,,bureau ,,of ,,economic ,,geology ,the ,university of ,texas at ,austin ,austin1 ,texas #ghgab ,,john ,t4 ,,lonsdale1 ,director ,report of ,investigations--,no4 #db ,texas ,gemstones ,by ,elbert ,a4 ,king1 ,jr4 ,february #aifa ,second ,printing--,february #aifc ,third ,printing--,september #aigb ,fourth ,printing--,march #aihc ,fifth ,printing--,august #aiia ,contents ,page ,introduction #e ,properties of gemstones #e ,crystals #g ,cutting and polishing of gemstones #aj ,cabochon gems #aj ,faceted gems #ac ,tumbled gems #ag ,texas gemstones #ah ,amber #ah ,augite #ah ,beryl #ah ,celestite #ai ,diamond #ai ,epidote #ai ,fluorite #bj ,fossil wood #bj ,gadolinite #ba ,garnet #bb ,jet #bb ,labradorite #bc ,microcline #bc ,obsidian #bd ,opal #bd ,pearl #bd ,quartz #be ,crystalline varieties #be ,amethyst #be ,citrine #be ,rock crystal #bf ,rose quartz #bf ,smoky quartz #bf ,cryptocrystalline varieties #bg ,chalcedony #bg ,agate #bg ,agatized wood #bg ,carnelian #bg ,jasper #bg ,sanidine #bh ,spinel #bh ,tektite 7bediasite7 #bh ,topaz #bi ,tourmaline #cj ,turquoise #ca ,glossary #cb ,selected references #cd ,index #da ,illustrations ,figures-- ,page #a4 ,typical crystal form of three common ,texas gemstones #i #b4 ,variations of the cabochon cut #aj #c4 ,diamond saw #aa #d4 ,cabochon properly attached to dop-stick #ab #e4 ,cabochons at various stages of cutting and polishing #ab #f4 ,nomenclature of the standard ,american brilliant cut #ac #g4 ,facet table #ad #h4 ,grinding the table facet on a rough stone #ae #i4 ,stone dopped to table facet #ae #aj4 ,preformed stone dopped to table facet #af #aa4 ,proper sequence of cutting of the pavilion facets #af #ab4 ,proper placing of pavilion girdle facets #ag #ac4 ,proper sequence of cutting of crown facets #ag #ad4 ,common crystal form of ,travis ,county celestite #ai #ae4 ,common crystal form of fluorite #bj #af4 ,crystal faces on microcline specimen shown in ,plate ,,iii #bc #ag4 ,common crystal form of spinel #bh #ah4 ,crystal faces on topaz crystal shown in ,plate ,v #bi #ai4 ,cross section through irregularly colored stone #cj #bj4 ,common crystal form of ,llano ,county tourmaline #ca ,plates-- ,page ,i4 ,a1 ,gem-quality celestite crystals from ,travis ,county4 ,b1 ,opalized wood from the ,texas ,gulf ,coastal ,plain #ce ,,ii4 ,a1 ,gem-quality garnet crystals and faceted gem from ,gillespie ,county4 ,b1 ,labradorite from ,brewster ,county #cf ,,iii4 ,a1 ,pink microcline crystal4 ,b1 ,smoky quartz4 ,both from ,burnet ,county #cg ,,iv4 ,polished agate from gravels of the ,rio ,grande near ,zapata1 ,zapata ,county #ch ,v4 ,a1 ,texas tektites 7bediasites74 ,b1 ,topaz crystal from a pegmatite dike near ,streeter1 ,mason ,county #ci ,,vi4 ,a1 ,topaz from stream gravels near ,streeter1 ,mason ,county4 ,b1 ,tourmaline crystals in schist from ,llano ,county #dj ,table #a4 ,properties of some common ,texas gem minerals #h ,texas ,gemstones ,,elbert ,a4 ,,king1 ,,jr4 ,,introduction ,throughout history man has sought stones and minerals for personal adornment and ornamentation4 ,stones and minerals that are sufficiently beautiful1 durable1 and rare are known as gemstones4 ,a gemstone with only one of these qualities is less desirable than one with all three4 ,for example1 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 abrasion4 ,likewise1 a stone that is beautiful and durable may be of little interest as a gemstone because it is commonly found in great quantities4 ,to be valued highly1 gemstones must be beautiful to the eye1 durable enough to withstand wear1 and rare enough so that they are not easily obtained4 ,properties of ,gemstones ,the beauty of gemstones is mostly dependent on their color1 diaphaneity1 brilliancy1 luster1 and fire4 ,any one or a combination of these properties render stones desirable as gems4 ,color is very important in many gemstones4 ,the color of transparent varieties should be distinct enough to be pleasing to the eye1 yet not so dark as to appear black or opaque4 ,it is generally more desirable that the gemstone be of even color and not appear 8patchy0 or 8streaked40 ,however1 some opaque or translucent stones such as agate owe their popularity chiefly to the variety of colors and designs within a single piece4 ,some transparent gemstones exhibit different colors when viewed in different directions4 ,for example1 some fine blood-red rubies appear brownish when viewed in a particular direction4 ,the gemstone should be cut so that its finest color is most prominently displayed4 ,this ability of some gemstones to exhibit different colors when viewed in different directions is called pleochroism4 ,diaphaneity is the relative ability of stones to transmit light4 ,diaphaneity is described by terms such as transparent1 translucent1 and opaque4 ,transparency is highly desirable in stones such as diamond that are commonly facet-cut to reflect light4 ,the gemstone should be water clear and free from inclusions and cracks so that it transmits light freely1 but there are stones that do not exhibit this property that are prized as gemstones4 ,for example1 turquoise may appear to be completely opaque and not transmit any light1 but it is sought for its fine blue color4 ,the brilliancy of gemstones is largely dependent on their index of refraction4 ,the index of refraction is a measure of the ability of a cut gemstone to 8bend0 light rays and reflect them from the bottom facets back through the top of the stone4 ,of course1 brilliancy is not noted in opaque or faintly translucent stones4 ,the index of refraction of gemstones is expressed numerically4 ,air is the reference medium and is assigned an index of refraction of #a4jj4 ,other substances are assigned values relative to that of air1 for example1 water1 #a4cc2 topaz1 #a4fb2 diamond1 #b4db4 ,the higher the index of refraction1 the more brilliant will be the gemstone if it is properly cut and polished4 ,luster is the appearance of the mineral on a fresh surface in reflected light2 it is divided into two major categories1 metallic and non-metallic4 ,most gemstones have non-metallic luster and are described by terms such as vitreous or glassy1 resinous1 waxy1 greasy1 and pearly4 ,the fire1 or ability of gemstones to show flashes of different colors of light1 is dependent upon a property called dispersion4 ,the amount of dispersion is the extent to which the gemstone is able to separate ordinary white light into its component colors4 ,the dispersion of gemstones can also be expressed numerically but for purposes of this publication will be referred to as low1 moderate1 or high4 ,diamond is a common gemstone that has high dispersion4 ,a gemstone's durability is primarily dependent upon its hardness4 ,the ,mohs scale of hardness1 given below1 is most commonly used for gemstones and other minerals4 ,mohs ,scale of ,hardness #a4 ,talc #b4 ,gypsum #c4 ,calcite #d4 ,fluorite #e4 ,apatite #f4 ,orthoclase feldspar #g4 ,quartz #h4 ,topaz #i4 ,corundum #aj4 ,diamond ,on this scale1 the higher numbers are the harder minerals4 ,mohs is a relative1 not an absolute scale4 ,therefore1 it should not be assumed that diamond is ten times harder than talc because actually diamond is very many tens of times harder than talc4 ,however1 a particular mineral is harder than any other mineral with a lesser number1 and the scale is very convenient to use4 ,gemstones mounted in rings should have a hardness of at least seven on the ,mohs scale1 or the stones may become scuffed and scratched after a relatively short period of wear4 ,gemstones mounted in pins and brooches can be of softer material as they are not usually subjected to abrasion and rough treatment4 ,the tendency of some minerals to split with relative ease in particular directions along planes is called cleavage4 ,cleavage is also a factor determining the durability of gemstones4 ,some gemstones do not exhibit this tendency at all1 whereas others cleave in several directions4 ,the number of cleavages is always the same in any one mineral1 and the direction of cleavages is constant in relation to the crystal structure of any one mineral or gemstone4 ,it is apparent that of stones having the same hardness1 the ones lacking cleavage or having the lesser number of good cleavage directions are the most durable4 ,some stones1 such as jade and agate1 owe their durability to their compact fibrous structure1 which makes them very tough and durable even though they are not especially hard4 ,several other properties of gemstones1 although not always contributing to the beauty or desirability of gemstones1 are useful in identifying uncut specimens4 ,streak is the color of the mineral when finely powdered or1 for softer minerals1 the color obtained by rubbing the mineral against a piece of unglazed porcelain or tile4 ,the color of a mineral's streak is commonly different from the unpowdered specimen4 ,fracture is the kind of surface obtained when the mineral is broken in a direction that is not a cleavage direction4 ,fracture surfaces are described by such terms as conchoidal 7like the fracture of glass71 subconchoidal1 splintery1 even1 and uneven4 ,tenacity is the resistance of a mineral to breakage4 ,brittle minerals break relatively easily on impact4 ,malleable minerals1 such as gold1 may be flattened under a hammer into very thin sheets without breaking4 ,sectile minerals may be cut with a knife without powdering4 ,most gemstones1 even diamond1 are brittle4 ,it is only natural to value most those gemstones that are not common or easy to obtain4 ,emerald owes its longstanding popularity to its fine green color1 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 common4 ,rarity is not the only factor affecting the value of gemstones4 ,freedom from internal imperfections1 quality of cutting1 color1 and size must also be considered in cut and polished gemstones4 ,internal imperfections1 such as inclusions and cracks1 detract from the appearance of gemstones and interfere with the passage of light between the facets2 consequently1 gemstones containing these imperfections are not valued as highly as those without them4 ,poor cutting or polishing detract from the beauty and thus from the value of gemstones4 ,unpopular or poor color commonly causes gemstones to be less valuable4 ,rich green emeralds are exceedingly prized1 whereas very pale green emeralds are relatively inexpensive4 ,diamonds that have the least hint of yellow are never valued as highly as pure colorless1 pink1 or blue stones4 ,few persons find the yellowish color attractive1 unless it is a vivid canary yellow4 ,size is important in determining the value of gemstones but not as important as perfection4 ,a badly flawed gemstone of large size may be worth only a slight fraction of the value of a smaller perfect one4 ,gemstone size is usually measured in carats1 a unit of weight1 although millimeter size is sometimes used4 ,five carats is equal to #a gram and approximately #bh grams is equal to #a ounce avoirdupois4 ,one one-hundredth 7#j4ja7 of a carat is called a point1 and this term is often used1 especially pertaining to very small gemstones4 ,the term used to compare the relative weights of minerals and gemstones is specific gravity1 which is expressed numerically in relation to water4 ,water is assigned the value of #a4jj4 ,therefore1 at a given temperature a gemstone having a specific gravity of #b4jj is twice as heavy as an equal volume of water4 ,a #a-;carat sapphire 7specific gravity about #d4jj7 will be smaller than a #a-;carat amethyst 7specific gravity about #b4fe7 because the heavier material will occupy less volume to have the same weight4 ,a summary of properties helpful in identification of common ,texas gem minerals is given in ,table #a4 ,comparatively recently in the history of gemstones1 man has succeeded in the production of synthetic gems that have properties closely approaching those of many natural gemstones4 ,to the untrained eye some synthetic gems may appear identical to natural stones1 but synthetic gems can be detected with little difficulty by a properly equipped expert4 ,although most synthetic gems are inexpensive1 their manufacture has not adversely affected the value of natural gemstones but instead has increased the demand for fine natural gems4 ,crystals ,gemstones that have an orderly internal molecular arrangement are referred to as crystalline4 ,this internal order is commonly reflected in the external shape of 8rough0 or uncut gemstones4 ,the resultant shape is a polyhedral solid bounded by planes and called a crystal4 ,well-formed crystals are formed in nature only under relatively ideal conditions of temperature1 pressure1 and space4 ,the specific temperatures and pressures involved vary with different minerals1 but most crystals need space in which to form so that their 8growth0 is not impaired by surrounding rocks and minerals4 ,however1 some minerals1 such as garnet and tourmaline1 can grow in metamorphic rocks by recrystallization of minerals in the metamorphic rocks4 ,the size of crystals varies from microscopic to tens of feet4 ,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 7fig4 #a74 ,frequently gemstones are found as abraded stream-rolled pebbles1 fragments1 or masses that do not show crystal form4 ,crystals of the same mineral from different locations commonly show somewhat different crystal forms owing to slight differences in composition or conditions of formation4 ,mineralogists and crystallographers classify crystals by the symmetry that they exhibit4 ,the crystal systems are 7#a7 isometric or cubic1 7#b7 tetragonal1 7#c7 hexagonal1 7#d7 orthorhombic1 7#e7 monoclinic1 and 7#f7 triclinic4 ,a complete description of the classification of crystals can be found in almost any mineralogy text 7see ,selected ,references1 p4 #cd74 ,table #a4 ,properties of some common ,texas gem minerals4 ,,mineral ,,composition ,,hardness ,,specific ,,index ,,of ,,common ,,gravity ,,refraction ,,colors ,,in ,,texas ,amber fossil resin #b4j-b4e #a4je-a4aj about #a4ed brown1 yellow ,augite ,ca,mg,si,o #e4j-f4j #c4b-c4f #a4fj-a4ga greenish brown1 black ,beryl ,be,al7,si,o7 #g4e-h4j #b4fc-b4hj #a4ef-a4fj pale blue1 colorless1 greenish ,celestite ,sr,s,o #c4j-c4e #c4ie-c4ih #a4fb-a4fc colorless1 blue ,epidote ,h,ca7,al1 #f4j-g4j #c4be-c4ej #a4gb-a4gg yellowish ,fe7,si,o green1 brownish green ,fluorite ,ca,f #d4j #c4j-c4be #a4dcd colorless1 violet1 yellow1 green ,garnet ,fe,al7,si,o7 about #g4e #d4be about #a4hc red1 deep 7,almandite7 red1 brownish red ,labradorite ,na,al,si,o #ej to #f4j-f4e about #b4f about #a4ef yellowish1 #cj ,ca,al,si,o #ej grayish to #gj ,microcline ,k,al,si,o #f4j-f4e #b4ed-b4eg #a4eb-a4ec pink1 red1 bluish1 greenish1 white ,obsidian volcanic glass #e4j-e4e #b4c-b4e #a4de-a4ec dark gray1 black1 brownish ,opal ,si,on,h,o #e4e-f4e #a4i-b4c #a4dc white1 pink1 bluish1 brown1 gray ,quartz ,si,o #g4j #b4fe-b4ff #a4edd-a4eec colorless1 7,crystalline7 violet1 yellow1 brown ,tektite natural glass #e-f #b4cc-b4dd #a4dh-a4eb dark brown1 7,bediasite7 greenish brown ,topaz ,al7,f,,oh7,si,o #h4j #c4d-c4f #a4fj-a4fc colorless1 bluish1 sky blue ,tourmaline ,h,al7,b,,oh7,si,o #g4j-g4e #b4ih-c4bj #a4fb-a4fd black1 dark brown ,some gemstones1 such as opal and obsidian1 never occur as crystals owing to a lack of internal structural order4 ,such gemstones are termed amorphous1 or without form4 ,amorphous gemstones mostly occur in nature as irregular lumps or masses1 cavity fillings1 or veins4 ,illustration3 ,fig4 #a4 ,typical crystal form of three common ,texas gemstones4 ,,garnet ,,tourmaline ,,quartz ,,cutting ,,and ,,polishing ,,of ,,gemstones ,there are two types of widely used gemstone cuts4 ,opaque or figured gemstones are usually cut with a rounded upper surface and a flat or rounded back4 ,a stone cut in this fashion is termed a cabochon or is said to be cabochon cut4 ,there are several variations of this mode of cutting 7fig4 #b74 ,precious opal1 agate1 jade1 star sapphire1 and fossil wood are some of the stones that are cut mostly as cabochons4 ,transparent gemstones are usually cut with many plane polished surfaces4 ,such stones are called faceted1 and the process of cutting and polishing these stones is called faceting4 ,emerald1 diamond1 topaz1 and garnet are examples of gemstones that are commonly seen as faceted stones4 ,illustration3 ,fig4 #b4 ,variations of the cabochon cut4 ,left to right3 double cabochon2 flat cabochon2 simple cabochon2 hollow cabochon4 ,the cutting of gemstones1 although sometimes tedious and time consuming1 is not especially difficult or complex4 ,however1 like most arts and crafts1 technique and ability should improve with practice and experience4 ,there are currently many amateur gem cutters in ,texas4 ,a complete set of equipment necessary to cut cabochon stones may be purchased for as little as #ej4jj or #fj4jj4 ,most amateur cabochon cutters have equipment that cost less than #ajj4jj which enables them to do very fine work on many gem materials4 ,facet cutting requires more precise equipment1 and a complete array of such usually costs more than #ajj4jj1 although less expensive equipment can be obtained4 ,the beginning gem cutter or lapidary who is willing to assemble and make some of his own equipment can reduce his initial expenses considerably4 ,cabochon ,gems ,the procedures listed herein for gem cutting do not apply to all gemstones4 ,stones that are especially brittle1 soft1 or difficult to polish require additional procedures or special techniques4 ,many lapidaries may deviate from these procedures4 ,some of the steps of cutting and polishing are merely matters of personal opinion and vary somewhat from cutter to cutter4 ,there are several detailed texts on the art of gem cutting2 the descriptions herein are designed to give the reader only a general idea of the procedures and techniques involved4 ,the cutting and polishing of cabochons require several steps4 ,the initial step is sawing4 ,assuming that the rough gem material is large enough to be sawed 7larger than about half an inch in diameter71 it is clamped into the carriage of a diamond saw 7fig4 #c7 and cut into slices about -inch thick4 ,the blade of the saw is mild steel that has been impregnated with diamond dust around the edge1 hence the name diamond saw4 ,the blade is rotated rapidly1 and the material to be cut is 8fed0 to the blade by a sliding carriage on which the gem material is clamped4 ,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 minutes4 ,the lower portion of the saw blade is immersed in a mixture of kerosene and oil1 and the rotating saw blade carries with it some of the kerosene-oil mixture2 this acts as a coolant and lubricant for both the saw blade and the material being cut4 ,without this lubricant1 the heat generated by sawing would shatter most gem materials and also damage the saw blade4 ,as this 8slicing0 or sawing of the material usually takes several minutes1 a weight and pulley are generally used to give the gem material the necessary pressure against the saw blade4 ,when cut through1 the 8slab0 of gem material falls into the kerosene-oil mixture at the bottom of the saw or onto a special platform that cushions its fall4 ,illustration3 ,fig4 #c4 ,diamond saw4 ,motor ,clamp ,diamond-charged blade ,carriage ,stone ,weight ,after being sawed1 the slab of gem material is examined1 and the location and size of the stones to be cut from the slab are determined4 ,the desired outline of the shape of the gem to be cut is marked on the slab with a pointed piece of aluminum rod2 ordinary pencil marks are not used because they wear away too quickly in the cutting process4 ,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 slab1 the excess material is trimmed away by a smaller diamond saw known as a trim-saw4 ,in some slabs the excess material can be broken and 8nibbled0 away with a strong pair of pliers4 ,the remaining portion of the stone is usually held by hand and ground to the desired shape using the previously scribed mark as a guide4 ,this is done using a relatively coarse-grained 7about #aej grit7 specially made carborundum grinding wheel4 ,now that the desired outline has been obtained1 the stone is firmly affixed to a slender wooden or hollow aluminum dop-stick 7fig4 #d74 ,the process whereby the stone is attached to the dop-stick with a specially compounded jeweler's wax is called dopping4 ,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 gemstone4 ,the stone is likewise heated1 and the wax is applied to the back of the stone while both wax and stone are hot4 ,upon cooling1 the wax firmly fixes the stone to the dop-stick4 ,the dop-stick allows the lapidary to have firm control of the stone during all later stages of cutting and polishing4 ,illustration3 ,fig4 #d4 ,cabochon properly attached to dop-stick4 ,,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 shape4 ,the stone is then worked against a much finer-grained 7about #bbj grit7 grinding wheel to remove the irregularities left by the coarse grinding and to further smooth and shape the surface of the gemstone4 ,at all times while grinding1 a small flow of water should be directed on the grinding wheel to keep the stone cool4 ,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 wheel4 ,if the lapidary keeps the surface of the grinding wheel wet1 there is little chance of damaging most gem materials4 ,the next phase of cabochon cutting and polishing is sanding4 ,the gemstone is worked against two sanding drums of different grit size4 ,this sanding can be done with the sandpaper surface either wet or dry1 as needed or as preferred by the lapidary4 ,however1 great care should be exercised during sanding so that the stone is not overheated4 ,overheating can easily occur whether the sandpaper is used wet or dry4 ,as in grinding1 sanding is first done on coarser grit paper 7about #cjj grit7 and last on finer paper 7about #fjj grit74 ,it is in the sanding process that the first hint of polish is noted on the surface of the stone4 ,after sanding1 the gemstone should have perfect form with no surface irregularities1 a very finely textured surface1 and only very minor scratches left from sanding4 ,the gemstone is now ready to be polished4 ,illustration3 ,fig4 #e4 ,cabochons at various stages of cutting and polishing4 ,left to right3 trimmed from slab3 ground to outline2 after rough grinding2 after sanding2 polished4 ,at this point the procedure depends on the nature of the gemstone being polished4 ,most gem materials are worked against a buffing wheel that is impregnated or saturated with a mixture of some polishing compound and water4 ,a soft felt buffing wheel with cerium oxide as the polishing agent is used for many materials4 ,the mixture of cerium oxide and water is usually applied to the buffing wheel with a small brush4 ,the lapidary should once more be careful not to overheat the stone4 ,if the stone becomes too hot to hold to the underside of the cutter's wrist1 it should be permitted to cool for a few seconds before continuing4 ,after polishing on the buffing wheel1 the gemstone should have a fine1 high polish and be free of any scratches or surface irregularities4 ,the finished gemstone is removed from the dop-stick by heating the dop-wax and pulling the stone loose4 ,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 cloth4 ,figure #e illustrates the desired appearance of the gemstone at the end of each of the steps of cutting and polishing4 ,faceted ,gems ,the principles involved in faceting are about the same as those in the cutting of cabochons1 but the equipment and technique are considerably different4 ,the equipment required for the facet cutting of gemstones is built into or attached to a small specially constructed table 7fig4 #g71 and the unit is commonly called a facet table4 ,most faceted gemstones are cut to obtain the largest flawless stone possible from the rough material4 ,therefore1 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 pebble4 ,the colors that can be obtained from the gemstone must also be considered1 and the cutting of the stone oriented so that its best color is displayed4 ,the lapidary also selects the orientation of the stone in relation to the cleavage or cleavages4 ,it is difficult or impossible to polish facets of gemstones that are cut parallel to a good cleavage direction4 ,illustration3 ,fig4 #f4 ,nomenclature of the standard ,american brilliant cut4 ,,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 determined1 the stone is dopped onto a special metal dop-stick that fits into the chuck of the facet head4 ,the chuck is tightened so that the position of the stone on the end of the arm of the facet head is firmly fixed1 and the facet head is adjusted so that the first facet that is cut is the horizontal1 top facet of the stone or table facet 7fig4 #f74 ,the table facet is cut by grinding the gemstone on a flat cutting lap that is diamond impregnated 7fig4 #h74 ,by minor adjustments of the facet head1 the lapidary can precisely control the location of the table facet4 ,as soon as the table facet has been ground to the proper size1 the cutting lap is removed from the lap plate1 and the polishing lap is secured in place4 ,many different kinds of polishing laps and polishing compounds may be used depending on the properties of the material being polished4 ,however1 one lap and one polishing compound are usually sufficient for each gem variety4 ,after the polishing lap is secured to the lap plate1 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 facet4 ,the polishing lap is run wet or damp with water1 as is the cutting lap1 and small amounts of the polishing compound are applied to the surface of the lap while the facet is being polished4 ,the minor scratches left by the cutting process are gradually removed1 and a fine lustrous polish develops on the facet4 ,it is especially important to take care in achieving a perfect polish on the table facet1 as this facet occupies a large area of the crown of the gemstone4 ,when the cutting and polishing of the table facet are completed1 the gemstone is still rough or uncut in all portions except for this single1 large1 polished surface4 ,illustration3 ,fig4 #g4 ,facet table4 ,water ,light ,adjusting ring ,post ,arm ,chuck ,stone ,abrasives ,,diamond ,,dust ,,calcium ,,oxide ,,lande-,a ,illustration3 ,fig4 #h4 ,grinding the table facet on a rough stone4 ,,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 7fig4 #i74 ,great care should be taken by the lapidary to insure that the table of the stone is exactly perpendicular to this axis1 or the proper placing of the later facets on the stone may become very difficult4 ,illustration3 ,fig4 #i4 ,stone dopped to table facet4 ,,table ,,facet ,,dop-,,wax ,,stone ,,dop-,,stick ,once the stone has been properly dopped to the table facet1 the lapidary is ready to proceed with the cutting of the outline of the stone4 ,if it is to be a brilliant cut1 the stone is ground perfectly round in outline2 if it is to be an emerald or step cut1 it is shaped so that it is square or rectangular in outline4 ,this process is called preforming4 ,the arm of the facet head is lowered on the post until it is horizontal1 and the stone is worked against the cutting lap until the desired shape is obtained4 ,when the preforming process is completed1 the stone should have the desired outline of the finished gem 7fig4 #aj74 ,illustration3 ,fig4 #aj4 ,preformed stone dopped to table facet4 ,,dop-,,wax ,,stone ,,dop-,,stick ,the lapidary is now ready to proceed with the cutting of the pavilion of the stone4 ,the arm of the facet head is raised to the proper angle for cutting the main pavilion facets4 ,the angle at which the main facets are cut is very critical in determining the beauty of the finished stone4 ,the required angle at which these facets must be cut varies with the refractive indices of the different varieties of gem minerals4 ,if the facets are not cut at exactly the proper angle1 light entering the top or crown of the gemstone can pass completely through the stone1 instead of being reflected back out of the crown facets4 ,the result is a dull1 lifeless stone that appears to have a 8hole0 or 8fish-eye0 in the center4 ,stones that are cut in this manner are greatly reduced in value4 ,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 post4 ,the lapidary will continually adjust this height1 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 size4 ,illustration3 ,fig4 #aa4 ,proper sequence of cutting of the pavilion facets4 ,left to right3 four main facets2 all eight main facets2 half of the pavilion girdle facets2 completed pavilion4 ,the standard ,american brilliant cut will be used as an example of facet cutting4 ,procedure for all other cuts is essentially the same to this point4 ,after the eight main pavilion facets have been cut1 the cutting angle is changed a few degrees1 the arm of the facet head rotated slightly1 and the sixteen pavilion girdle facets or 8skill0 facets1 as they are often called1 are cut 7fig4 #aa74 ,the pavilion girdle facets should meet exactly in the center of the main facets at the girdle of the stone4 ,the pavilion girdle facets should neither overlap1 nor should there be any space between them 7fig4 #ab74 ,after the pavilion girdle facets are cut1 the cutting of the pavilion of the gemstone is completed4 ,the facets are then polished on the polishing lap at the same angles and in the same order as they were cut1 and the pavilion of the gem is completely finished4 ,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 cutting4 ,before the lapidary proceeds with the cutting of the crown1 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 head4 ,the eight main facets are cut first1 with numerous adjustments being made by the lapidary to insure that the proper angle is maintained 7fig4 #ac74 ,then the cutting angle is changed a few degrees1 the arm of the facet head rotated slightly1 and the crown girdle facets are cut4 ,the crown girdle facets are placed very similarly to the pavilion girdle facets except that they are shorter4 ,the crown girdle facets should be joined in exactly the same way as the pavilion girdle facets4 ,when these facets are properly cut1 the cutting angle is again changed1 the arm rotated1 and the eight star facets are cut4 ,this completes the cutting of the crown of the stone4 ,the cutting lap is removed from the lap plate1 and the polishing lap is secured into place4 ,the facets are carefully polished in the same order that they were cut4 ,after the last star facet has been polished1 the stone is removed from the dop-stick4 ,any excess dop-wax is removed from the stone by means of a solvent1 and the full beauty of the finished gem is revealed4 ,tumbled ,gems ,one other method of finishing gemstones that deserves mention is tumbling4 8,baroque0 or 8free-form0 stones are produced in this manner4 ,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 grit4 ,the barrel is turned by means of a small motor1 and the abrasion of the pebbles and grit against each other tends to round the pebbles and give them a finely pitted surface4 ,progressively finer and finer carborundum grit is used1 and eventually a polishing compound4 ,the result is several pounds of well-polished gem pebbles of various shapes and sizes4 ,these baroque stones have found recent favor in costume jewelry of modern design4 ,the tumbling process is rather slow1 commonly requiring several days or weeks4 ,however1 little effort is involved on the part of the lapidary1 and1 consequently1 the cost of most tumbled or baroque stones is quite modest4 ,only gem material that is unsuitable for cutting in other manners should be finished in this way4 ,illustration3 ,fig4 #ab4 ,proper placing of the pavilion girdle facets4 ,left3 facets not joined4 ,center3 facets overlapped1 joined too high4 ,right3 correct placing4 ,stone ,dop-wax ,dop-stick ,chuck ,illustration3 ,fig4 #ac4 ,proper sequence of cutting of the crown facets4 ,left to right3 four main facets2 all eight main facets2 half of the crown girdle facets2 completed crown4 ,,texas ,,gemstones ,amber ,composition3 fossil resin4 ,crystal system3 amorphous4 ,hardness3 about #b4j to #b4e4 ,specific gravity3 variable1 from #a4je to #a4aj4 ,luster3 resinous4 ,color3 brown1 yellow1 red1 orange1 and white4 ,streak3 white to yellowish to gray4 ,cleavage3 none4 ,fracture3 conchoidal4 ,tenacity3 brittle4 ,diaphaneity3 transparent to translucent4 ,refractive index3 variable1 about #a4ed4 ,burns with a sweet1 piney odor4 ,rich brown to yellowish amber has been found near ,eagle ,pass1 ,maverick ,county1 in ,cretaceous coal and on ,terlingua ,creek1 ,brewster ,county4 ,although much of this material is translucent and the quality suitable for lapidary purposes1 the pieces are seldom more than a fraction of an inch in diameter4 ,occasional finds of poor quality brownish amber have been reported from the ,tertiary formations of the ,gulf ,coastal ,plain1 but thus far no gem quality material has been found4 ,the softness of amber limits its use to brooches1 necklaces1 and other jewelry that is relatively safe from abrasion4 ,augite ,composition3 ,ca,mg,si,o2 may also contain iron1 aluminum1 and sometimes titanium4 ,crystal system3 monoclinic4 ,hardness3 #e to #f4 ,specific gravity3 #c4b to #c4f4 ,luster3 vitreous to dull4 ,color3 dark greenish brown and greenish black4 ,streak3 light grayish green4 ,cleavage3 two directions1 poor4 ,fracture3 conchoidal to uneven4 ,tenacity3 brittle4 ,diaphaneity3 opaque to translucent4 ,refractive index3 variable1 about #a4fj to #a4ga4 ,augite of gem quality occurs near ,eagle ,flat1 ,hudspeth ,county1 ,texas4 ,although this material is very dark greenish brown and not commonly thought of as a gemstone1 lapidaries have used it to fashion black faceted stones and cabochons that resemble obsidian4 ,most of the augite occurs as loose pieces and crystal fragments that have weathered out of nearby igneous rocks2 the augite can also be found in situ in the igneous rocks4 ,specimens and pieces of cutting quality #a inch in diameter are common1 and fragments over #b inches in diameter have been found4 ,the augite is associated with black spinel and some dark gray to black pieces of natural glass4 ,although the faceted and cabochon-cut stones are not particularly attractive1 some of the larger pieces of augite might be utilized for carving4 ,beryl ,composition3 ,be,al7,si,o74 ,crystal system3 hexagonal4 ,hardness3 #g4e to #h4j4 ,specific gravity3 #b4fc to #b4hj4 ,luster3 vitreous4 ,color3 pale blue1 blue1 green1 yellow1 brownish1 pink1 and colorless4 ,streak3 white4 ,cleavage3 one direction1 very imperfect4 ,fracture3 conchoidal to uneven4 ,tenacity3 brittle4 ,diaphaneity3 transparent to subtranslucent4 ,refractive index3 #a4ef to #a4fj4 ,dispersion3 low4 ,gem-quality beryl has not been reported in ,texas4 ,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 exploration4 ,beryl crystals have been found in pegmatite dikes in ,llano1 ,blanco1 and ,gillespie counties4 ,these crystals are commonly several inches long and exceed #a inch in diameter but are very badly fractured4 ,most of the beryl crystals do not approach gem quality and are entirely unsuitable for any lapidary use4 ,the color of the crystals found thus far is bluish1 greenish1 pinkish brown1 yellowish1 and colorless4 ,some very tiny colorless beryl crystals have been found that are transparent1 but thus far such crystals have been too small to be cut into gems4 ,fine blue beryl crystals have been found in the ,franklin ,mountains near ,el ,paso1 ,texas4 ,unfortunately1 these crystals are so badly flawed and fractured that they are not suitable for lapidary use4 ,it seems likely that careful prospecting of ,texas pegmatites will reveal at least some gem-quality beryl4 ,celestite ,composition3 ,sr,s,o4 ,crystal system3 orthorhombic4 ,hardness3 #c4j to #c4e4 ,specific gravity3 #c4ie to #c4ih4 ,luster3 vitreous4 ,color3 white1 blue1 greenish1 reddish1 and brownish4 ,streak3 white4 ,cleavage3 three directions1 although one of these directions is not easily developed4 ,fracture3 uneven4 ,tenacity3 brittle4 ,diaphaneity3 transparent to subtranslucent4 ,refractive index3 #a4fb to #a4fc4 ,dispersion3 moderate4 ,celestite is very seldom cut into gems4 ,being very soft1 brittle1 and having three cleavages1 celestite is completely unsuitable for jewelry4 ,these same properties make this mineral exceedingly difficult to facet2 however1 faceted stones are seen in large collections4 ,illustration3 ,fig4 #ad4 ,common crystal form of ,travis ,county celestite4 ,same crystal form as shown in ,plate ,i1 ,a4 ,fine crystals of colorless and blue gem-quality celestite 7,pl4 ,i1 ,a1 and fig4 #ad7 have been found at ,mount ,bonnell and other localities west of ,austin1 ,travis ,county4 ,the celestite crystals occur in vugs or geodes in limestone4 ,the crystals are mostly white or colorless and fractured near the base or where attached1 but the tips of the crystals are commonly clear celestine blue and completely free of flaws4 ,crystals several inches in length have been found1 but the average size is about #a inch4 ,the smaller crystals are frequently more transparent and consequently better suited for cutting4 ,it is very difficult to obtain crystals that will allow the cutting of flawless stones of more than #d or #e carats4 ,bluish and colorless celestite of gem quality and fine crystals have been found near ,lampasas1 ,lampasas ,county1 and near ,brownwood1 ,brown ,county1 but neither of these localities has been very productive of good gem material4 ,celestite geodes have been found in parts of ,coke1 ,fisher1 and ,nolan counties1 but these geodes contain little gem material4 ,diamond ,composition3 carbon4 ,crystal system3 isometric4 ,hardness3 #aj4 ,specific gravity3 #c4ea to #c4ec4 ,luster3 adamantine to greasy4 ,color3 brown1 colorless1 pink1 blue1 yellow1 and various other light colors2 rarely deeply colored2 sometimes black4 ,cleavage3 four directions1 octahedral1 perfect4 ,fracture3 conchoidal4 ,tenacity3 brittle4 ,diaphaneity3 transparent to opaque4 ,refractive index3 #b4db4 ,dispersion3 high4 ,there is only one well-authenticated find of diamond in ,texas4 ,a small brownish diamond was found in #aiaa on section #fd1 block #dd1 ,foard ,county 7,sterrett1 #aiab1 pp4 #ajdj-ajda74 ,the exact weight of the stone has not been recorded1 but one authority estimated that it was of sufficient size and clarity to yield a cut stone of about one-quarter carat4 ,the only diamond-bearing rocks known in the ,united ,states are in ,pike ,county1 ,arkansas4 ,although many other diamonds have been found in the ,united ,states1 all were loose in gravels or streams except for some stones at the ,arkansas locality4 ,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 ,state4 ,it is highly unlikely that more than a very few diamonds will ever be found in ,texas1 and any stones that may be found in the future are likely to be widely scattered4 ,epidote ,composition3 ,h,ca7,al1 ,fe7,si,o4 ,crystal system3 monoclinic4 ,hardness3 #f to #g4 ,specific gravity3 #c4be to #c4e4 ,luster3 vitreous4 ,color3 yellowish green to brownish green and brown4 ,streak3 uncolored to grayish4 ,cleavage3 two directions4 ,fracture3 uneven4 ,tenacity3 brittle4 ,diaphaneity3 transparent to opaque4 ,refractive index3 about #a4gb to #a4gg4 ,llano ,county has furnished some green and brownish-green epidote that is suitable for cutting into cabochons4 ,most of the material that approaches gem quality has come from contact metamorphic zones and is associated with garnet1 quartz1 and some scheelite4 ,some small cavities in the rocks contain tiny transparent crystals of gem quality1 but the largest obtainable flawless faceted stones would probably be less than #ae points4 ,faceted stones of epidote are sometimes known as pistacite owing to their common pistachio-green color4 ,fluorite ,composition3 ,ca,f4 ,crystal system3 isometric4 ,hardness3 #d4 ,specific gravity3 #c4j to #c4be4 ,luster3 vitreous4 ,color3 violet1 blue1 colorless1 green1 yellow1 brown1 rose1 and crimson red4 ,streak3 white4 ,cleavage3 four directions1 octahedral1 perfect4 ,fracture3 subconchoidal to splintery4 ,tenacity3 brittle4 ,diaphaneity3 transparent to subtranslucent4 ,refractive index3 #a4dcd4 ,very fine green1 transparent fluorite has been found near ,voca1 ,mason ,county4 ,the fluorite occurs as vug fillings in pegmatites1 associated with crystals of pink microcline and colorless quartz4 ,most of the vugs have been completely filled by the fluorite2 therefore1 crystals 7fig4 #ae7 of the fluorite are not too common4 ,masses of fluorite several pounds in weight1 rich green1 and quite transparent have been found near ,voca4 ,transparent pieces an inch or more in diameter are common4 ,illustration3 ,fig4 #ae4 ,common crystal form of fluorite4 ,fluorite is much too soft for everyday use in jewelry and because of the low refractive index does not yield brilliant faceted stones4 ,the perfect four-directional cleavage1 relative softness1 and brittle tenacity of the mineral make it difficult to facet4 ,faceted stones are seldom seen outside of collections4 ,cabochons are also difficult to cut from this material1 but the rich color obtained is ample reward for the time and care necessary in cutting4 ,fluorite occurs at several other localities in ,texas1 notably in ,hudspeth1 ,brewster1 ,presidio1 ,llano1 and ,burnet counties1 but not commonly in gem quality or colors that warrant its use as gem material4 ,fossil ,wood ,wood that is buried in silica-rich sediments is commonly replaced by quartz1 agate1 or opal4 ,the wood structure1 including a large number of the annular rings1 knots1 small branches1 and bark1 may be preserved4 ,this process of replacement by silica is believed to take considerable time4 ,preservations by other means 7see ,jet1 p4 #bb7 are known1 but silica replacements are most commonly used as gem materials4 ,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 attractively4 ,excellent gem-quality fossil wood 7,pl4 ,i1 ,b7 has been found at a great number of localities in ,texas4 ,agatized and opalized wood occurs in great abundance along the outcrops of ,eocene and ,oligocene strata of the ,texas ,gulf ,coastal ,plain4 ,much of this material is very well suited for cabochons1 bookends1 and other lapidary uses4 ,the preservation is especially good at numerous localities in ,washington1 ,lee1 ,fayette1 and ,gonzales counties1 and the variety of colors1 such as bluish1 gray1 brown1 red1 yellow1 and black1 makes this material especially sought after by 8rock-hounds40 ,some of the agatized and opalized wood fluoresces yellow or green under ultra-violet light4 ,the fossil wood is sometimes found as stumps1 limb sections1 or large trunk fragments1 but the great majority of the gem material is found as small broken fragments or stream-rolled cobbles4 ,fossil palm wood is by far the most sought after variety because this material displays 8eyes0 and tube-like structures that yield very attractive cabochons and cabinet specimens4 ,texas fossil palm wood is highly regarded by cutters from all parts of the country1 and this material is thought by many lapidaries to be some of the finest gem-quality fossil wood in the ,united ,states4 ,gravel pits and river gravels in ,live ,oak ,county have produced very fine agatized wood4 ,although the gem material does not seem to be as abundant in this area as it is in counties to the northeast1 the vivid colors and excellent preservation of the fossil wood in ,live ,oak ,county have attracted collectors from all over the ,state4 ,the fossil wood usually occurs as large rounded cobbles in the streams4 ,much of this material is quite translucent when cut and contains various shades of brown1 orange1 and red4 ,the gravels of the ,rio ,grande have produced some fossil wood in addition to the excellent agate that is also found there4 ,most of the fossil wood found in these gravels is very well preserved1 but the colors are commonly dull shades of brown4 ,occasional fine red and yellow specimens have been recovered from the ,rio ,grande gravels1 but these are rare4 ,good agatized wood has been found in and near ,palo ,duro ,canyon1 ,armstrong ,county1 about #ej miles southeast of ,amarillo4 ,large trunk sections are not uncommon1 but most of the material of cutting quality is obtained from small fragments4 ,the ,palo ,duro ,canyon fossil wood greatly resembles the famous ,arizona ,petrified ,forest wood but is not nearly as plentiful4 ,the ,palo ,duro wood contains yellow1 brown1 red1 and bluish colors most commonly4 ,some of the wood-producing area is within ,palo ,duro ,canyon ,state ,park which is1 of course1 closed to collecting4 ,the surrounding area has been worked diligently by local collectors1 but new pieces of wood are exposed after heavy rains4 ,webb and ,duval counties have also produced some good fossil wood specimens4 ,gadolinite ,composition3 ,be,fe,y,si,o4 7,various other rare-earth elements may substitute into this mineral structure47 ,crystal system3 monoclinic4 ,hardness3 #f4e to #g4j4 ,specific gravity3 about #d4b4 ,luster3 vitreous to greasy4 ,color3 black2 in thin splinters dark bottle green4 ,streak3 white to greenish4 ,cleavage3 none4 ,fracture3 conchoidal to splintery4 ,tenacity3 brittle4 ,diaphaneity3 opaque to subtransparent in thin pieces4 ,refractive index3 variable1 about #a4gg to #a4hb4 ,gadolinite as a cut gem is not seen outside of large collections2 however1 it can be faceted into black opaque stones of little beauty but of great interest to collectors4 ,the best known locality of this mineral in the ,united ,states is ,baringer ,hill1 ,llano ,county1 ,texas4 ,unfortunately1 this locality was completely flooded by the completion of ,buchanan ,dam in #aich4 ,masses and rough crystals of gadolinite weighing over #ajj pounds were mined from this locality4 ,the gadolinite occurred in a large1 very coarse-grained pegmatite dike associated with quartz1 microcline1 and fluorite1 as well as allanite1 fergusonite1 nivenite1 cyrtolite1 thorogummite1 and various other rare minerals4 ,some of the minerals in the dike occurred in very large masses4 ,one quartz mass over #dj feet in diameter was noted1 and microcline masses up to #cj feet in diameter were not uncommon4 ,much of the gadolinite was used by industrial firms as a source of thorium compounds1 although some specimen and gem material found its way into museums and private collections4 ,because the locality was worked mostly from #aiaj to about #aibe and because since #aich the waters of ,lake ,buchanan have completely flooded the entire area1 material from this locality is now exceedingly difficult to obtain4 ,the collection of the ,smithsonian ,institution1 ,washington1 ,d4,c41 contains a cut and polished gem of ,baringer ,hill gadolinite that weighs #h4f carats4 ,this mineral is radioactive because of the presence of uranium1 thorium1 and other rare radioactive elements4 ,garnet ,the garnet group of minerals is variable in composition4 ,listed below are the pure members of this group1 but garnets found in nature are usually a mixture of two or more of these end members4 ,aluminum garnet-- ,grossularite 7calcium-aluminum garnet71 ,ca,al7,si,o7 ,pyrope 7magnesium-aluminum garnet71 ,mg,al7,si,o7 ,almandite 7iron-aluminum garnet71 ,fe,al7,si,o7 ,spessartite 7manganese-aluminum garnet71 ,mn,al7,si,o7 ,iron garnet-- ,andradite 7calcium-iron garnet71 ,ca,fe7,si,o72 may contain magnesium1 titanium1 and yttrium ,chromium garnet-- ,uvarovite 7calcium-chromium garnet71 ,ca,cr7,si,o7 ,since almandite is the only variety of garnet known to occur commonly in gem quality in ,texas1 the following properties are for almandite except where noted4 ,crystal system3 isometric 7all varieties74 ,hardness3 about #g4e4 ,specific gravity3 #d4be4 ,luster3 vitreous to resinous4 ,color3 red1 deep red1 and brownish red 7other varieties also yellow1 white1 orange1 pink1 black1 and green74 ,streak3 white4 ,cleavage3 none4 ,fracture3 subconchoidal to uneven4 ,tenacity3 brittle to tough4 ,diaphaneity3 transparent to subtranslucent4 ,refractive index3 about #a4hc4 ,good crystals of gem-quality almandite garnet have been found in ,llano1 ,blanco1 ,burnet1 and ,gillespie counties4 ,in southeast ,llano ,county1 northwest ,blanco ,county1 and northeast ,gillespie ,county1 the stones mostly occur in stream gravels where they have collected after being weathered out of compact mica schists4 ,owing to the fact that most of the garnets have not been transported very far from their source1 the stones commonly show good crystal form 7,pl4 ,,ii1 ,a74 ,all of the garnets from one locality commonly do not have exactly the same crystal form4 ,the garnets are mostly widely scattered in the stream gravels but can be found concentrated behind rocks and on small gravel bars4 ,many of the crystals are less than one-eighth inch in diameter2 however1 good crystals one-fourth to one-half inch in diameter are common4 ,most of the stones are too fractured or have too many inclusions to yield gems1 but many transparent stones have been found4 ,the transparent crystals usually yield flawless deep red faceted stones of #b carats or less4 ,some of the stones that contain too many inclusions to facet are cut as cabochons and are then often known as carbuncle4 ,small garnet fragments have been found in streams and in gneisses and pegmatites near ,castell1 ,llano ,county1 but they are not commonly of gem quality4 ,occasional small gem-quality garnets have been found in pegmatites and contact metamorphic zones in ,burnet ,county4 ,garnets have also been found in several other counties1 notably ,mason1 ,el ,paso1 ,hudspeth1 and ,culberson1 but no stones of facet quality have been reported4 ,jet ,composition3 a variety of brown coal or lignite4 ,structure3 woody4 ,hardness3 #c to #d4 ,specific gravity3 about #a4cj to #a4ce4 ,luster3 dull4 ,color3 black1 brownish black4 ,streak3 brown to brownish black4 ,cleavage3 none4 ,fracture3 uneven to smooth4 ,tenacity3 tough to slightly brittle4 ,diaphaneity3 opaque4 ,burns with a sooty yellowish flame4 ,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 structure4 ,the best specimens of jet polish into lustrous black cabochons4 ,jet occurs in ,presidio ,county as compressed and flattened trunks of trees in a thin layer of coal and lignite in ,cretaceous strata #ajj to #bjj feet stratigraphically below the ,san ,carlos beds4 ,specimens of 8jet0 have been found in some of the lignitic ,tertiary strata of the ,texas ,gulf ,coastal ,plain2 however1 this material is mostly soft1 brownish1 and not of gem quality4 ,labradorite ,composition3 ,na,al,si,o1 #ej to #cj2 ,ca,al,si,o1 #ej to #gj4 ,crystal system3 triclinic4 ,hardness3 #f4j to #f4e4 ,specific gravity3 about #b4fj4 ,luster3 vitreous to sometimes pearly4 ,color3 straw yellow1 white1 greenish1 gray1 reddish1 bluish1 and green4 ,sometimes shows a play of colors on particular cleavage surfaces4 ,streak3 uncolored4 ,cleavage3 three directions4 ,fracture3 uneven to conchoidal4 ,tenacity3 brittle4 ,diaphaneity3 transparent to translucent4 ,refractive index3 about #a4ef4 ,dispersion3 low4 ,very fine facet-quality labradorite has been found about #bj miles south of ,alpine1 ,brewster ,county4 ,the labradorite occurs loose in the soil as slightly weathered or frosted cleavage fragments1 commonly showing one or more crystal faces 7,pl4 ,,ii1 ,b74 ,the pale-yellow or straw-yellow color of these fragments1 as well as their lack of internal imperfections1 makes these stones excellent gem material4 ,individual pieces that exceed three-fourths inch in their longest dimensions are rare4 ,cut stones of more than #e or #f carats from this locality are scarce4 ,the source of this material is uncertain1 but it is probably weathering out of an underlying igneous rock4 ,microcline ,composition3 ,k,al,si,o4 ,crystal system3 triclinic4 ,hardness3 #f4j to #f4e4 ,specific gravity3 #b4ed to #b4eg4 ,luster3 vitreous to pearly4 ,color3 white1 pale yellow1 red1 blue green1 bluish4 ,streak3 white4 ,cleavage3 four directions1 usually three of these distinct4 ,fracture3 uneven4 ,tenacity3 brittle ,diaphaneity3 transparent to translucent4 ,refractive index3 about #a4eb to #a4ec4 ,very fine crystals of blue microcline have been found east of ,packsaddle ,mountain and near ,kingsland in ,llano ,county4 ,crystals exceeding #a foot in length have been found1 although most are only a few inches long4 ,the color of the microcline is mostly pale blue1 but some crystals are darker4 ,microcline crystals associated with milky or vein quartz1 smoky quartz1 some biotite1 and rarely cassiterite occur in pegmatite dikes which vary in size from a few inches to several feet in thickness4 ,the color of this microcline is pale in comparison to microcline from some other localities in the ,united ,states1 but the ,texas blue microcline does yield pleasing cabochons4 ,perfect crystals of this material are prized by collectors4 ,blue or greenish microcline is often called amazonite or amazon stone4 ,bluish microcline associated with quartz and topaz has also been reported near ,katemcy1 ,mason ,county4 ,red microcline is common in several central ,texas counties and is a primary constituent of many of the igneous rocks in those counties4 ,large crystals of perthitic red microcline occur in pegmatite dikes of ,mason1 ,llano1 ,burnet1 and ,gillespie counties4 ,any feldspar quarry or other pegmatite mining operation in any of these counties is likely to contain large red microcline crystals and fragments4 ,unfortunately1 the good crystals that may have been present are often shattered by blasting during quarrying operations4 ,feldspar quarries in northeastern ,gillespie ,county have yielded some good red cabochon material as well as good crystals4 ,here the microcline occurs with milky and smoky vein quartz1 smoky quartz crystals1 clear quartz crystals1 greenish muscovite1 and biotite4 ,many of the older quarries in ,gillespie ,county have not been active for some time1 and the dumps and quarry walls have been diligently searched by collectors4 ,illustration3 ,fig4 #af4 ,crystal faces on microcline specimen shown in ,plate ,,iii1 ,a4 ,many of the pegmatite dikes near ,lake ,buchanan in ,llano and ,burnet counties have produced some good red microcline specimens and cutting material 7,pl4 ,,iii1 ,a1 and fig4 #af74 ,many of these crystals are more pinkish than those in ,gillespie ,county1 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 crystals4 ,numerous other local areas in the counties mentioned1 as well as some localities in ,hudspeth and ,culberson counties1 have also produced small amounts of red and pink microcline of gem quality4 ,obsidian ,composition3 volcanic glass4 ,structure3 amorphous4 ,hardness3 #e4j to #e4e4 ,specific gravity3 #b4c to #b4e4 ,luster3 vitreous4 ,color3 black1 dark gray1 reddish1 brown1 bluish1 and greenish4 ,streak3 white4 ,cleavage3 none4 ,fracture3 conchoidal4 ,tenacity3 brittle4 ,diaphaneity3 translucent to nearly opaque4 ,refractive index3 variable1 about #a4de to #a4ec4 ,gem-quality black and dark-gray obsidian has been found in ,presidio ,county associated with extrusive igneous rocks4 ,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 cabochons4 ,some of the small weathered pieces of this material resemble tektite in outward appearance2 in fact1 the 8valverdites0 mistaken originally for tektites are pebbles of weathered obsidian in terrace gravel of ,val ,verde ,county4 ,obsidian takes a high polish but is very sensitive to heat4 ,stones that are slightly overheated during grinding or sanding will quickly shatter4 ,obsidian of gem quality has been reported also in ,brewster ,county4 ,opal ,composition3 ,si,on,h,o4 ,structure3 amorphous4 ,hardness3 #e4e to #f4e4 ,specific gravity3 #a4i to #b4c4 ,luster3 subvitreous to pearly4 ,color3 white1 bluish1 pink1 brown1 yellow1 and gray4 ,streak3 white4 ,cleavage3 none4 ,fracture3 conchoidal4 ,tenacity3 brittle4 ,diaphaneity3 transparent to nearly opaque4 ,refractive index3 #a4dc4 ,opal other than as fossil or opalized wood 7pp4 #bj-ba7 occurs at the following several localities in ,texas4 ,approximately #af miles south of ,alpine1 ,brewster ,county1 precious opal occurs in very small seams and as cavity fillings in very hard pinkish-brown rhyolite4 ,this opal is milky or bluish and commonly exhibits small flashes of blue1 green1 red1 and orange fire4 ,individual pieces of this opal are mostly quite small1 rarely over one-fourth inch in diameter1 and very difficult to remove from the tough rhyolite matrix4 ,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 cabochon4 ,small finds of opal associated with rhyolites and basalts have come from other localities in west ,texas1 but the opal mostly does not display enough play of colors to warrant its use as gem material4 ,near ,freer1 ,duval ,county1 some very attractive common opal has been found4 ,the opal is colored various shades of pink1 blue1 and yellow and in certain local areas occurs as fragments that are cemented together by clear chalcedony4 ,various colors are commonly found in the same piece1 and such material yields handsome cabochons4 ,although the area has never been worked commercially1 it has been hunted by collectors and cutters for several years4 ,pearl ,pearls are the result of the secretion of calcium carbonate by various shellfish around sand grains1 parasitic organisms1 shell fragments1 or other foreign objects that have in some way entered the body cavity of the shellfish4 ,since the shellfish is unable to expel these irritating particles or organisms1 it deposits successive layers of calcium carbonate around the foreign substance to make it smoother and less irritating4 ,although pearls are principally calcium carbonate1 they also contain small amounts of an organic substance1 called conchiolin1 and water4 ,pearls are found in shellfish that live in either fresh or salt water4 ,few pearls are spherical in shape2 most are rounded but somewhat irregular and are known as baroque pearls4 ,good quality pearls are the only gemstone commonly sold by the grain1 a unit of weight equal to #j4be carat or #j4je gram4 ,the pearl grain is not the same unit of weight as the ,troy grain4 ,in ,texas1 pearls have been found in fresh-water clams in most of the major rivers and streams1 notably in the ,brazos1 ,concho1 ,colorado1 ,guadalupe1 ,llano1 ,nueces1 ,sabine1 ,rio ,grande1 and ,trinity ,rivers4 ,several ,texas lakes have also yielded pearls1 notably ,caddo ,lake and other lakes in north-central and northeast ,texas4 ,small pearls are frequently found along the ,texas ,gulf ,coast in edible oysters and other common shellfish4 ,fossil pearls have also been found but because of their darkened appearance are of value only as curiosities4 ,the pearls thus far found in ,texas have been of relatively poor quality and show little or no iridescence4 ,these pearls have little value except as curiosities1 although one writer has stated that the discovery of pearls in the ,nueces ,river led to the original ,spanish settlement of the ,state 7,baker1 #aice1 p4 #efi74 ,quartz ,composition3 ,si,o4 ,crystal system3 hexagonal4 ,hardness3 #g4 ,specific gravity3 #b4fe to #b4ff in crystals4 ,luster3 vitreous1 also waxy1 greasy1 and dull4 ,color3 most often colorless1 brown1 yellow1 violet2 sometimes green1 red1 blue1 and black2 cryptocrystalline varieties often variously colored by impurities4 ,streak3 white4 ,cleavage3 indistinct4 ,fracture3 conchoidal to splintery4 ,tenacity3 brittle to tough4 ,diaphaneity3 transparent to opaque4 ,refractive index3 #a4edd to #a4eec4 ,the quartz family gemstones can be divided into two groups for purposes of description4 ,the first group is the crystalline varieties1 or those quartz varieties that commonly occur in distinct crystals4 ,the second group is the cryptocrystalline varieties1 or those quartz varieties that occur as irregular masses that are composed of many microscopic crystals4 ,the crystalline varieties are usually much more transparent and are most often seen as faceted stones4 ,the cryptocrystalline varieties vary from subtransparent to opaque and are almost always cut as cabochons4 ,,crystalline ,,varieties ,amethyst 7violet to purple-colored quartz74--,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 talc4 ,many crystals have been found loose in the soil4 ,the amethyst tends to be very irregularly colored in zones parallel to the crystal faces4 ,in many1 the base of the crystal is colorless or white and only the termination is violet4 ,crystals up to #c inches long have been found at this locality1 but the average size is much less4 ,the surface at this locality is almost entirely depleted of amethyst1 with only an occasional small crystal or fragment to be seen4 ,however1 small excavations are still sometimes productive4 ,good groups of pale amethyst crystals have been found in quartz veins near the old town site of ,oxford1 ,llano ,county4 ,the occurrence seems to be much the same as the ,amethyst ,hill locality4 ,little exploration for gemstones has been done in this area1 and future discoveries seem likely4 ,chalcedony geodes lined with amethyst crystals have been found in ,brewster1 ,presidio1 ,culberson1 and ,hudspeth counties1 but the occurrences are scattered4 ,the crystals are seldom large enough to yield gems of more than #c carats and are mostly very light colored4 ,a few pieces of gem-quality amethyst have been found in ,burnet ,county4 ,citrine 7yellow quartz74--,very little gem-quality citrine has been reported in ,texas4 ,some small citrine crystals have been found at ,amethyst ,hill in northeastern ,gillespie ,county1 but few are of sufficient size or color to yield good gems4 ,the writer has seen one citrine crystal that was found in the gravels of a small stream in eastern ,llano ,county near ,buchanan ,dam4 ,the crystal weighs about #a ounce and is perfectly clear1 light golden yellow1 and flawless4 ,however1 a further search of the stream gravels failed to produce any other citrines4 ,rock crystal 7colorless quartz74--,numerous localities in ,texas produce this colorless variety of quartz1 which is the most common variety of facet quality quartz and consequently is of little value4 ,rock crystal occurs at many localities in ,burnet1 ,llano1 and ,mason counties4 ,the crystals mostly occur in pegmatite dikes or in stream gravels where they have been weathered out of their parent rock4 ,some fine colorless quartz crystals have been found near ,voca1 ,mason ,county1 in weathered pegmatite dikes and also loose in the sands of nearby streams4 ,crystals from this locality are often stained with reddish iron oxide on their outer surfaces4 ,some of the rock crystal found near ,katemcy1 ,mason ,county1 shows asterism when cut with the proper orientation4 ,fine clear colorless crystals up to #h inches long have been found in the pegmatite dikes near ,lake ,buchanan in both ,llano and ,burnet counties4 ,several localities near ,enchanted ,rock in ,llano ,county have also produced some good colorless crystals4 ,feldspar quarries in large pegmatites in northeastern ,gillespie ,county have yielded attractive quartz crystals1 some of which contain smoky phantom crystals and tourmaline inclusions4 ,some pieces of rock crystal enclosing green1 needle-like actinolite crystals have been found near the ,llano-,gillespie-,blanco ,county corner4 ,this material is not suitable for faceted gems but does lend itself to interesting and attractive cabochons4 ,colorless quartz crystals commonly are found lining small chalcedony geodes in ,brewster1 ,presidio1 ,culberson1 ,hudspeth1 ,reeves1 and ,jeff ,davis counties4 ,these crystals are most commonly less than #a inch long but are mostly very clear4 ,rock crystal has been found in crevices of petrified wood in many east and southeast ,texas counties1 although the crystals are mostly quite small4 ,many lesser occurrences of rock crystal1 too numerous to mention1 are located within the ,state4 ,rose quartz 7pink quartz74--,rose quartz occurs at various localities in ,burnet1 ,llano1 ,mason1 and ,gillespie counties1 but the amount of material is mostly small and the greater part unsuitable for gem purposes4 ,some good pink rose quartz occurs near ,town ,mountain1 ,llano ,county1 but this material does not have flawless areas large enough to yield faceted stones of more than a few carats4 ,rose quartz is always slightly milky1 or cloudy1 and does not cut into brilliant faceted stones4 ,the ,town ,mountain rose quartz has been cut into attractive cabochons4 ,smoky quartz 7brown1 yellow-brown1 and golden-brown quartz74--,several ,texas localities have produced fine smoky quartz4 ,baringer ,hill1 a noted rare-earth minerals pegmatite locality in ,llano ,county1 contained some smoky quartz crystals that were estimated to weigh over #a1jjj pounds1 and the locality produced many smaller crystals that were of gem quality4 ,baringer ,hill was flooded by the completion of ,buchanan ,dam in #aich and is presently under the waters of ,lake ,buchanan4 ,a few fine golden-brown gem-quality crystals have been found along the lake shore and in small pegmatites nearby 7,pl4 ,,iii1 ,b474 ,feldspar quarries in northeastern ,gillespie ,county have produced smoky quartz crystals that exceed #a foot in length1 but these crystals are mostly flawed1 possibly as a result of blasting1 and mostly contain only small clear areas4 ,good color smoky quartz crystals are found with topaz in the pegmatites and stream beds in ,mason ,county1 near ,streeter1 ,grit1 and ,katemcy4 ,these crystals tend to be lighter colored than those near ,lake ,buchanan1 but they commonly contain large flawless areas4 ,,cryptocrystalline ,,varieties ,chalcedony4--,when free from impurities of various oxides and other compounds1 chalcedony has little to render it pleasing as a gemstone4 ,it is mostly gray1 white1 brown1 or bluish and commonly has a waxy luster4 ,some of the chalcedony found along the ,rio ,grande ,valley and in west ,texas will take dyes1 and local lapidaries have had some success in dyeing this material various shades of blue1 green1 yellow1 and red4 ,when the chalcedony is naturally colored and variegated1 usually in bands1 mossy figures1 or dendritic forms1 it is called agate4 ,agate 7variegated chalcedony74--,the wide variety of markings and colors available together with the ease of cutting make agate a favorite of many lapidaries4 ,fine agate has been found at numerous localities in west and south ,texas4 ,fine plume agate1 famous throughout the ,united ,states1 is found south of ,alpine4 ,plume agate is characterized by dendritic or tree-like inclusions and is mostly cut into very handsome cabochons4 ,the agate from south of ,alpine commonly contains black1 red1 yellow1 or brown plumes within the same piece4 ,the variety of colors and lack of porosity of this agate make it highly desired among lapidaries4 ,the agate occurs loose on the surface of the ground and in the soil in small nodules that have a very rough1 brownish surface4 ,these nodules are mostly less than #c inches in diameter1 although specimens of gem quality have been found that exceed #bjj pounds4 ,some very fine agate has been found in the vicinity of ,needle ,peak1 ,presidio ,county4 ,this material is mostly green moss agate in clear chalcedony and commonly contains small yellow 8sun-burst0 figures4 ,the contrasting yellow and green design makes very beautiful cabochons4 ,fine agate has been found south of ,marfa1 ,presidio ,county4 ,this agate is mostly clear chalcedony with black1 yellow1 or variously colored plumes1 moss1 or 8bouquet-like0 figures4 ,numerous other localities in ,presidio and ,brewster counties have produced good agate4 ,various amounts of agate1 jasper1 and chalcedony occur in the gravels of the ,rio ,grande in varying quantities from ,big ,bend ,national ,park downstream to ,brownsville4 ,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 ,grande4 ,the greatest concentration of agate and related gem materials seems to be in the area between ,laredo and ,rio ,grande ,city4 ,vast quantities of excellent gem material have been removed from this area for many years 7,pl4 ,,iv74 ,the agate occurs as rounded1 stream-worn cobbles and commonly has a thin white coating that makes it difficult to distinguish from the abundant chert and other rocks4 ,the agate occurs in cobbles that are mostly #c to #f inches in diameter1 but specimens of gem quality that exceed twice this size are known4 ,the agate varies greatly in design and color4 ,plume1 moss1 banded1 and sagenitic agate occur in these gravels in a wide variety of colors4 ,the jasper in the ,rio ,grande gravels is yellow1 red1 green1 or various shades of these and is commonly suspended as angular fragments in clear chalcedony4 ,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 localities4 ,agatized wood 7see ,fossil wood1 pp4 #bj-ba74 ,carnelian 7translucent reddish chalcedony74--,this variety of chalcedony in small quantities has been reported from near ,van ,horn1 ,hudspeth ,county4 ,small pieces of carnelian have been found in the gravels of the ,rio ,grande1 but finds have been few and scattered4 ,jasper 7impure opaque or subtranslucent quartz74--,good green1 yellow1 red1 and brown jasper has been found in the gravels of the ,rio ,grande at all of the localities that produce agate4 ,the colors are quite vivid1 and the material takes a fine polish4 ,some pieces of orbicular jasper 7jasper with circular or eye-like markings7 have been found in this material4 ,these gravels commonly contain jasper as fragments that are suspended in clear chalcedony2 this is called brecciated jasper and yields very handsome cabochons4 ,many of the west ,texas agate localities also produce jasper in quantity4 ,good jasper has been reported from north of ,brackettville1 ,kinney ,county4 ,jasper is a minor constituent of the stream gravels in many parts of the ,state4 ,sanidine ,composition3 ,k,al,si,o2 commonly contains some sodium4 ,crystal system3 monoclinic4 ,hardness3 #f4 ,specific gravity3 #b4eg to #b4eh4 ,luster3 vitreous to pearly4 ,color3 colorless1 white1 pale yellow1 and gray4 ,streak3 uncolored4 ,cleavage3 three directions4 ,fracture3 conchoidal to uneven4 ,tenacity3 brittle4 ,diaphaneity3 transparent to subtranslucent4 ,refractive index3 #a4eb to #a4ec4 ,some feldspars1 including sanidine1 show a nice blue sheen in reflected light parallel to certain crystallographic directions4 ,stones having this property are called moonstone4 ,a clear yellowish sanidine showing an attractive blue sheen has been found in ,brewster1 ,jeff ,davis1 and ,presidio counties4 ,the individual pieces are small1 the average size being about one-eighth inch4 ,the sanidine is found loose in the soil at some localities where it has weathered out of rhyolite1 and specimens of the sanidine in the parent rock are not difficult to obtain4 ,very small cabochons can be cut from this material1 but few lapidaries have done so because inexpensive larger pieces of moonstone can be obtained easily from foreign sources4 ,however1 the west ,texas sanidine does show a blue sheen when cut and polished4 ,spinel ,composition3 ,mg,al,o 7magnesium may be replaced in part by ferrous iron or manganese and the aluminum by ferric iron and chromium74 ,crystal system3 isometric4 ,hardness3 #h4 ,specific gravity3 #c4e to #d4a4 ,luster3 vitreous to sub-metallic4 ,color3 black1 pink1 red1 blue1 green1 yellow1 brown1 and violet4 ,streak3 white4 ,cleavage3 one direction1 imperfect4 ,fracture3 conchoidal4 ,tenacity3 brittle4 ,diaphaneity3 transparent to opaque4 ,refractive index3 variable1 approximately #a4gb to #b4jj4 ,in many areas of the world1 fine quality1 beautifully colored1 transparent spinels are found and used as gems4 ,the only gem-quality spinel reported thus far in ,texas is black and opaque4 ,near ,eagle ,flat in ,hudspeth ,county1 black spinel crystals have been found associated with augite and natural glass2 these minerals are weathering out of an intrusive igneous rock4 ,the spinel crystals have an octahedral form which is common for this mineral 7fig4 #ag74 ,most of the spinels are free of flaws1 but because of their black color they have little value as gems4 ,the crystals are found loose in the sand of streams near the outcrops of the igneous rock or embedded in the rock4 ,they seldom exceed half an inch in diameter4 ,these stones are primarily sought by collectors4 ,illustration3 ,fig4 #ag4 ,common crystal form of spinel4 ,tektite 7,bediasite7 ,composition3 ,a natural glass1 approximately #ge ,si,o1 #ae ,al,o1 #d ,fe,o1 also ,mg,o1 ,na,o1 ,k,o1 and traces of other elements4 ,crystal structure3 amorphous4 ,hardness3 #e to #f4 ,specific gravity3 #b4cc to #b4dd4 ,luster3 vitreous1 often dull on weathered surfaces4 ,color3 dark brown1 greenish brown1 appears black in thick sections4 ,streak3 uncolored4 ,cleavage3 none4 ,fracture3 conchoidal4 ,tenacity3 brittle4 ,diaphaneity3 transparent to subtransparent4 ,refractive index3 #a4dhh to #a4eab4 ,the average bediasite size is about #a inch in diameter1 although specimens approximately #c inches in diameter are known4 ,the uncut tektites are very interesting1 showing a variety of shapes and surface features 7,pl4 ,v1 ,a7 and many exhibit contorted flow structure4 ,the surface of many tektites is grooved or furrowed1 while on others it is smooth or frosted4 ,the ,texas tektites are known as 8bediasites10 after place names in ,grimes ,county traceable to the ,bedias ,indians who formerly lived there4 ,dark brown and greenish-brown tektites have been found in ,texas in gravels at scattered localities in ,walker1 ,grimes1 ,brazos1 ,burleson1 ,lee1 ,fayette1 ,gonzales1 ,lavaca1 and ,de,witt counties4 ,outside of ,texas the only other authenticated tektite localities in the ,united ,states at the present time are in ,dodge and ,irwin counties1 ,georgia4 ,a fragment of a similar tektite has recently been reported from near ,martha's ,vineyard1 ,massachusetts4 ,the tektites reported from ,oklahoma are now known to be pebbles of obsidian4 ,although tektites have little value or beauty as gemstones1 they have been cut by lapidaries as both faceted and cabochon stones4 ,tektites take a high polish but are mostly so dark in color that they appear black4 ,the origin of tektites is of great scientific interest and is currently the subject of much debate4 ,some scientists believe that tektites are of meteoritic origin1 while others believe that tektites were formed by various terrestrial processes4 ,since no one has actually observed a tektite to fall or form1 and many of the theories of origin are difficult to prove without direct observation1 the origin of tektites is likely to remain in controversy for some time4 ,topaz ,composition3 ,al7,f1 ,,oh7,si,o4 ,crystal system3 orthorhombic4 ,hardness3 #h4 ,specific gravity3 #c4d to #c4f4 ,luster3 vitreous4 ,color3 pale blue1 sky blue1 greenish1 white1 wine yellow1 straw yellow1 grayish1 pink1 reddish1 and orange4 ,streak3 uncolored4 ,cleavage3 one direction1 basal1 highly perfect4 ,fracture3 conchoidal to uneven4 ,tenacity3 brittle4 ,diaphaneity3 transparent to subtranslucent4 ,refractive index3 about #a4fj to #a4fc4 ,dispersion3 moderate4 ,various yellow and smoky colored quartz gems are offered for sale as 8,spanish ,topaz10 8,smoky ,topaz10 8,madeira ,topaz10 and 8,topaz ,quartz40 ,these names are entirely misleading and should be dropped from usage4 ,fine gem-quality white1 pale-blue1 and sky-blue topaz has been found near ,streeter1 ,grit1 and ,katemcy1 ,mason ,county4 ,this ,texas gem material compares favorably in color1 size1 and clarity with topaz found anywhere in the ,united ,states4 ,fine crystals of topaz 7,pl4 ,v1 ,b1 and fig4 #ah7 occasionally are found in pegmatite dikes associated with quartz1 black tourmaline1 cassiterite1 and pink microcline4 ,many of the gem-bearing pegmatites have been eroded away1 leaving the topaz concentrated in the stream beds4 ,the stones mostly occur as frosted1 stream-worn pebbles 7,pl4 ,,vi1 ,a7 in the numerous small creeks in the area4 ,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 bed4 ,the stones tend to lodge behind boulders or small dikes cutting across the stream4 ,illustration3 ,fig4 #ah4 ,crystal faces on topaz crystal shown in ,plate ,v1 ,b4 ,this crystal habit is typical of the topaz from ,mason ,county4 ,the white or colorless stones are by far the most common1 outnumbering the bluish stones about ten to one4 ,the color of the blue stones tends to be irregularly distributed in zones parallel to the crystal faces4 ,topaz that is colored in this manner should be cut with the best blue color near the bottom or culet of the gem 7fig4 #ai74 ,if done correctly1 this will give the entire gemstone the desirable blue color4 ,illustration3 ,fig4 #ai4 ,cross section showing the proper orientation of dark-color zone in a gem cut from an irregularly colored stone4 ,,colorless ,,blue ,the colorless stones can be turned pale yellow1 yellowish brown1 or straw yellow by exposure to ,x-ray radiation1 and some of the bluish stones will fluoresce faintly yellowish under ultra-violet light4 ,the largest gem-quality topaz crystal yet found in ,north ,america has come from ,mason ,county4 ,it is a pale-blue crystal weighing #a1bif grams1 now in the collection of the ,u4,s4 ,national ,museum4 ,several other large pieces1 some weighing over a pound1 have been found4 ,one large crystal1 exact weight unknown1 was found near ,katemcy4 ,several gem cutters have estimated that this stone could easily yield a single1 flawless pale-blue gem of about #ejj carats4 ,many large gems have been cut from topaz found in this area1 including at least one stone of over #cjj carats4 ,one obstacle in the cutting of topaz is its perfect basal cleavage4 ,the gemstone should be oriented so that no facet of the stone will be parallel to or within less than about #e degrees of the cleavage direction1 or the facet may be very difficult or impossible to polish4 ,it is difficult to estimate the productivity of this area since its discovery in the early #aijj's4 ,few systematic attempts have been made to exploit the deposits1 and a great amount of the topaz thus far recovered has been found by private collectors4 ,the ,mason ,county topaz deposits are still very productive1 and additional exploration may uncover even more gem-producing areas4 ,topaz has also been found in stream gravels or pegmatites in ,burnet1 ,llano1 ,gillespie1 and ,el ,paso counties but very rarely in gem quality4 ,tourmaline ,composition3 ,h,al7,b,,oh7,si,o2 hydrogen often replaced by iron1 magnesium1 calcium1 or fluorine4 ,crystal system3 hexagonal4 ,hardness3 #g to #g4e4 ,specific gravity3 #b4ih to #c4bj4 ,luster3 vitreous to resinous4 ,color3 black1 brownish black1 brown1 blue1 green1 red1 pink1 yellow1 and gray4 ,streak3 uncolored4 ,cleavage3 two directions1 very imperfect4 ,fracture3 subconchoidal to uneven4 ,tenacity3 brittle4 ,diaphaneity3 transparent to opaque4 ,refractive index3 about #a4fb to #a4fd4 ,black tourmaline is schorl2 brown tourmaline1 dravite4 ,good crystals of black and dark brown tourmaline occur at ,town ,mountain near ,llano1 ,llano ,county4 ,the tourmaline crystals average about #a inch in length1 do not commonly exceed #b inches1 and are associated with white vein quartz4 ,the quartz completely encloses the tourmaline1 but the crystals can be broken free or the quartz can be trimmed away with the use of a diamond saw4 ,the latter procedure is recommended whenever possible1 for it is very easy to shatter the tourmaline crystals while trying to remove them from the quartz by other means4 ,many of the crystals are completely unsuitable for cutting1 being too brittle or too badly cracked and flawed4 ,however1 some small crystals have been found that are of sufficient quality and size to yield flawless stones of a few carats4 ,few of these stones have been cut since the tourmaline is so dark that it appears opaque1 and few persons find a gem of this nature attractive4 ,good black and dark brown crystals of tourmaline associated with andalusite and graphite occur in the ,packsaddle schist 7,precambrian7 near ,sunrise ,beach1 ,llano ,county 7,pl4 ,,vi1 ,b1 and fig4 #bj74 ,although generally smaller in diameter than the crystals found at ,town ,mountain1 they commonly exceed #c inches in length1 although the average size is a little over #a inch4 ,many of these crystals are suitable for cutting into opaque or nearly opaque stones of about #e or #f carats4 ,black tourmaline has also been found in ,hudspeth and ,culberson counties but not of sufficient quality to be used as a gemstone4 ,illustration3 ,fig4 #bj4 ,common crystal form of ,llano ,county tourmaline4 ,turquoise ,composition3 hydrous phosphate of aluminum and copper4 ,crystal system3 triclinic4 ,hardness3 #e to #f4 ,specific gravity3 variable1 #b4f to about #b4h4 ,luster3 dull1 sometimes waxy4 ,color3 sky blue to greenish blue4 ,streak3 white to greenish4 ,cleavage3 none in massive material1 two directions in crystals4 ,fracture3 conchoidal to subconchoidal4 ,tenacity3 brittle4 ,diaphaneity3 subtranslucent to opaque4 ,refractive index3 #a4fa to #a4fe4 ,turquoise of good sky-blue to greenish-blue color has been found a few miles southwest of ,van ,horn1 ,culberson ,county4 ,several shallow pits were dug at this locality about #aiaj2 however1 the amount of turquoise produced was small4 ,the main occurrence of the turquoise was in seams about #a millimeter thick along joints in the fine-grained rocks of this area4 ,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 pits4 ,however1 further prospecting in the area might yield some additional localities4 ,small amounts of turquoise have been reported near ,el ,paso1 ,el ,paso ,county1 and also in volcanic rocks near the ,jeff ,davis-,brewster ,county line1 north of ,alpine4 ,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 ,county4 ,,glossary ,amorphous--without definite molecular structure2 not crystalline4 ,baroque stone--an irregularly shaped1 polished stone2 usually applied to tumbled stones4 ,baroque pearl--an irregularly shaped pearl4 ,brilliancy--reflecting much light2 having brightness4 ,brilliant cut--a mode of arrangement of facets commonly used on round or oval stones4 ,the standard ,american brilliant cut has #eg or #eh facets4 ,most diamonds of #e or less carats are cut in this manner4 ,cabochon--a stone cut with a flat or convex upper surface2 sometimes faceted in part4 ,opal1 star sapphire1 and agate are stones that are frequently cut in this style 7fig4 #b74 ,cambrian--a division of geologic time1 estimated to be the time from #eej to #ddj million years ago2 the oldest time division of the ,paleozoic era4 ,carat--a unit of weight equal to of a gram or #j4b gram4 ,one ounce avoirdupois is equal to #ada4ge carats4 ,cleavage--the tendency of certain minerals to split in particular directions yielding relatively smooth plane surfaces4 ,conchiolin--an organic albuminoid substance found in pearls4 ,conchoidal--a type of fracture having curved concavities or the approximate shape of one-half of a bivalve shell4 ,glass has excellent conchoidal fracture4 ,cretaceous--a division of geologic time1 estimated to be the time from #ace to #fj million years ago2 youngest division of the ,mesozoic era4 ,crown--that portion of a faceted gem above the girdle2 the upper portion of a facet-cut gem 7fig4 #f74 ,cryptocrystalline--composed of very fine or microscopic crystals4 ,crystal--the regular polyhedral form1 bounded by plane surfaces1 that is assumed by a mineral under suitable conditions4 ,crystals have definite external symmetry and internal molecular order4 ,crystalline--possessing definite internal molecular order2 not amorphous4 ,cubic--in the general shape of a cube4 ,the isometric crystal system is often called the cubic system4 ,culet--the very bottom portion of a faceted gem2 the point or line formed by the intersection of the lowest pavilion facets 7fig4 #f74 ,dendritic--branching or tree-like in form4 ,diaphaneity--relative transparency4 ,the diaphaneity of a mineral is described as transparent1 translucent1 opaque1 etc4 ,dike--a tabular rock body1 usually igneous in origin1 which cuts across the surrounding rock strata4 ,dispersion--a measure of the ability of gemstones to separate complex or white light into its component colors2 often illustrated with a prism4 ,gemstones that are capable of separating colors of light widely are said to have high dispersion2 gemstones not so capable of separating white light into colors are said to have low dispersion4 ,dopping--the act of cementing a gemstone1 either rough or partly finished1 to a dop-stick4 ,dop-stick--the wooden stick or cylindrical piece of metal to which a gemstone is cemented to facilitate handling during cutting and polishing4 ,dop-wax--the agent or cement used to secure a gemstone to a dop-stick4 ,emerald cut--a rectangular or square faceted stone with beveled corners whose surfaces are covered with several series of rectangular facets4 ,eocene--a division of geologic time1 estimated to be the time from #ej to #dj million years ago2 one of the older divisions of the ,cenozoic era4 ,extrusive rock--igneous rock that has been extruded or forced out onto the earth's surface4 ,facet--a single plane polished surface on a faceted gem4 ,facet head--a device used in the cutting and polishing of faceted gems2 used to control the placement of facets and their relative angles 7fig4 #g74 ,facet table--the equipment used in the cutting and polishing of faceted gems and the table on which most of the equipment is mounted 7fig4 #g74 ,feldspar--a group of closely related silicate minerals including orthoclase1 microcline1 sanidine1 plagioclase1 labradorite1 and others4 ,fire--the reflections of variously colored light from a precious opal2 also the different colors of light reflected from a faceted gem owing to the dispersion of the mineral4 ,fracture--the texture of a freshly broken surface other than a cleavage surface1 described as conchoidal1 even1 splintery1 etc4 ,gem--a cut and polished gemstone4 ,gemology--the science dealing with the study of gemstones4 ,gemstone--a mineral suitable for cutting into a gem2 the term gemstones is frequently used collectively to include both cut and polished stones and rough stones4 ,geode--a rounded or spherical rock cavity2 commonly lined with crystals4 ,girdle--the portion of a faceted gem separating the crown from the pavilion2 the girdle may or may not be polished and usually contains about #b percent of the total depth of the gem 7fig4 #f74 ,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 schistosity4 ,grain 7pearl grain7--a unit of weight equal to #j4je gram or #j4be carat2 not the same as the ,troy grain4 ,granite--a granular igneous rock composed mostly of quartz1 feldspar1 and commonly mica and_/or hornblende4 ,hexagonal--having six angles and six sides2 a crystal system in which the crystal faces are referred to four intersecting axes2 three of these axes are equal1 lie in the same plane1 and intersect at angles of #fj degrees2 the fourth axis is perpendicular to the other three4 ,igneous rock--rock formed by solidification from a hot melt4 ,index of refraction--a measure of the relative ability of a gemstone to 8bend0 incident light rays2 sine of the angle of incidence of a light ray divided by the sine of the angle of refraction4 ,intrusive rock--rock that has been pushed 7usually in a molten state7 among pre-existing rock strata1 commonly along faults or fissures4 ,intrusive rocks do not reach the earth's surface but are commonly exposed at the surface by later erosion4 ,isometric--a crystal system in which the crystal faces are referred to three equal intersecting axes at right angles to each other4 ,lap--a disc-shaped piece of metal or other material which is impregnated with diamond dust1 or some other cutting or polishing agent1 that is revolved while the gemstone is worked against it4 ,lap plate--a metal plate to which a cutting or polishing lap is attached1 usually by means of a threaded bolt and wing nut4 ,the lap plate is attached to the shaft which is turned by the motor under the facet table4 ,lapidary--one who practices the lapidary arts2 a gem cutter4 ,limestone--a sedimentary rock composed mostly of calcium carbonate4 ,luster--the appearance of the freshly broken or unweathered surface of a mineral in reflected light 7p4 #e74 ,main facet--as applied to the standard ,american brilliant cut1 one of the first eight facets cut on either the crown or pavilion of a gem 7fig4 #f74 ,matrix--the material in which a specific mineral is embedded2 also the rock to which one end of a crystal is attached4 ,metamorphic rock--rock that has been changed from its original state by heat1 pressure1 chemical action1 or some combination of these factors4 ,millimeter--_/ centimeter2 approximately _/ inch4 ,mineralogy--the science concerned with the study of minerals1 including their occurrence1 composition1 forms1 properties1 and structure4 ,monoclinic--a crystal system in which the crystal faces are described in relation to three intersecting unequal axes1 two of which are at right angles and the third inclined4 ,oligocene--a division of geologic time1 estimated to be the time from #dj to #bh million years ago2 part of the ,cenozoic era4 ,opaque--does not transmit light4 ,orbicular--containing orbs or spherical or eye-like markings or structures4 ,orthorhombic--a crystal system in which crystal faces are referred to three unequal intersecting axes at right angles4 ,pavilion--the portion of a faceted gem below the girdle 7fig4 #f74 ,pegmatite--a body of coarse-grained intrusive igneous rock1 commonly lens or dike shaped4 ,perthitic--a plaid-patterned structure resulting from intermixture of soda- and potash-rich feldspars4 ,phantom crystal--a crystal outline seen within another crystal1 mostly due to entrapping of inclusions during the crystal's growth4 ,pleochroism--the property of transmitting different colors of light in different crystallographic directions4 ,point--a unit of weight equal to _/ 7#j4ja7 carat4 ,porous--containing pores or void spaces4 ,precambrian--a division of geologic time1 estimated to be all of geologic time prior to #eej million years ago2 the time before the ,paleozoic era4 ,preform--a gemstone that has been ground to a rough outline of the finished shape of a gem4 ,rhyolite--a fine-grained extrusive or shallow intrusive igneous rock of approximately the same composition as granite4 ,rough--uncut1 not worked by a lapidary1 not cut and polished4 ,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 minerals4 ,silicified--replaced by or containing a large amount of quartz or silica4 ,skill facet--a term often used for the pavilion girdle facets of the standard ,american brilliant cut 7fig4 #f74 ,specific gravity--the weight in air divided by the loss of weight in water at a given temperature1 or the weight of an object in air divided by the weight of an equal volume of water2 also called relative density2 the most commonly used standard temperature for this measurement is #d ,c4 or #ci4b ,f4 ,star facet--one of the eight facets surrounding the table facet of a standard ,american brilliant cut 7fig4 #f74 ,step cut--a mode of faceting in which the surface of the gem is covered by a series of square or rectangular facets2 stones thusly cut are usually square1 rectangular1 or irregular with straight sides in outline4 ,streak--the color of a mineral when finely powdered2 usually determined by rubbing the mineral against a piece of unglazed porcelain4 ,symmetry--the number1 location1 and balanced arrangement of crystal faces in reference to the crystallographic axes or other crystallographic planes or directions4 ,synthetic gem--a gemstone manufactured by man that has approximately the same chemical composition and properties as a natural gemstone4 ,table facet--the large horizontal facet found on the crown of many gems1 often called simply the table 7fig4 #f74 ,tenacity--the resistance of minerals to breakage1 described by such terms as malleable1 ductile1 sectile1 and brittle 7p4 #f74 ,termination--the end of a crystal that is completely enclosed by crystal faces1 the crystal end that is not attached to the matrix4 ,tertiary--a division of geologic time1 estimated to be the time from #fj to #a million years ago2 the ,tertiary includes the ,paleocene1 ,eocene1 ,oligocene1 ,miocene1 and ,pliocene epochs 7from oldest to youngest74 ,tetragonal--having four angles2 a crystal system in which the crystal faces are referred to three axes at right angles to each other1 two of which are equal and the third longer or shorter4 ,translucent--allowing the passage of light but diffusing it sufficiently so that objects on the other side cannot be clearly distinguished4 ,transparent--clear1 allowing free passage of light so that objects on the other side can be readily distinguished2 opposite of opaque4 ,triclinic--a crystal system in which the crystal faces are referred to three unequal axes1 none of which are at right angles4 ,tumbling--a process of polishing irregularly shaped gemstones 7p4 #ag74 ,vein--a tabular1 irregular1 or twisting mineral deposit that is thin in relation to its length and breadth1 usually the result of solution or hydrothermal activity4 ,vitreous--having luster1 general appearance1 or physical properties similar to glass4 ,vug--an unfilled rock cavity1 commonly lined with crystals2 may later become filled by minerals owing to solution or hydrothermal activity4 ,,selected ,,references ,anderson1 ,b4 ,w4 7#aidh7 ,gem testing3 ,emerson1 ,new ,york4 ,baker1 ,c4 ,l4 7#aice7 ,metallic and non-metallic minerals and ores 7precious stones71 in ,the geology of ,texas1 ,vol4 ,,ii1 ,structural and economic geology3 ,univ4 ,texas ,bull4 #cdja1 ,jan4 #a1 #aicd1 pp4 #efh-efi4 ,barnes1 ,v4 ,e4 7#aidj7 ,north ,american tektites3 ,univ4 ,texas ,pub4 #cide1 ,dec4 #a1 #aici1 pp4 #dgg-ehb4 ,dake1 ,h4 ,c41 ,fleener1 ,f4 ,l41 and ,wilson1 ,b4 ,h4 7#aich7 ,quartz family minerals3 ,whittlesey ,house1 ,mc,graw-,hill ,book ,company1 ,inc41 ,new ,york4 ,ford1 ,w4 ,e4 7#aicb7 ,a textbook of mineralogy 7#dth ed473 ,john ,wiley and ,sons1 ,inc41 ,new ,york4 ,kraus1 ,e4 ,h41 and ,slawson1 ,c4 ,b4 7#aidg7 ,gems and gem materials 7#eth ed473 ,mc,graw-,hill ,book ,company1 ,inc41 ,new ,york4 ,kunz1 ,g4 ,f4 7#ahib7 ,gems and precious stones of ,north ,america 7#b;d ed473 ,scientific ,publishing ,company1 ,new ,york4 ,pough1 ,f4 ,h4 7#aiec7 ,a field guide to rocks and minerals3 ,houghton ,mifflin ,company1 ,boston4 ,simpson1 ,b4 ,w4 7#aieh7 ,gem trails of ,texas3 ,granbury1 ,texas4 ,sinkankas1 ,john 7#aiee7 ,gem cutting3 ,d4 ,van ,nostrand ,company1 ,inc41 ,princeton1 ,new ,jersey4 ---- 7#aiei7 ,gemstones of ,north ,america3 ,d4 ,van ,nostrand ,company1 ,inc41 ,princeton1 ,new ,jersey4 ,smith1 ,g4 ,f4 ,h4 7#aieh7 ,gemstones 7#acth ed471 revised by ,f4 ,c4 ,phillips3 ,methuen and ,company1 ,ltd41 ,london4 ,sperisen1 ,f4 ,j4 7#aiej7 ,the art of the lapidary3 ,the ,bruce ,publishing ,company1 ,milwaukee1 ,wisconsin4 ,sterrett1 ,d4 ,b4 7#aiac7 ,gems and precious stones1 in ,mineral resources of the ,united ,states1 ,calendar ,year #aiab1 ,part ,,ii1 ,non-metals3 ,u4 ,s4 ,geol4 ,survey1 pp4 #ajbc-ajfj4 ,plate ,i ,illustration3 ,a ,gem-quality celestite crystals from ,travis ,county1 ,texas4 ,twice natural size4 ,lower portion of the crystals is colorless2 the tips are dark blue4 ,illustration3 ,b ,opalized wood from the ,texas ,gulf ,coastal ,plain4 ,specimen at left is rich brown and tan2 specimen at right is fossil palm wood and is black1 reddish brown1 and white4 ,one-third natural size4 ,plate ,,ii ,illustration3 ,a ,gem-quality garnet crystals and faceted gem from ,gillespie ,county1 ,texas4 ,natural size4 ,illustration3 ,b ,labradorite from ,brewster ,county1 ,texas4 ,both stones are pale yellow4 ,one and a half times natural size4 ,plate ,,iii ,illustration3 ,a ,pink microcline crystal from ,burnet ,county1 ,texas4 ,illustration3 ,b ,smoky quartz from ,burnet ,county1 ,texas4 ,natural size4 ,colorless crystal at center back is included for color comparison4 ,plate ,,iv ,illustration3 ,polished agate from gravels of the ,rio ,grande near ,zapata1 ,zapata ,county1 ,texas4 ,bands are blue and gray2 other inclusions are brown1 yellow1 and reddish4 ,one and a half times natural size4 ,plate ,v ,illustration3 ,a ,texas tektites 7bediasites7 showing variety of surface features4 ,natural size4 ,illustration3 ,b ,topaz crystal from a pegmatite dike near ,streeter1 ,mason ,county1 ,texas4 ,natural size4 ,measurements3 #a by #a by #c inches2 weight3 #aid grams 7#igj carats72 pale blue2 mostly gem quality4 ,plate ,,vi ,illustration3 ,a ,topaz from stream gravels near ,streeter1 ,mason ,county1 ,texas4 ,natural size4 ,left to right3 colorless worn pebble2 emerald-cut pale-blue topaz1 weight #aj carats2 pale-blue worn pebble1 weight #bje carats2 step out sky-blue topaz1 weight #ac carats2 pale-blue worn pebble4 ,illustration3 ,b ,tourmaline crystals in schist from ,llano ,county1 ,texas4 ,index ,a actinolite3 #bf agate3 #bj1 #bh1 #ch agatized wood3 #bg allanite3 #ba almandite3 #bb amazonite3 #bc amazon stone3 #bc amber3 #ah amethyst3 #be ,amethyst ,hill3 #be amorphous gemstones3 #i andalusite3 #cj ,arkansas3 #ai ,armstrong ,county3 #ba augite3 #ah1 #bh ,b ,baringer ,hill1 ,llano ,county3 #ba1 #bf baroque pearls and_/or stones3 #ag1 #be bediasite 7tektite73 #bh-bi1 #ci beryl3 #ah ,big ,bend ,national ,park3 #bg biotite3 #bc ,blanco ,county3 #ah1 #bb ,brazos ,county3 #bi ,brazos ,river3 #be ,brewster ,county3 #ah1 #bc1 #bd1 #be1 #bf1 #bg1 #bh1 #ca1 #cf brilliancy3 #e brilliant cut1 standard ,american3 #ac1 #ae1 #af ,brown ,county3 #ai ,burleson ,county3 #bi ,burnet ,county3 #bj1 #bb1 #bc1 #be1 #bf1 #cj1 #cg ,c cabochon gems3 #aj-ab ,caddo ,lake3 #be carbuncle3 #bb carnelian3 #bg cassiterite3 #bc1 #bi celestite3 #ai1 #ce chalcedony3 #bg geodes3 #bf chuck3 #ae1 #ag citrine3 #be-bf cleavage3 #f1 #ac coal3 #bb ,coke ,county3 #ai color3 #e ,colorado ,river3 #be ,concho ,river3 #be crown girdle facets3 #af1 #ag crown of gemstone3 #ae1 #af crystals3 #g-i crystal systems3 #g crytolite3 #ba ,culberson ,county3 #bb1 #bc1 #be1 #bf1 #ca culet3 #ac cutting and polishing3 #aj-ag cutting lap3 #ac ,d ,de,witt ,county3 #bi diamond3 #ai saw3 #aj1 #aa diaphaneity3 #e dispersion3 #f dopping3 #ab1 #ac dop-stick3 #ab1 #ae1 #ag dop-wax3 #ab1 #ae1 #ag dravite3 #cj durability3 #f ,duval ,county3 #ba1 #bd ,e ,el ,paso ,county3 #bb1 #cj1 #ca emerald cut3 #ae epidote3 #ai-bj ,f facet1 kinds of3 #ac main3 #af skill3 #af table3 #ac1 #ad faceted gems and_/or stones3 #aj1 #ac-ag ,fayette ,county3 #bj1 #bi fergusonite3 #ba fire3 #e ,fisher ,county3 #ai fluorite3 #bj1 #ba ,foard ,county3 #ai fossil wood3 #bj-ba1 #bb fracture3 #f ,franklin ,mountains3 #ah ,g gadolinite3 #ba-bb garnet3 #bj1 #bb1 #cf gemstones1 by kinds3 #ah-ca geodes1 celestite3 #ai ,georgia3 #bi ,gillespie ,county3 #ah1 #bb1 #bc1 #be1 #bf1 #cj1 #cf girdle facets3 #af gneiss3 #bb ,gonzales ,county3 #bj1 #bi grain3 #be gram3 #g graphite3 #cj ,grimes ,county3 #bi grinding3 #ab ,guadalupe ,river3 #be ,gulf ,coast3 #be ,gulf ,coastal ,plain3 #ah1 #bj1 #bb1 #ce ,h hardness3 #f ,hudspeth ,county3 #ah1 #bj1 #bb1 #bd1 #be1 #bf1 #bg1 #bh1 #ca ,i index of refraction3 #e ,j jasper3 #bg-bh ,jeff ,davis ,county3 #bf1 #bg1 #bh1 #ca jet3 #bb ,k ,kinney ,county3 #bh ,l labradorite3 #bc1 #cf ,lake ,buchanan3 #ba ,lampasas ,county3 #ai lap plate3 #ac ,lavaca ,county3 #bi ,lee ,county3 #bj1 #bi lignite3 #bb ,live ,oak ,county3 #ba ,llano ,county3 #ah1 #ai1 #bj1 #ba1 #bb1 #bc1 #be1 #bf1 #cj1 #ca1 #dj ,llano ,river3 #be luster3 #e ,m ,madeira topaz3 #bi ,mason ,county3 #bj1 #bb1 #bc1 #bf1 #bi1 #cj1 #ci1 #dj ,massachusetts3 #bi ,maverick ,county3 #ah microcline3 #bj1 #ba1 #bc-bd1 #bi1 #cg ,mohs scale of hardness3 #f moonstone3 #bh ,mount ,bonnell3 #ai muscovite3 #bc ,n natural glass3 #ah1 #bd1 #bh ,needle ,peak1 ,presidio ,county3 #bg nivenite3 #ba ,nolan ,county3 #ai ,nueces ,river3 #be ,o obsidian3 #bd1 #bi ,oklahoma3 #bi opal3 #bj1 #bd opalized wood3 #ce orbicular jasper3 #bh ounce3 #g ,p ,packsaddle ,mountain3 #bc ,packsaddle schist3 #cj palm wood3 #ba1 #ce ,palo ,duro ,canyon3 #ba pavilion3 #ac1 #af facets3 #af girdle facets3 #af1 #ag pearl3 #bd-be pegmatites and_/or pegmatite dikes3 #ah1 #bj1 #ba1 #bb1 #bc1 #bf1 #bi1 #ci petrified wood3 #bf phantom crystals3 #bf pistacite3 #bj pleochroism3 #e point3 #g polishing3 #ag lap3 #ac1 #af preformed stone3 #af preforming3 #ae ,presidio ,county3 #bj1 #bb1 #bd1 #be1 #bf1 #bg1 #bh properties of gemstones3 #e-g ,q quartz3 #bj1 #ba1 #bc1 #be-bh1 #bi1 #cj smoky3 #ch ,r radioactive elements3 #bb radioactivity of gadolinite3 #ba rarity3 #f ,reeves ,county3 #bf1 #bg ,rio ,grande3 #be gravels of3 #ba1 #bg1 #ch ,valley3 #bg rock crystal3 #bf rose quartz3 #bf ,s ,sabine ,river3 #be sanding3 #ab sanidine3 #bh sawing3 #aj scheelite3 #bj schorl3 #cj size3 #g 8skill0 facets3 #af 8slab0 of gem materials3 #aa ,smithsonian ,institution3 #ba smoky quartz3 #bc1 #bf1 #cg smoky topaz3 #bi ,spanish topaz3 #bi specific gravity3 #g spinel3 #ah1 #bh star facets3 #ag step cut3 #ae streak3 #f synthetic gems3 #g ,t table facet3 #ac1 #ae tektite 7bediasite73 #bh-bi1 #ci tenacity3 #f thorogummite3 #ba topaz3 #bc1 #bf1 #bi-cj1 #ci1 #dj quartz3 #bi tourmaline3 #bf1 #bi1 #cj-ca1 #dj ,town ,mountain1 ,llano ,county3 #bf1 #cj transparency3 #f ,travis ,county3 #ai1 #ce ,trinity ,river3 #be tumbled gems3 #ag turquoise3 #ca ,u ,u4 ,s4 ,national ,museum3 #cj ,v value of gemstones3 #f1 #g ,val ,verde ,county3 #bd valverdites3 #bd ,van ,horn1 ,hudspeth ,county3 #bg ,w ,walker ,county3 #bi ,washington ,county3 #bj ,webb ,county3 #ba weight1 units of3 #g1 #be ,z ,zapata ,county3 #ch ,transcriber's ,notes --,silently corrected a few typos4 --,renumbered figures #f and #g 7and references to them7 to correspond to their order in the printed book4 --,retained publication information from the printed edition3 this e,book is public-domain in the country of publication4 --,in the text versions only1 text in italics is delimited by underscores4