispersion_: low. - -Very fine facet-quality labradorite has been found about 20 miles south -of Alpine, Brewster County. The labradorite occurs loose in the soil as -slightly weathered or frosted cleavage fragments, commonly showing one -or more crystal faces (Pl. II, B). The pale-yellow or straw-yellow color -of these fragments, as well as their lack of internal imperfections, -makes these stones excellent gem material. Individual pieces that exceed -three-fourths inch in their longest dimensions are rare. Cut stones of -more than 5 or 6 carats from this locality are scarce. The source of -this material is uncertain, but it is probably weathering out of an -underlying igneous rock. - - - - - Microcline - - - _Composition_: KAlSi_3O_8. _Crystal system_: triclinic. _Hardness_: - 6.0 to 6.5. _Specific gravity_: 2.54 to 2.57. _Luster_: vitreous to - pearly. _Color_: white, pale yellow, red, blue green, bluish. - _Streak_: white. _Cleavage_: four directions, usually three of these - distinct. _Fracture_: uneven. _Tenacity_: brittle _Diaphaneity_: - transparent to translucent. _Refractive index_: about 1.52 to 1.53. - -Very fine crystals of blue microcline have been found east of Packsaddle -Mountain and near Kingsland in Llano County. Crystals exceeding 1 foot -in length have been found, although most are only a few inches long. The -color of the microcline is mostly pale blue, but some crystals are -darker. Microcline crystals associated with milky or vein quartz, smoky -quartz, some biotite, and rarely cassiterite occur in pegmatite dikes -which vary in size from a few inches to several feet in thickness. The -color of this microcline is pale in comparison to microcline from some -other localities in the United States, but the Texas blue microcline -does yield pleasing cabochons. Perfect crystals of this material are -prized by collectors. Blue or greenish microcline is often called -amazonite or amazon stone. - -Bluish microcline associated with quartz and topaz has also been -reported near Katemcy, Mason County. - -Red microcline is common in several central Texas counties and is a -primary constituent of many of the igneous rocks in those counties. -Large crystals of perthitic red microcline occur in pegmatite dikes of -Mason, Llano, Burnet, and Gillespie counties. Any feldspar quarry or -other pegmatite mining operation in any of these counties is likely to -contain large red microcline crystals and fragments. Unfortunately, the -good crystals that may have been present are often shattered by blasting -during quarrying operations. - -Feldspar quarries in northeastern Gillespie County have yielded some -good red cabochon material as well as good crystals. Here the microcline -occurs with milky and smoky vein quartz, smoky quartz crystals, clear -quartz crystals, greenish muscovite, and biotite. Many of the older -quarries in Gillespie County have not been active for some time, and the -dumps and quarry walls have been diligently searched by collectors. - - [Illustration: Fig. 16. Crystal faces on microcline specimen shown in - Plate III, A.] - -Many of the pegmatite dikes near Lake Buchanan in Llano and Burnet -counties have produced some good red microcline specimens and cutting -material (Pl. III, A, and fig. 16). Many of these crystals are more -pinkish than those in Gillespie County, but this is commonly due to the -fact that the crystal faces of the Lake Buchanan area crystals are -somewhat more weathered than the fresh Gillespie County crystals. - -Numerous other local areas in the counties mentioned, as well as some -localities in Hudspeth and Culberson counties, have also produced small -amounts of red and pink microcline of gem quality. - - - - - Obsidian - - - _Composition_: volcanic glass. _Structure_: amorphous. _Hardness_: 5.0 - to 5.5. _Specific gravity_: 2.3 to 2.5. _Luster_: vitreous. _Color_: - black, dark gray, reddish, brown, bluish, and greenish. _Streak_: - white. _Cleavage_: none. _Fracture_: conchoidal. _Tenacity_: brittle. - _Diaphaneity_: translucent to nearly opaque. _Refractive index_: - variable, about 1.45 to 1.53. - -Gem-quality black and dark-gray obsidian has been found in Presidio -County associated with extrusive igneous rocks. The obsidian in this -area is too opaque to serve as attractive faceted stones but is found in -pieces of sufficient size and quality to yield nice cabochons. Some of -the small weathered pieces of this material resemble tektite in outward -appearance; in fact, the "valverdites" mistaken originally for tektites -are pebbles of weathered obsidian in terrace gravel of Val Verde County. -Obsidian takes a high polish but is very sensitive to heat. Stones that -are slightly overheated during grinding or sanding will quickly shatter. - -Obsidian of gem quality has been reported also in Brewster County. - - - - - Opal - - - _Composition_: SiO_2·nH_2O. _Structure_: amorphous. _Hardness_: 5.5 to - 6.5. _Specific gravity_: 1.9 to 2.3. _Luster_: subvitreous to pearly. - _Color_: white, bluish, pink, brown, yellow, and gray. _Streak_: - white. _Cleavage_: none. _Fracture_: conchoidal. _Tenacity_: brittle. - _Diaphaneity_: transparent to nearly opaque. _Refractive index_: 1.43. - -Opal other than as fossil or opalized wood (pp. 20-21) occurs at the -following several localities in Texas. - -Approximately 16 miles south of Alpine, Brewster County, precious opal -occurs in very small seams and as cavity fillings in very hard -pinkish-brown rhyolite. This opal is milky or bluish and commonly -exhibits small flashes of blue, green, red, and orange fire. Individual -pieces of this opal are mostly quite small, rarely over one-fourth inch -in diameter, and very difficult to remove from the tough rhyolite -matrix. Local lapidaries have cut interesting cabochons from this -material in which several small patches of opal that are close together -in the matrix are included in the same cabochon. - -Small finds of opal associated with rhyolites and basalts have come from -other localities in west Texas, but the opal mostly does not display -enough play of colors to warrant its use as gem material. - -Near Freer, Duval County, some very attractive common opal has been -found. The opal is colored various shades of pink, blue, and yellow and -in certain local areas occurs as fragments that are cemented together by -clear chalcedony. Various colors are commonly found in the same piece, -and such material yields handsome cabochons. Although the area has never -been worked commercially, it has been hunted by collectors and cutters -for several years. - - - - - Pearl - - -Pearls are the result of the secretion of calcium carbonate by various -shellfish around sand grains, parasitic organisms, shell fragments, or -other foreign objects that have in some way entered the body cavity of -the shellfish. Since the shellfish is unable to expel these irritating -particles or organisms, it deposits successive layers of calcium -carbonate around the foreign substance to make it smoother and less -irritating. Although pearls are principally calcium carbonate, they also -contain small amounts of an organic substance, called conchiolin, and -water. Pearls are found in shellfish that live in either fresh or salt -water. Few pearls are spherical in shape; most are rounded but somewhat -irregular and are known as baroque pearls. Good quality pearls are the -only gemstone commonly sold by the grain, a unit of weight equal to 0.25 -carat or 0.05 gram. The pearl grain is not the same unit of weight as -the Troy grain. - -In Texas, pearls have been found in fresh-water clams in most of the -major rivers and streams, notably in the Brazos, Concho, Colorado, -Guadalupe, Llano, Nueces, Sabine, Rio Grande, and Trinity Rivers. -Several Texas lakes have also yielded pearls, notably Caddo Lake and -other lakes in north-central and northeast Texas. - -Small pearls are frequently found along the Texas Gulf Coast in edible -oysters and other common shellfish. Fossil pearls have also been found -but because of their darkened appearance are of value only as -curiosities. - -The pearls thus far found in Texas have been of relatively poor quality -and show little or no iridescence. These pearls have little value except -as curiosities, although one writer has stated that the discovery of -pearls in the Nueces River led to the original Spanish settlement of the -State (Baker, 1935, p. 569). - - - - - Quartz - - - _Composition_: SiO_2. _Crystal system_: hexagonal. _Hardness_: 7. - _Specific gravity_: 2.65 to 2.66 in crystals. _Luster_: vitreous, also - waxy, greasy, and dull. _Color_: most often colorless, brown, yellow, - violet; sometimes green, red, blue, and black; cryptocrystalline - varieties often variously colored by impurities. _Streak_: white. - _Cleavage_: indistinct. _Fracture_: conchoidal to splintery. - _Tenacity_: brittle to tough. _Diaphaneity_: transparent to opaque. - _Refractive index_: 1.544 to 1.553. - -The quartz family gemstones can be divided into two groups for purposes -of description. The first group is the crystalline varieties, or those -quartz varieties that commonly occur in distinct crystals. The second -group is the cryptocrystalline varieties, or those quartz varieties that -occur as irregular masses that are composed of many microscopic -crystals. The crystalline varieties are usually much more transparent -and are most often seen as faceted stones. The cryptocrystalline -varieties vary from subtransparent to opaque and are almost always cut -as cabochons. - - - - - CRYSTALLINE VARIETIES - - -_Amethyst_ (violet to purple-colored quartz).--A northeastern Gillespie -County locality known as Amethyst Hill has produced quite a number of -fine light to medium violet amethyst crystals which occur in quartz -veins and geodes associated with serpentine and talc. Many crystals have -been found loose in the soil. - -The amethyst tends to be very irregularly colored in zones parallel to -the crystal faces. In many, the base of the crystal is colorless or -white and only the termination is violet. Crystals up to 3 inches long -have been found at this locality, but the average size is much less. - -The surface at this locality is almost entirely depleted of amethyst, -with only an occasional small crystal or fragment to be seen. However, -small excavations are still sometimes productive. - -Good groups of pale amethyst crystals have been found in quartz veins -near the old town site of Oxford, Llano County. The occurrence seems to -be much the same as the Amethyst Hill locality. Little exploration for -gemstones has been done in this area, and future discoveries seem -likely. - -Chalcedony geodes lined with amethyst crystals have been found in -Brewster, Presidio, Culberson, and Hudspeth counties, but the -occurrences are scattered. The crystals are seldom large enough to yield -gems of more than 3 carats and are mostly very light colored. - -A few pieces of gem-quality amethyst have been found in Burnet County. - -_Citrine_ (yellow quartz).--Very little gem-quality citrine has been -reported in Texas. Some small citrine crystals have been found at -Amethyst Hill in northeastern Gillespie County, but few are of -sufficient size or color to yield good gems. - -The writer has seen one citrine crystal that was found in the gravels of -a small stream in eastern Llano County near Buchanan Dam. The crystal -weighs about 1 ounce and is perfectly clear, light golden yellow, and -flawless. However, a further search of the stream gravels failed to -produce any other citrines. - -_Rock crystal_ (colorless quartz).--Numerous localities in Texas produce -this colorless variety of quartz, which is the most common variety of -facet quality quartz and consequently is of little value. - -Rock crystal occurs at many localities in Burnet, Llano, and Mason -counties. The crystals mostly occur in pegmatite dikes or in stream -gravels where they have been weathered out of their parent rock. Some -fine colorless quartz crystals have been found near Voca, Mason County, -in weathered pegmatite dikes and also loose in the sands of nearby -streams. Crystals from this locality are often stained with reddish iron -oxide on their outer surfaces. Some of the rock crystal found near -Katemcy, Mason County, shows asterism when cut with the proper -orientation. Fine clear colorless crystals up to 8 inches long have been -found in the pegmatite dikes near Lake Buchanan in both Llano and Burnet -counties. Several localities near Enchanted Rock in Llano County have -also produced some good colorless crystals. - -Feldspar quarries in large pegmatites in northeastern Gillespie County -have yielded attractive quartz crystals, some of which contain smoky -phantom crystals and tourmaline inclusions. - -Some pieces of rock crystal enclosing green, needle-like actinolite -crystals have been found near the Llano-Gillespie-Blanco County corner. -This material is not suitable for faceted gems but does lend itself to -interesting and attractive cabochons. - -Colorless quartz crystals commonly are found lining small chalcedony -geodes in Brewster, Presidio, Culberson, Hudspeth, Reeves, and Jeff -Davis counties. These crystals are most commonly less than 1 inch long -but are mostly very clear. - -Rock crystal has been found in crevices of petrified wood in many east -and southeast Texas counties, although the crystals are mostly quite -small. - -Many lesser occurrences of rock crystal, too numerous to mention, are -located within the State. - -_Rose quartz_ (pink quartz).--Rose quartz occurs at various localities -in Burnet, Llano, Mason, and Gillespie counties, but the amount of -material is mostly small and the greater part unsuitable for gem -purposes. Some good pink rose quartz occurs near Town Mountain, Llano -County, but this material does not have flawless areas large enough to -yield faceted stones of more than a few carats. Rose quartz is always -slightly milky, or cloudy, and does not cut into brilliant faceted -stones. The Town Mountain rose quartz has been cut into attractive -cabochons. - -_Smoky quartz_ (brown, yellow-brown, and golden-brown quartz).--Several -Texas localities have produced fine smoky quartz. Baringer Hill, a noted -rare-earth minerals pegmatite locality in Llano County, contained some -smoky quartz crystals that were estimated to weigh over 1,000 pounds, -and the locality produced many smaller crystals that were of gem -quality. Baringer Hill was flooded by the completion of Buchanan Dam in -1938 and is presently under the waters of Lake Buchanan. A few fine -golden-brown gem-quality crystals have been found along the lake shore -and in small pegmatites nearby (Pl. III, B.). - -Feldspar quarries in northeastern Gillespie County have produced smoky -quartz crystals that exceed 1 foot in length, but these crystals are -mostly flawed, possibly as a result of blasting, and mostly contain only -small clear areas. - -Good color smoky quartz crystals are found with topaz in the pegmatites -and stream beds in Mason County, near Streeter, Grit, and Katemcy. These -crystals tend to be lighter colored than those near Lake Buchanan, but -they commonly contain large flawless areas. - - - - - CRYPTOCRYSTALLINE VARIETIES - - -_Chalcedony._--When free from impurities of various oxides and other -compounds, chalcedony has little to render it pleasing as a gemstone. It -is mostly gray, white, brown, or bluish and commonly has a waxy luster. -Some of the chalcedony found along the Rio Grande Valley and in west -Texas will take dyes, and local lapidaries have had some success in -dyeing this material various shades of blue, green, yellow, and red. -When the chalcedony is naturally colored and variegated, usually in -bands, mossy figures, or dendritic forms, it is called agate. - -_Agate_ (variegated chalcedony).--The wide variety of markings and -colors available together with the ease of cutting make agate a favorite -of many lapidaries. Fine agate has been found at numerous localities in -west and south Texas. Fine plume agate, famous throughout the United -States, is found south of Alpine. Plume agate is characterized by -dendritic or tree-like inclusions and is mostly cut into very handsome -cabochons. The agate from south of Alpine commonly contains black, red, -yellow, or brown plumes within the same piece. The variety of colors and -lack of porosity of this agate make it highly desired among lapidaries. -The agate occurs loose on the surface of the ground and in the soil in -small nodules that have a very rough, brownish surface. These nodules -are mostly less than 3 inches in diameter, although specimens of gem -quality have been found that exceed 200 pounds. - -Some very fine agate has been found in the vicinity of Needle Peak, -Presidio County. This material is mostly green moss agate in clear -chalcedony and commonly contains small yellow "sun-burst" figures. The -contrasting yellow and green design makes very beautiful cabochons. - -Fine agate has been found south of Marfa, Presidio County. This agate is -mostly clear chalcedony with black, yellow, or variously colored plumes, -moss, or "bouquet-like" figures. - -Numerous other localities in Presidio and Brewster counties have -produced good agate. - -Various amounts of agate, jasper, and chalcedony occur in the gravels of -the Rio Grande in varying quantities from Big Bend National Park -downstream to Brownsville. This agate is found both in the present river -gravels and in the older river gravels that now are located on nearby -hills and slopes up to several miles north or south of the present Rio -Grande. The greatest concentration of agate and related gem materials -seems to be in the area between Laredo and Rio Grande City. Vast -quantities of excellent gem material have been removed from this area -for many years (Pl. IV). The agate occurs as rounded, stream-worn -cobbles and commonly has a thin white coating that makes it difficult to -distinguish from the abundant chert and other rocks. The agate occurs in -cobbles that are mostly 3 to 6 inches in diameter, but specimens of gem -quality that exceed twice this size are known. The agate varies greatly -in design and color. Plume, moss, banded, and sagenitic agate occur in -these gravels in a wide variety of colors. The jasper in the Rio Grande -gravels is yellow, red, green, or various shades of these and is -commonly suspended as angular fragments in clear chalcedony. - -Good agate has also been found near Balmorhea in Reeves and Jeff Davis -counties and in smaller amounts at numerous other west and south Texas -localities. - -_Agatized wood_ (_see_ Fossil wood, pp. 20-21). - -_Carnelian_ (translucent reddish chalcedony).--This variety of -chalcedony in small quantities has been reported from near Van Horn, -Hudspeth County. Small pieces of carnelian have been found in the -gravels of the Rio Grande, but finds have been few and scattered. - -_Jasper_ (impure opaque or subtranslucent quartz).--Good green, yellow, -red, and brown jasper has been found in the gravels of the Rio Grande at -all of the localities that produce agate. The colors are quite vivid, -and the material takes a fine polish. Some pieces of orbicular jasper -(jasper with circular or eye-like markings) have been found in this -material. These gravels commonly contain jasper as fragments that are -suspended in clear chalcedony; this is called brecciated jasper and -yields very handsome cabochons. - -Many of the west Texas agate localities also produce jasper in quantity. -Good jasper has been reported from north of Brackettville, Kinney -County. Jasper is a minor constituent of the stream gravels in many -parts of the State. - - - - - Sanidine - - - _Composition_: KAlSi_3O_8; commonly contains some sodium. _Crystal - system_: monoclinic. _Hardness_: 6. _Specific gravity_: 2.57 to 2.58. - _Luster_: vitreous to pearly. _Color_: colorless, white, pale yellow, - and gray. _Streak_: uncolored. _Cleavage_: three directions. - _Fracture_: conchoidal to uneven. _Tenacity_: brittle. _Diaphaneity_: - transparent to subtranslucent. _Refractive index_: 1.52 to 1.53. - -Some feldspars, including sanidine, show a nice blue sheen in reflected -light parallel to certain crystallographic directions. Stones having -this property are called moonstone. A clear yellowish sanidine showing -an attractive blue sheen has been found in Brewster, Jeff Davis, and -Presidio counties. The individual pieces are small, the average size -being about one-eighth inch. The sanidine is found loose in the soil at -some localities where it has weathered out of rhyolite, and specimens of -the sanidine in the parent rock are not difficult to obtain. Very small -cabochons can be cut from this material, but few lapidaries have done so -because inexpensive larger pieces of moonstone can be obtained easily -from foreign sources. However, the west Texas sanidine does show a blue -sheen when cut and polished. - - - - - Spinel - - - _Composition_: MgAl_2O_4 (magnesium may be replaced in part by ferrous - iron or manganese and the aluminum by ferric iron and chromium). - _Crystal system_: isometric. _Hardness_: 8. _Specific gravity_: 3.5 to - 4.1. _Luster_: vitreous to sub-metallic. _Color_: black, pink, red, - blue, green, yellow, brown, and violet. _Streak_: white. _Cleavage_: - one direction, imperfect. _Fracture_: conchoidal. _Tenacity_: brittle. - _Diaphaneity_: transparent to opaque. _Refractive index_: variable, - approximately 1.72 to 2.00. - -In many areas of the world, fine quality, beautifully colored, -transparent spinels are found and used as gems. The only gem-quality -spinel reported thus far in Texas is black and opaque. Near Eagle Flat -in Hudspeth County, black spinel crystals have been found associated -with augite and natural glass; these minerals are weathering out of an -intrusive igneous rock. The spinel crystals have an octahedral form -which is common for this mineral (fig. 17). Most of the spinels are free -of flaws, but because of their black color they have little value as -gems. The crystals are found loose in the sand of streams near the -outcrops of the igneous rock or embedded in the rock. They seldom exceed -half an inch in diameter. These stones are primarily sought by -collectors. - - [Illustration: Fig. 17. Common crystal form of spinel.] - - - - - Tektite (Bediasite) - - - _Composition_: A natural glass, approximately 75% SiO_2, 15% Al_2O_3, - 4% FeO, also MgO, Na_2O, K_2O, and traces of other elements. _Crystal - structure_: amorphous. _Hardness_: 5 to 6. _Specific gravity_: 2.33 to - 2.44. _Luster_: vitreous, often dull on weathered surfaces. _Color_: - dark brown, greenish brown, appears black in thick sections. _Streak_: - uncolored. _Cleavage_: none. _Fracture_: conchoidal. _Tenacity_: - brittle. _Diaphaneity_: transparent to subtransparent. _Refractive - index_: 1.488 to 1.512. - -The average bediasite size is about 1 inch in diameter, although -specimens approximately 3 inches in diameter are known. The uncut -tektites are very interesting, showing a variety of shapes and surface -features (Pl. V, A) and many exhibit contorted flow structure. The -surface of many tektites is grooved or furrowed, while on others it is -smooth or frosted. The Texas tektites are known as "bediasites," after -place names in Grimes County traceable to the Bedias Indians who -formerly lived there. - -Dark brown and greenish-brown tektites have been found in Texas in -gravels at scattered localities in Walker, Grimes, Brazos, Burleson, -Lee, Fayette, Gonzales, Lavaca, and DeWitt counties. Outside of Texas -the only other authenticated tektite localities in the United States at -the present time are in Dodge and Irwin counties, Georgia. A fragment of -a similar tektite has recently been reported from near Martha's -Vineyard, Massachusetts. The tektites reported from Oklahoma are now -known to be pebbles of obsidian. - -Although tektites have little value or beauty as gemstones, they have -been cut by lapidaries as both faceted and cabochon stones. Tektites -take a high polish but are mostly so dark in color that they appear -black. - -The origin of tektites is of great scientific interest and is currently -the subject of much debate. Some scientists believe that tektites are of -meteoritic origin, while others believe that tektites were formed by -various terrestrial processes. Since no one has actually observed a -tektite to fall or form, and many of the theories of origin are -difficult to prove without direct observation, the origin of tektites is -likely to remain in controversy for some time. - - - - - Topaz - - - _Composition_: Al_2(F, OH)_2SiO_4. _Crystal system_: orthorhombic. - _Hardness_: 8. _Specific gravity_: 3.4 to 3.6. _Luster_: vitreous. - _Color_: pale blue, sky blue, greenish, white, wine yellow, straw - yellow, grayish, pink, reddish, and orange. _Streak_: uncolored. - _Cleavage_: one direction, basal, highly perfect. _Fracture_: - conchoidal to uneven. _Tenacity_: brittle. _Diaphaneity_: transparent - to subtranslucent. _Refractive index_: about 1.60 to 1.63. - _Dispersion_: moderate. - -Various yellow and smoky colored quartz gems are offered for sale as -"Spanish Topaz," "Smoky Topaz," "Madeira Topaz," and "Topaz Quartz." -These names are entirely misleading and should be dropped from usage. - -Fine gem-quality white, pale-blue, and sky-blue topaz has been found -near Streeter, Grit, and Katemcy, Mason County. This Texas gem material -compares favorably in color, size, and clarity with topaz found anywhere -in the United States. Fine crystals of topaz (Pl. V, B, and fig. 18) -occasionally are found in pegmatite dikes associated with quartz, black -tourmaline, cassiterite, and pink microcline. Many of the gem-bearing -pegmatites have been eroded away, leaving the topaz concentrated in the -stream beds. The stones mostly occur as frosted, stream-worn pebbles -(Pl. VI, A) in the numerous small creeks in the area. The topaz is -heavier than the quartz and microcline that compose the stream gravel -and is commonly found immediately on top of the granite bed-rock in the -bottom of the stream bed. The stones tend to lodge behind boulders or -small dikes cutting across the stream. - - [Illustration: Fig. 18. Crystal faces on topaz crystal shown in Plate - V, B. This crystal habit is typical of the topaz from Mason County.] - -The white or colorless stones are by far the most common, outnumbering -the bluish stones about ten to one. The color of the blue stones tends -to be irregularly distributed in zones parallel to the crystal faces. -Topaz that is colored in this manner should be cut with the best blue -color near the bottom or culet of the gem (fig. 19). If done correctly, -this will give the entire gemstone the desirable blue color. - -[Illustration: Fig. 19. Cross section showing the proper orientation of - dark-color zone in a gem cut from an irregularly colored stone.] - - COLORLESS - BLUE - -The colorless stones can be turned pale yellow, yellowish brown, or -straw yellow by exposure to X-ray radiation, and some of the bluish -stones will fluoresce faintly yellowish under ultra-violet light. - -The largest gem-quality topaz crystal yet found in North America has -come from Mason County. It is a pale-blue crystal weighing 1,296 grams, -now in the collection of the U.S. National Museum. Several other large -pieces, some weighing over a pound, have been found. One large crystal, -exact weight unknown, was found near Katemcy. Several gem cutters have -estimated that this stone could easily yield a single, flawless -pale-blue gem of about 500 carats. Many large gems have been cut from -topaz found in this area, including at least one stone of over 300 -carats. - -One obstacle in the cutting of topaz is its perfect basal cleavage. The -gemstone should be oriented so that no facet of the stone will be -parallel to or within less than about 5 degrees of the cleavage -direction, or the facet may be very difficult or impossible to polish. - -It is difficult to estimate the productivity of this area since its -discovery in the early 1900's. Few systematic attempts have been made to -exploit the deposits, and a great amount of the topaz thus far recovered -has been found by private collectors. The Mason County topaz deposits -are still very productive, and additional exploration may uncover even -more gem-producing areas. - -Topaz has also been found in stream gravels or pegmatites in Burnet, -Llano, Gillespie, and El Paso counties but very rarely in gem quality. - - - - - Tourmaline - - - _Composition_: H_9Al_3(B·OH)_2Si_4O_1_9; hydrogen often replaced by - iron, magnesium, calcium, or fluorine. _Crystal system_: hexagonal. - _Hardness_: 7 to 7.5. _Specific gravity_: 2.98 to 3.20. _Luster_: - vitreous to resinous. _Color_: black, brownish black, brown, blue, - green, red, pink, yellow, and gray. _Streak_: uncolored. _Cleavage_: - two directions, very imperfect. _Fracture_: subconchoidal to uneven. - _Tenacity_: brittle. _Diaphaneity_: transparent to opaque. _Refractive - index_: about 1.62 to 1.64. - -Black tourmaline is schorl; brown tourmaline, dravite. - -Good crystals of black and dark brown tourmaline occur at Town Mountain -near Llano, Llano County. The tourmaline crystals average about 1 inch -in length, do not commonly exceed 2 inches, and are associated with -white vein quartz. The quartz completely encloses the tourmaline, but -the crystals can be broken free or the quartz can be trimmed away with -the use of a diamond saw. The latter procedure is recommended whenever -possible, for it is very easy to shatter the tourmaline crystals while -trying to remove them from the quartz by other means. Many of the -crystals are completely unsuitable for cutting, being too brittle or too -badly cracked and flawed. However, some small crystals have been found -that are of sufficient quality and size to yield flawless stones of a -few carats. Few of these stones have been cut since the tourmaline is so -dark that it appears opaque, and few persons find a gem of this nature -attractive. - -Good black and dark brown crystals of tourmaline associated with -andalusite and graphite occur in the Packsaddle schist (Precambrian) -near Sunrise Beach, Llano County (Pl. VI, B, and fig. 20). Although -generally smaller in diameter than the crystals found at Town Mountain, -they commonly exceed 3 inches in length, although the average size is a -little over 1 inch. Many of these crystals are suitable for cutting into -opaque or nearly opaque stones of about 5 or 6 carats. - -Black tourmaline has also been found in Hudspeth and Culberson counties -but not of sufficient quality to be used as a gemstone. - -[Illustration: Fig. 20. Common crystal form of Llano County tourmaline.] - - - - - Turquoise - - - _Composition_: hydrous phosphate of aluminum and copper. _Crystal - system_: triclinic. _Hardness_: 5 to 6. _Specific gravity_: variable, - 2.6 to about 2.8. _Luster_: dull, sometimes waxy. _Color_: sky blue to - greenish blue. _Streak_: white to greenish. _Cleavage_: none in - massive material, two directions in crystals. _Fracture_: conchoidal - to subconchoidal. _Tenacity_: brittle. _Diaphaneity_: subtranslucent - to opaque. _Refractive index_: 1.61 to 1.65. - -Turquoise of good sky-blue to greenish-blue color has been found a few -miles southwest of Van Horn, Culberson County. Several shallow pits were -dug at this locality about 1910; however, the amount of turquoise -produced was small. The main occurrence of the turquoise was in seams -about 1 millimeter thick along joints in the fine-grained rocks of this -area. Persons who have visited Culberson County more recently report -that even minute traces of the turquoise are now difficult to find at -the old prospect pits. However, further prospecting in the area might -yield some additional localities. - -Small amounts of turquoise have been reported near El Paso, El Paso -County, and also in volcanic rocks near the Jeff Davis-Brewster County -line, north of Alpine. - -A small amount of turquoise has been mined from several localities a few -miles northwest of Sierra Blanca in the Sierra Blanca Mountains of -Hudspeth County. - - - - - GLOSSARY - - - Amorphous--without definite molecular structure; not crystalline. - Baroque stone--an irregularly shaped, polished stone; usually applied - to tumbled stones. - Baroque pearl--an irregularly shaped pearl. - Brilliancy--reflecting much light; having brightness. - Brilliant cut--a mode of arrangement of facets commonly used on round - or oval stones. The standard American brilliant cut has 57 or - 58 facets. Most diamonds of 5 or less carats are cut in this - manner. - Cabochon--a stone cut with a flat or convex upper surface; sometimes - faceted in part. Opal, star sapphire, and agate are stones - that are frequently cut in this style (fig. 2). - Cambrian--a division of geologic time, estimated to be the time from - 550 to 440 million years ago; the oldest time division of the - Paleozoic era. - Carat--a unit of weight equal to 1/5 of a gram or 0.2 gram. One ounce - avoirdupois is equal to 141.75 carats. - Cleavage--the tendency of certain minerals to split in particular - directions yielding relatively smooth plane surfaces. - Conchiolin--an organic albuminoid substance found in pearls. - Conchoidal--a type of fracture having curved concavities or the - approximate shape of one-half of a bivalve shell. Glass has - excellent conchoidal fracture. - Cretaceous--a division of geologic time, estimated to be the time from - 135 to 60 million years ago; youngest division of the Mesozoic - era. - Crown--that portion of a faceted gem above the girdle; the upper - portion of a facet-cut gem (fig. 6). - Cryptocrystalline--composed of very fine or microscopic crystals. - Crystal--the regular polyhedral form, bounded by plane surfaces, that - is assumed by a mineral under suitable conditions. Crystals - have definite external symmetry and internal molecular order. - Crystalline--possessing definite internal molecular order; not - amorphous. - Cubic--in the general shape of a cube. The isometric crystal system is - often called the cubic system. - Culet--the very bottom portion of a faceted gem; the point or line - formed by the intersection of the lowest pavilion facets (fig. - 6). - Dendritic--branching or tree-like in form. - Diaphaneity--relative transparency. The diaphaneity of a mineral is - described as transparent, translucent, opaque, etc. - Dike--a tabular rock body, usually igneous in origin, which cuts - across the surrounding rock strata. - Dispersion--a measure of the ability of gemstones to separate complex - or white light into its component colors; often illustrated - with a prism. Gemstones that are capable of separating colors - of light widely are said to have high dispersion; gemstones - not so capable of separating white light into colors are said - to have low dispersion. - Dopping--the act of cementing a gemstone, either rough or partly - finished, to a dop-stick. - Dop-stick--the wooden stick or cylindrical piece of metal to which a - gemstone is cemented to facilitate handling during cutting and - polishing. - Dop-wax--the agent or cement used to secure a gemstone to a dop-stick. - Emerald cut--a rectangular or square faceted stone with beveled - corners whose surfaces are covered with several series of - rectangular facets. - Eocene--a division of geologic time, estimated to be the time from 50 - to 40 million years ago; one of the older divisions of the - Cenozoic era. - Extrusive rock--igneous rock that has been extruded or forced out onto - the earth's surface. - Facet--a single plane polished surface on a faceted gem. - Facet head--a device used in the cutting and polishing of faceted - gems; used to control the placement of facets and their - relative angles (fig. 7). - Facet table--the equipment used in the cutting and polishing of - faceted gems and the table on which most of the equipment is - mounted (fig. 7). - Feldspar--a group of closely related silicate minerals including - orthoclase, microcline, sanidine, plagioclase, labradorite, - and others. - Fire--the reflections of variously colored light from a precious opal; - also the different colors of light reflected from a faceted - gem owing to the dispersion of the mineral. - Fracture--the texture of a freshly broken surface other than a - cleavage surface, described as conchoidal, even, splintery, - etc. - Gem--a cut and polished gemstone. - Gemology--the science dealing with the study of gemstones. - Gemstone--a mineral suitable for cutting into a gem; the term - gemstones is frequently used collectively to include both cut - and polished stones and rough stones. - Geode--a rounded or spherical rock cavity; commonly lined with - crystals. - Girdle--the portion of a faceted gem separating the crown from the - pavilion; the girdle may or may not be polished and usually - contains about 2 percent of the total depth of the gem (fig. - 6). - Gneiss--a coarse-grained metamorphic rock having segregations of - granular and platy minerals that give it a more or less banded - appearance without well-developed schistosity. - Grain (pearl grain)--a unit of weight equal to 0.05 gram or 0.25 - carat; not the same as the Troy grain. - Granite--a granular igneous rock composed mostly of quartz, feldspar, - and commonly mica and/or hornblende. - Hexagonal--having six angles and six sides; a crystal system in which - the crystal faces are referred to four intersecting axes; - three of these axes are equal, lie in the same plane, and - intersect at angles of 60 degrees; the fourth axis is - perpendicular to the other three. - Igneous rock--rock formed by solidification from a hot melt. - Index of refraction--a measure of the relative ability of a gemstone - to "bend" incident light rays; sine of the angle of incidence - of a light ray divided by the sine of the angle of refraction. - Intrusive rock--rock that has been pushed (usually in a molten state) - among pre-existing rock strata, commonly along faults or - fissures. Intrusive rocks do not reach the earth's surface but - are commonly exposed at the surface by later erosion. - Isometric--a crystal system in which the crystal faces are referred to - three equal intersecting axes at right angles to each other. - Lap--a disc-shaped piece of metal or other material which is - impregnated with diamond dust, or some other cutting or - polishing agent, that is revolved while the gemstone is worked - against it. - Lap plate--a metal plate to which a cutting or polishing lap is - attached, usually by means of a threaded bolt and wing nut. - The lap plate is attached to the shaft which is turned by the - motor under the facet table. - Lapidary--one who practices the lapidary arts; a gem cutter. - Limestone--a sedimentary rock composed mostly of calcium carbonate. - Luster--the appearance of the freshly broken or unweathered surface of - a mineral in reflected light (p. 5). - Main facet--as applied to the standard American brilliant cut, one of - the first eight facets cut on either the crown or pavilion of - a gem (fig. 6). - Matrix--the material in which a specific mineral is embedded; also the - rock to which one end of a crystal is attached. - Metamorphic rock--rock that has been changed from its original state - by heat, pressure, chemical action, or some combination of - these factors. - Millimeter--^1/_1_0 centimeter; approximately ^1/_2_5 inch. - Mineralogy--the science concerned with the study of minerals, - including their occurrence, composition, forms, properties, - and structure. - Monoclinic--a crystal system in which the crystal faces are described - in relation to three intersecting unequal axes, two of which - are at right angles and the third inclined. - Oligocene--a division of geologic time, estimated to be the time from - 40 to 28 million years ago; part of the Cenozoic era. - Opaque--does not transmit light. - Orbicular--containing orbs or spherical or eye-like markings or - structures. - Orthorhombic--a crystal system in which crystal faces are referred to - three unequal intersecting axes at right angles. - Pavilion--the portion of a faceted gem below the girdle (fig. 6). - Pegmatite--a body of coarse-grained intrusive igneous rock, commonly - lens or dike shaped. - Perthitic--a plaid-patterned structure resulting from intermixture of - soda- and potash-rich feldspars. - Phantom crystal--a crystal outline seen within another crystal, mostly - due to entrapping of inclusions during the crystal's growth. - Pleochroism--the property of transmitting different colors of light in - different crystallographic directions. - Point--a unit of weight equal to ^1/_1_0_0 (0.01) carat. - Porous--containing pores or void spaces. - Precambrian--a division of geologic time, estimated to be all of - geologic time prior to 550 million years ago; the time before - the Paleozoic era. - Preform--a gemstone that has been ground to a rough outline of the - finished shape of a gem. - Rhyolite--a fine-grained extrusive or shallow intrusive igneous rock - of approximately the same composition as granite. - Rough--uncut, not worked by a lapidary, not cut and polished. - Schist--a metamorphic rock that contains an abundance of oriented - platy minerals that enable the rock to be split with relative - ease parallel to the flat surfaces of the platy minerals. - Silicified--replaced by or containing a large amount of quartz or - silica. - Skill facet--a term often used for the pavilion girdle facets of the - standard American brilliant cut (fig. 6). - Specific gravity--the weight in air divided by the loss of weight in - water at a given temperature, or the weight of an object in - air divided by the weight of an equal volume of water; also - called relative density; the most commonly used standard - temperature for this measurement is 4° C. or 39.2° F. - Star facet--one of the eight facets surrounding the table facet of a - standard American brilliant cut (fig. 6). - Step cut--a mode of faceting in which the surface of the gem is - covered by a series of square or rectangular facets; stones - thusly cut are usually square, rectangular, or irregular with - straight sides in outline. - Streak--the color of a mineral when finely powdered; usually - determined by rubbing the mineral against a piece of unglazed - porcelain. - Symmetry--the number, location, and balanced arrangement of crystal - faces in reference to the crystallographic axes or other - crystallographic planes or directions. - Synthetic gem--a gemstone manufactured by man that has approximately - the same chemical composition and properties as a natural - gemstone. - Table facet--the large horizontal facet found on the crown of many - gems, often called simply the table (fig. 6). - Tenacity--the resistance of minerals to breakage, described by such - terms as malleable, ductile, sectile, and brittle (p. 6). - Termination--the end of a crystal that is completely enclosed by - crystal faces, the crystal end that is not attached to the - matrix. - Tertiary--a division of geologic time, estimated to be the time from - 60 to 1 million years ago; the Tertiary includes the - Paleocene, Eocene, Oligocene, Miocene, and Pliocene epochs - (from oldest to youngest). - Tetragonal--having four angles; a crystal system in which the crystal - faces are referred to three axes at right angles to each - other, two of which are equal and the third longer or shorter. - Translucent--allowing the passage of light but diffusing it - sufficiently so that objects on the other side cannot be - clearly distinguished. - Transparent--clear, allowing free passage of light so that objects on - the other side can be readily distinguished; opposite of - opaque. - Triclinic--a crystal system in which the crystal faces are referred to - three unequal axes, none of which are at right angles. - Tumbling--a process of polishing irregularly shaped gemstones (p. 17). - Vein--a tabular, irregular, or twisting mineral deposit that is thin - in relation to its length and breadth, usually the result of - solution or hydrothermal activity. - Vitreous--having luster, general appearance, or physical properties - similar to glass. - Vug--an unfilled rock cavity, commonly lined with crystals; may later - become filled by minerals owing to solution or hydrothermal - activity. - - - - - SELECTED REFERENCES - - -Anderson, B. W. (1948) Gem testing: Emerson, New York. - -Baker, C. L. (1935) Metallic and non-metallic minerals and ores -(precious stones), _in_ The geology of Texas, Vol. II, Structural and -economic geology: Univ. Texas Bull. 3401, Jan. 1, 1934, pp. 568-569. - -Barnes, V. E. (1940) North American tektites: Univ. Texas Pub. 3945, -Dec. 1, 1939, pp. 477-582. - -Dake, H. C., Fleener, F. L., and Wilson, B. H. (1938) Quartz family -minerals: Whittlesey House, McGraw-Hill Book Company, Inc., New York. - -Ford, W. E. (1932) A textbook of mineralogy (4th ed.): John Wiley and -Sons, Inc., New York. - -Kraus, E. H., and Slawson, C. B. (1947) Gems and gem materials (5th -ed.): McGraw-Hill Book Company, Inc., New York. - -Kunz, G. F. (1892) Gems and precious stones of North America (2d ed.): -Scientific Publishing Company, New York. - -Pough, F. H. (1953) A field guide to rocks and minerals: Houghton -Mifflin Company, Boston. - -Simpson, B. W. (1958) Gem trails of Texas: Granbury, Texas. - -Sinkankas, John (1955) Gem cutting: D. Van Nostrand Company, Inc., -Princeton, New Jersey. - ----- (1959) Gemstones of North America: D. Van Nostrand Company, Inc., -Princeton, New Jersey. - -Smith, G. F. H. (1958) Gemstones (13th ed.), revised by F. C. Phillips: -Methuen and Company, Ltd., London. - -Sperisen, F. J. (1950) The art of the lapidary: The Bruce Publishing -Company, Milwaukee, Wisconsin. - -Sterrett, D. B. (1913) Gems and precious stones, _in_ Mineral resources -of the United States, Calendar Year 1912, Part II, Non-metals: U. S. -Geol. Survey, pp. 1023-1060. - - - - - Plate I - - - [Illustration: A -Gem-quality celestite crystals from Travis County, Texas. Twice natural - size. Lower portion of the crystals is colorless; the tips are dark - blue.] - - [Illustration: B - Opalized wood from the Texas Gulf Coastal Plain. Specimen at left is -rich brown and tan; specimen at right is fossil palm wood and is black, - reddish brown, and white. One-third natural size.] - - - - - Plate II - - - [Illustration: A - Gem-quality garnet crystals and faceted gem from Gillespie County, - Texas. Natural size.] - - [Illustration: B - Labradorite from Brewster County, Texas. Both stones are pale yellow. - One and a half times natural size.] - - - - - Plate III - - - [Illustration: A - Pink microcline crystal from Burnet County, Texas.] - - [Illustration: B -Smoky quartz from Burnet County, Texas. Natural size. Colorless crystal - at center back is included for color comparison.] - - - - - Plate IV - - - [Illustration: Polished agate from gravels of the Rio Grande near -Zapata, Zapata County, Texas. Bands are blue and gray; other inclusions - are brown, yellow, and reddish. One and a half times natural size.] - - - - - Plate V - - - [Illustration: A -Texas tektites (bediasites) showing variety of surface features. Natural - size.] - - [Illustration: B -Topaz crystal from a pegmatite dike near Streeter, Mason County, Texas. - Natural size. Measurements: 1½ by 1-5/8 by 3 inches; weight: 194 grams - (970 carats); pale blue; mostly gem quality.] - - - - - Plate VI - - - [Illustration: A - Topaz from stream gravels near Streeter, Mason County, Texas. Natural -size. Left to right: colorless worn pebble; emerald-cut pale-blue topaz, - weight 10 carats; pale-blue worn pebble, weight 205 carats; step out - sky-blue topaz, weight 13 carats; pale-blue worn pebble.] - - [Illustration: B - Tourmaline crystals in schist from Llano County, Texas.] - - - - - Index - - - A - actinolite: 26 - agate: 20, 28, 38 - agatized wood: 27 - allanite: 21 - almandite: 22 - amazonite: 23 - amazon stone: 23 - amber: 18 - amethyst: 25 - Amethyst Hill: 25 - amorphous gemstones: 9 - andalusite: 30 - Arkansas: 19 - Armstrong County: 21 - augite: 18, 28 - - - B - Baringer Hill, Llano County: 21, 26 - baroque pearls and/or stones: 17, 25 - bediasite (tektite): 28-29, 39 - beryl: 18 - Big Bend National Park: 27 - biotite: 23 - Blanco County: 18, 22 - Brazos County: 29 - Brazos River: 25 - Brewster County: 18, 23, 24, 25, 26, 27, 28, 31, 36 - brilliancy: 5 - brilliant cut, standard American: 13, 15, 16 - Brown County: 19 - Burleson County: 29 - Burnet County: 20, 22, 23, 25, 26, 30, 37 - - - C - cabochon gems: 10-12 - Caddo Lake: 25 - carbuncle: 22 - carnelian: 27 - cassiterite: 23, 29 - celestite: 19, 35 - chalcedony: 27 - geodes: 26 - chuck: 15, 17 - citrine: 25-26 - cleavage: 6, 13 - coal: 22 - Coke County: 19 - color: 5 - Colorado River: 25 - Concho River: 25 - crown girdle facets: 16, 17 - crown of gemstone: 15, 16 - crystals: 7-9 - crystal systems: 7 - crytolite: 21 - Culberson County: 22, 23, 25, 26, 31 - culet: 13 - cutting and polishing: 10-17 - cutting lap: 13 - - - D - DeWitt County: 29 - diamond: 19 - saw: 10, 11 - diaphaneity: 5 - dispersion: 6 - dopping: 12, 13 - dop-stick: 12, 15, 17 - dop-wax: 12, 15, 17 - dravite: 30 - durability: 6 - Duval County: 21, 24 - - - E - El Paso County: 22, 30, 31 - emerald cut: 15 - epidote: 19-20 - - - F - facet, kinds of: 13 - main: 16 - skill: 16 - table: 13, 14 - faceted gems and/or stones: 10, 13-17 - Fayette County: 20, 29 - fergusonite: 21 - fire: 5 - Fisher County: 19 - fluorite: 20, 21 - Foard County: 19 - fossil wood: 20-21, 22 - fracture: 6 - Franklin Mountains: 18 - - - G - gadolinite: 21-22 - garnet: 20, 22, 36 - gemstones, by kinds: 18-31 - geodes, celestite: 19 - Georgia: 29 - Gillespie County: 18, 22, 23, 25, 26, 30, 36 - girdle facets: 16 - gneiss: 22 - Gonzales County: 20, 29 - grain: 25 - gram: 7 - graphite: 30 - Grimes County: 29 - grinding: 12 - Guadalupe River: 25 - Gulf Coast: 25 - Gulf Coastal Plain: 18, 20, 22, 35 - - - H - hardness: 6 - Hudspeth County: 18, 20, 22, 24, 25, 26, 27, 28, 31 - - - I - index of refraction: 5 - - - J - jasper: 27-28 - Jeff Davis County: 26, 27, 28, 31 - jet: 22 - - - K - Kinney County: 28 - - - L - labradorite: 23, 36 - Lake Buchanan: 21 - Lampasas County: 19 - lap plate: 13 - Lavaca County: 29 - Lee County: 20, 29 - lignite: 22 - Live Oak County: 21 - Llano County: 18, 19, 20, 21, 22, 23, 25, 26, 30, 31, 40 - Llano River: 25 - luster: 5 - - - M - Madeira topaz: 29 - Mason County: 20, 22, 23, 26, 29, 30, 39, 40 - Massachusetts: 29 - Maverick County: 18 - microcline: 20, 21, 23-24, 29, 37 - Mohs scale of hardness: 6 - moonstone: 28 - Mount Bonnell: 19 - muscovite: 23 - - - N - natural glass: 18, 24, 28 - Needle Peak, Presidio County: 27 - nivenite: 21 - Nolan County: 19 - Nueces River: 25 - - - O - obsidian: 24, 29 - Oklahoma: 29 - opal: 20, 24 - opalized wood: 35 - orbicular jasper: 28 - ounce: 7 - - - P - Packsaddle Mountain: 23 - Packsaddle schist: 30 - palm wood: 21, 35 - Palo Duro Canyon: 21 - pavilion: 13, 16 - facets: 16 - girdle facets: 16, 17 - pearl: 24-25 - pegmatites and/or pegmatite dikes: 18, 20, 21, 22, 23, 26, 29, 39 - petrified wood: 26 - phantom crystals: 26 - pistacite: 20 - pleochroism: 5 - point: 7 - polishing: 17 - lap: 13, 16 - preformed stone: 16 - preforming: 15 - Presidio County: 20, 22, 24, 25, 26, 27, 28 - properties of gemstones: 5-7 - - - Q - quartz: 20, 21, 23, 25-28, 29, 30 - smoky: 38 - - - R - radioactive elements: 22 - radioactivity of gadolinite: 21 - rarity: 6 - Reeves County: 26, 27 - Rio Grande: 25 - gravels of: 21, 27, 38 - Valley: 27 - rock crystal: 26 - rose quartz: 26 - - - S - Sabine River: 25 - sanding: 12 - sanidine: 28 - sawing: 10 - scheelite: 20 - schorl: 30 - size: 7 - "skill" facets: 16 - "slab" of gem materials: 11 - Smithsonian Institution: 21 - smoky quartz: 23, 26, 37 - smoky topaz: 29 - Spanish topaz: 29 - specific gravity: 7 - spinel: 18, 28 - star facets: 17 - step cut: 15 - streak: 6 - synthetic gems: 7 - - - T - table facet: 13, 15 - tektite (bediasite): 28-29, 39 - tenacity: 6 - thorogummite: 21 - topaz: 23, 26, 29-30, 39, 40 - quartz: 29 - tourmaline: 26, 29, 30-31, 40 - Town Mountain, Llano County: 26, 30 - transparency: 6 - Travis County: 19, 35 - Trinity River: 25 - tumbled gems: 17 - turquoise: 31 - - - U - U. S. National Museum: 30 - - - V - value of gemstones: 6, 7 - Val Verde County: 24 - valverdites: 24 - Van Horn, Hudspeth County: 27 - - - W - Walker County: 29 - Washington County: 20 - Webb County: 21 - weight, units of: 7, 25 - - - Z - Zapata County: 38 - - - - - Transcriber's Notes - - ---Silently corrected a few typos. - ---Renumbered figures 6 and 7 (and references to them) to correspond to - their order in the printed book. - ---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_. - - - - - - - -End of the Project Gutenberg EBook of Texas Gemstones, by Elbert A. 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