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| committer | nfenwick <nfenwick@pglaf.org> | 2025-02-04 03:07:08 -0800 |
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} - -.fnblock { margin-top:2em; margin-bottom:2em; } -.fndef, p.fn { text-align:justify; margin-top:1.5em; margin-left:1.5em; text-indent:-1.5em; } -.fndef p.fncont, .fndef dl { margin-left:0em; text-indent:0em; } -.fnblock div.fncont { margin-left:1.5em; text-indent:0em; margin-top:1em; text-align:justify; } -.fnblock dl { margin-top:0; margin-left:4em; text-indent:-2em; } -.fnblock dt { text-align:justify; } -dl.catalog dd { font-style:italic; } -dl.catalog dt { margin-top:1em; } -.author { text-align:right; margin-top:0em; margin-bottom:0em; display:block; } - -dl.biblio dt { margin-top:.6em; margin-left:2em; text-indent:-2em; text-align:justify; clear:both; } -dl.biblio dt div { display:block; float:left; margin-left:-6em; width:6em; clear:both; } -dl.biblio dt.center { margin-left:0em; text-align:center; text-indent:0; } -dl.biblio dd { margin-top:.3em; margin-left:3em; text-align:justify; font-size:90%; } -p.biblio { margin-left:2em; text-indent:-2em; } -.clear { clear:both; } -p.book { margin-left:2em; text-indent:-2em; } -p.review { margin-left:2em; text-indent:-2em; font-size:80%; } -p.pcap { text-indent:0; text-align:justify; margin-top:0; max-width:35em; margin-left:auto; margin-right:auto; font-size:85%; } -dl.pcap { font-size:85%; } -p.pcapc { margin-left:4.7em; text-indent:0em; text-align:justify; } -span.attr { font-size:80%; font-family:sans-serif; } -span.pn { display:inline-block; width:4.7em; text-align:left; margin-left:0; text-indent:0; } -</style> -</head> -<body> - - -<pre> - -Project Gutenberg's Gems in the Smithsonian Institution, by Paul E. Desautels - -This eBook is for the use of anyone anywhere in the United States and most -other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms of -the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - -Title: Gems in the Smithsonian Institution - -Author: Paul E. Desautels - -Release Date: August 8, 2020 [EBook #62879] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK GEMS IN THE SMITHSONIAN INSTITUTION *** - - - - -Produced by Stephen Hutcheson and the Online Distributed -Proofreading Team at https://www.pgdp.net - - - - - - -</pre> - -<div id="cover" class="img"> -<img id="coverpage" src="images/cover.jpg" alt="Gems in the Smithsonian Institution" width="500" height="771" /> -</div> -<div class="img" id="fig1"> -<img src="images/p03.jpg" alt="" width="600" height="800" /> -<p class="pcap">Faceted, egg-shaped, 7000-carat rock crystal from Brazil. The gold -stand is inset mostly with Montana sapphires. The gem was cut and -the stand was designed and constructed by Capt. John Sinkankas of -California. (7¼ inches high in all.)</p> -</div> -<div class="box"> -<h1><span class="xxlarge"><i>Gems</i></span> -<br /><span class="smaller"><i>in the</i> -<br />SMITHSONIAN -<br />INSTITUTION</span></h1> -<p class="tbcenter"><span class="large">by PAUL E. DESAUTELS</span></p> -<p class="center"><i>Associate Curator</i> -<br />Division of Mineralogy</p> -<p class="center"><span class="smaller">WASHINGTON, D. C.</span> -<br />1965</p> -</div> -<div class="img"> -<img src="images/p04.jpg" alt="FOR THE INCREASE AND DIFFVSION OF KNOWLEDGE AMONG MEN • SMITHSONIAN INSTITVTION • WASHINGTON 1846" width="356" height="349" /> -</div> -<p class="center small">SMITHSONIAN -<br />INSTITUTION -<br /><span class="smaller">PUBLICATION</span> -<br />No. 4608</p> -<p class="center small"><span class="smaller">LIBRARY OF CONGRESS</span> -<br /><span class="sc">Card No.</span> 65-60068</p> -<h2 id="toc" class="center">CONTENTS</h2> -<dl class="toc"> -<dt><a href="#c1">The National Gem Collection</a> 1</dt> -<dt><a href="#c2">The Study of Gems</a> 3</dt> -<dt><a href="#c3">The Shaping of Gemstones</a> 10</dt> -<dt><a href="#c4">Gem Substitutes</a> 20</dt> -<dt><a href="#c5">Gem Lore</a> 24</dt> -<dt><a href="#c6">The Principal Gem Species</a> 27</dt> -<dt><a href="#c7">Some Notable Gems in the Collection</a> 70</dt> -</dl> -<div class="img" id="fig2"> -<img src="images/p05.jpg" alt="" width="400" height="476" /> -<p class="pcap">Prof. F. W. Clarke, former honorary curator of -the Division of Mineralogy who assembled the -Smithsonian Institution’s first gem collection in -1884.</p> -</div> -<div class="img" id="fig3"> -<img src="images/p05a.jpg" alt="" width="400" height="494" /> -<p class="pcap">Dr. Isaac Lea, Philadelphia gem collector whose -collection was the nucleus around which the -Smithsonian Institution’s gem collection has been -built through the years.</p> -</div> -<div class="img" id="fig4"> -<img src="images/p05b.jpg" alt="" width="400" height="480" /> -<p class="pcap">Dr. Leander T. Chamberlain, son-in-law of Dr. -Isaac Lea, who became honorary curator of the -Smithsonian Institution’s gem collection in 1897. -Income from his bequest is used to purchase -gems for the Isaac Lea gem collection.</p> -</div> -<div class="pb" id="Page_1">1</div> -<h2 id="c1"><span class="small">1</span> -<br />THE NATIONAL GEM COLLECTION</h2> -<p>Man has been using certain mineral species for personal -adornment since prehistoric times. However, of the -almost 2000 different mineral species, relatively few, -perhaps only 100, have been used traditionally as gems. To be -used as a gem, a mineral species must have durability as well as -beauty. Lack of durability eliminates most minerals as gems, -although some relatively fragile gem materials such as opal are -prized because of their exceptional beauty. Actually, some gem -materials are not minerals at all. Pearl, amber, jet, and coral -are formed by living organisms.</p> -<p>In the National Gem Collection, the Smithsonian Institution -has assembled a large representation of all known gem materials. -The display portion of the collection consists of more -than 1000 items selected to illustrate the various kinds of gems -and to show how their beauty is enhanced by cutting and -polishing. All of these gems are gifts of public-spirited donors -who, by giving the gems directly or by establishing endowments -for their purchase, have contributed to the enjoyment of -the many thousands of persons who visit the Smithsonian -Institution each week.</p> -<p>The National Gem Collection had its beginning in 1884 -when Prof. F. W. Clarke, then honorary curator of the Division -of Mineralogy, prepared an exhibit of American precious -stones as a part of the Smithsonian Institution’s display at the -<span class="pb" id="Page_2">2</span> -New Orleans Exposition. The same collection was displayed -at the Cincinnati Exposition the following year. Between 1886 -and 1890 the growth of the collection was slow, but in 1891 -most of the precious stones collected by Dr. Joseph Leidy of -Philadelphia were obtained, and these, combined with those -already on hand, were exhibited at the World’s Columbian -Exposition at Chicago in 1893.</p> -<p>Great stimulus was given the collection in 1894 when Mrs. -Frances Lea Chamberlain bequeathed the precious stones -assembled by her father, Dr. Isaac Lea. Her husband, Dr. -Leander T. Chamberlain, who in 1897 became honorary -curator of the collection, contributed a large number of specimens -and, upon his death, left an endowment fund. The income -from that fund has been used to steadily increase the collection -over the years. Extremely rare and costly gems suitable for -exhibition are beyond the income derived from the Chamberlain -endowment, but this gap has been filled by many important -donations, the most notable being the gift of the Hope Diamond -by Harry Winston, Inc., New York City. Thus, from modest -beginnings in 1884, there has been accumulated the magnificent -collection of gems belonging to the people of the United States. -The collection is displayed in the Smithsonian Institution’s -great Museum of Natural History.</p> -<div class="img" id="fig5"> -<img src="images/p06.jpg" alt="" width="800" height="316" /> -<p class="pcap">Left to right: 42-carat brazilianite, 8.4-carat euclase, 7.6-carat benitoite, -12-carat willemite, 20-carat amblygonite, and 16-carat orthoclase. -(About two-thirds actual size.)</p> -</div> -<div class="pb" id="Page_3">3</div> -<h2 id="c2"><span class="small">2</span> -<br />THE STUDY OF GEMS</h2> -<p>To the average person it might seem that a jeweler’s showcase -of gems presents innumerable kinds of precious -stones, when actually only a few species of minerals are -there. Perhaps only diamond, ruby, emerald, aquamarine, -sapphire, opal, tourmaline, and amethyst would comprise the -entire stock. Yet, since the mineral kingdom consists of about -2000 distinct species, it would seem that a few more kinds of -gemstones would be available. Certainly, many more minerals -than are seen displayed by the jeweler have been used as gems -over the centuries. The study of all these species of gem minerals -constitutes modern gemology—a specialized branch of -the science of mineralogy.</p> -<p>With the few exceptions already noted, all gems are minerals -found in the earth’s crust. A mineral is a natural substance -having a definite chemical composition and definite physical -characteristics by which it can be recognized. However, for a -mineral to qualify as a gem it must have at least some of the -accepted requirements—brilliance, beauty, durability, rarity, -and portability. Of course, if a gemstone happens to be -“fashionable” it will have additional importance. Rarely does -a single gem possess all of these qualities. A fine-quality -diamond, having a high degree of brilliance and fire, together -with extreme hardness and great rarity, comes closest to this -ideal, and in the world of fashion the diamond is unchallenged -among gems. The opal, by contrast, is relatively fragile, and it -<span class="pb" id="Page_4">4</span> -depends mainly on its rarity and its beautiful play of colors -to be considered gem material.</p> -<p>When a gem material, as found in nature, has at least a -minimum number of the necessary qualities, it is then the task -of the lapidary, or gem cutter, to cut it and polish it in such a -way as to take greatest advantage of all its possibilities for -beauty and adornment.</p> -<h3>PHYSICAL CHARACTERISTICS OF GEMSTONES</h3> -<p>When a gemologist or a gem cutter examines an unworked -mineral fragment (called <i>rough</i>) he looks for certain -distinguishing characteristics that will aid him in identifying -the mineral and in determining the procedures he should -use in cutting it.</p> -<table class="center"> -<tr class="th"><th colspan="2">Scale of Hardness</th></tr> -<tr><td class="c">Soft </td><td class="l">1. Talc</td></tr> -<tr><td class="c">^ </td><td class="l">2. Gypsum</td></tr> -<tr><td class="c"> </td><td class="l">3. Calcite</td></tr> -<tr><td class="c"> </td><td class="l">4. Fluorite</td></tr> -<tr><td class="c"> </td><td class="l">5. Apatite</td></tr> -<tr><td class="c"> </td><td class="l">6. Feldspar</td></tr> -<tr><td class="c"> </td><td class="l">7. Quartz</td></tr> -<tr><td class="c"> </td><td class="l">8. Topaz</td></tr> -<tr><td class="c"><span class="ssn">v</span> </td><td class="l">9. Corundum</td></tr> -<tr><td class="c">Hard </td><td class="l">10. Diamond</td></tr> -</table> -<p>It is difficult to list these characteristics in the order of -importance, but <i>hardness</i> would rank high. Hardness of a gem is -best defined as its resistance to abrasion or scratching. Most -commonly used for comparison is the Mohs scale, which consists -of selected common minerals -arranged in the order of increasing -hardness. On this scale, -topaz is rated as 8 in hardness, -ruby as 9, and diamond, the -hardest known substance, as 10. -Any gem with a hardness less -than that of quartz, number 7 -in the scale, is unlikely to be -sufficiently scratch-resistant for -use as a gem. A less precise -scale, using common objects for -comparison, might include the -fingernail with a hardness up to -<span class="pb" id="Page_5">5</span> -2½, a copper coin up to 3, a knife blade to 5½, a piece of -window glass at about 5½, and a steel file between 6 and 7, -depending on the type of steel. By this scale, any stone that -remains unmarred after being scraped by a piece of window -glass will have a hardness greater than 5½. The more important -gemstones—which include diamond, ruby, sapphire, and -emerald—all have a hardness much greater than 5½.</p> -<p>The size of a gemstone usually is indicated by its <i>weight</i> in -carats. The expression “a 10-carat stone” has meaning—if -somewhat inexact—even to the nonexpert. Specifically, a -carat is one-fifth of a gram, which is a unit of weight in the -metric system small enough so that approximately 28 grams -make an ounce. A 140-carat gemstone, then, weighs about an -ounce.</p> -<p>Another distinguishing characteristic of a gemstone is its -specific gravity, which is an expression of the relationship between -the stone’s own weight and the weight of an equal volume of -water. We are aware of a difference in weight when we compare -lead and wood, yet it would not always be correct to say -that lead weighs more than wood, for a large piece of wood -can weigh more than a small piece of lead. Only by comparing -equal volumes of these materials can the extent of the weight -difference be clear and unmistakable. Diamond is 3½ times -heavier than the same volume of water, so its specific gravity -is 3.5. Since each species of gem has its own specific gravity, -which can be determined without harming the stone, this -standard of comparison is a valuable aid in identifying gems. -Several techniques have been devised for determining specific -gravity, and most of them make use of some kind of weighing -device or balance.</p> -<p>Among the most striking and useful of the distinguishing -characteristics of gemstones are those that involve the effects -on light.</p> -<p>An important effect of a gem on light is the production of -color, upon which many gems depend for their beauty. Some -gem materials, such as lapis lazuli, have little to offer except -color. Many gemstones vary widely in color, owing to the -presence of varying but extremely small amounts of impurities. -<span class="pb" id="Page_6">6</span> -Thus, the gemstone beryl may occur as blue-green (aquamarine), -as pink (morganite), as rich green (emerald), as -yellow (golden beryl), or even colorless (goshenite).</p> -<div class="img" id="fig6"> -<img src="images/p07.jpg" alt="" width="800" height="317" /> -<p class="pcap">Sketch of a simple balance used to determine specific gravity of a -gemstone. The operator places the gemstone in the upper pan (A), -moves the weight (B) along the beam (C) until it balances perfectly, -and notes the number at the weight’s position. He then transfers -the gemstone to the lower pan (D), which is completely immersed -in water, and moves the weight along the beam to restore balance. -He notes the scale number at the new position and determines the -specific gravity simply by dividing the first number by the difference -between the two numbers. If the gemstone is large, the operator can -use heavier sliding weights. (E).</p> -</div> -<p>Gemstones such as beryl and sapphire that depend on impurities -for their color are said to be <i>allochromatic</i>; others, such -as peridot and garnet, which are highly colored even when -pure, are said to be <i>idiochromatic</i>. The color of a gem is further -described according to its <i>hue</i>, <i>tint</i>, and <i>intensity</i>. Hue refers to -the kind of color, such as red, yellow, green, etc.; tint refers to -the lightness or darkness of the hue; and intensity refers to -vividness or dullness. Throughout history, the most popular -colored stones have been those with hues of red, green, or blue -of dark tint and high intensity.</p> -<div class="img" id="fig7"> -<img src="images/p07a.jpg" alt="" width="800" height="233" /> -<p class="pcap">A 43-carat albite from Burma (at left), 76-carat tourmaline from -Brazil, and 30-carat wernerite from Burma exhibit a strong cat’s-eye -effect because of reflection from inclusions in parallel arrangement -within the stones. (Actual size.)</p> -</div> -<div class="pb" id="Page_7">7</div> -<div class="img" id="fig8"> -<img src="images/p07b.jpg" alt="" width="700" height="555" /> -<p class="pcap">Asterism (star effect) is caused by -parallel inclusions arranged in -several directions related to the -crystal structure of the gemstone. -Two rays in the 175-carat, 6-rayed -star garnet from Idaho (at left in -photo) are weaker than the other -four because of fewer inclusions in -that direction. The 23-carat star -orthoclase from Ceylon shows -brightly all of its four possible rays. -(Actual size.)</p> -</div> -<p>The effect of a gem on light may be more than the production -of color. Several of the so-called phenomenal stones are prized -for other effects. Holes, bubbles, and foreign particles, when -properly aligned in parallel groupings, can produce interesting -light effects. The play of colors of opal and labradorite, the -<i>chatoyancy</i> or silky sheen of tiger’s-eye and cat’s-eye, the -<i>opalescence</i> or pearly reflections of opal and moonstone, and the -<i>asterism</i> or star effect of rubies and sapphires are caused by the -reaction of light to minute <i>inclusions</i> or imperfections in the -gemstone.</p> -<p>When light passes into or through a gemstone with little or -no interruption, the stone is said to be transparent, as opposed -to a stone through which light passes with greater difficulty, -and which is said to be either translucent or opaque, depending -on the degree of light interruption.</p> -<div class="img" id="fig9"> -<img src="images/p07g.jpg" alt="" width="500" height="436" /> -<p class="pcap">Rays of light passing into a gemstone -are refracted (bent) in varying -amounts depending on the gem -species and also on the angle at -which the light strikes the stone. -The light rays are reflected back -toward the top of the stone by -internal faces (facets), and they -are refracted again as they leave.</p> -</div> -<div class="pb" id="Page_8">8</div> -<div class="img" id="fig10"> -<img src="images/p08.jpg" alt="" width="700" height="363" /> -<p class="pcap">How a gem refractometer, a simple device to operate, is used to measure -quickly the refractive index of a cut gemstone. A light beam -passing through the opening (A) is reflected from the table of a -gemstone (G) through a lens system (L) and, by prism (P), into the -eye of the observer (E). The maximum angle of reflection (N), -which depends on the refractive index of the gemstone, controls the -angle at which the beam comes through the eyepiece (EP). The -refractive index is read directly from a scale in the eyepiece.</p> -</div> -<p>The action of a gemstone upon the light which strikes its -surface and is either reflected or passed through it sometimes -results in highly desirable effects that enhance its beauty and aid -in its identification. Light passing into a stone is bent from its -path, and the amount of bending (<i>refraction</i>) depends upon the -species of the gemstone. When the degree of bending can be -measured, the gem species can be identified, since very few -species of gemstones bend light to exactly the same degree. An -instrument called a gem refractometer is used to determine the -degree to which cut stones refract, or bend, light. The measurement -obtained is the <i>refractive index</i> of the gemstone.</p> -<p>Many gemstones can split a beam of light and bend one part -more than the other, thus producing <i>double refraction</i>, or two -different measurements of refractive index.</p> -<div class="img" id="fig11"> -<img src="images/p08a.jpg" alt="" width="500" height="484" /> -<p class="pcap">When a ray of ordinary white light enters -some gemstones it is dispersed (split up) -into rays of the separate colors of which it -is composed. These rays are reflected inside -the gem and are further separated by additional -refraction as they leave the gemstone. -This dispersion accounts for the colored -flashes of light, or fire, for which diamond -is highly prized.</p> -</div> -<div class="pb" id="Page_9">9</div> -<p>Gems have the ability to separate “white light” (the mixture -of all colors) into its various colors, producing flashes of -red, yellow, green, and other colors. Separation occurs because -the various colors, or wavelengths composing white light -passing through the gem, are each bent or refracted a different -amount. Red is bent least, followed in order by orange, -yellow, green, blue, and violet, which is bent most. This -characteristic of being able to produce flashes of color, as seen -prominently in diamond, is known as <i>dispersion</i> or <i>fire</i>. Quartz -and glass have low dispersion, and hence they make poor -diamond substitutes. Some of the newer synthetic gemstones, -such as titania, have extremely high dispersion, with resulting -fire. Zircon, a natural gemstone of suitable hardness, exhibits -high dispersion and is a commonly used substitute for -diamond.</p> -<h3>CHEMICAL CHARACTERISTICS OF GEMSTONES</h3> -<p>Since gems are embraced in the mineral kingdom, and minerals -are naturally occurring chemical substances, it follows -that all the accepted terms of chemical description can be -applied to them. When a chemist learns that ruby is an impure -aluminum oxide, he understands a great deal about the nature, -origin, and behavior of ruby. He can assign to it the chemical -formula Al₂O₃, symbolizing its basic composition as two atoms -of aluminum united with three of oxygen. Similarly, other popular -gemstones can be described chemically as follows:</p> -<table class="center"> -<tr><td class="l">Diamond </td><td class="l">Carbon </td><td class="l">C</td></tr> -<tr><td class="l">Sapphire </td><td class="l">Aluminum oxide </td><td class="l">Al₂O₃</td></tr> -<tr><td class="l">Quartz </td><td class="l">Silicon dioxide </td><td class="l">SiO₂</td></tr> -<tr><td class="l">Emerald </td><td class="l">Beryllium aluminum silicate </td><td class="l">Be₃Al₂(SiO₃)₆</td></tr> -<tr><td class="l">Spinel </td><td class="l">Magnesium aluminate </td><td class="l">Mg(AlO₂)₂</td></tr> -</table> -<div class="pb" id="Page_10">10</div> -<p>Significantly, ruby and sapphire are chemically identical, both -being of the mineral species corundum. As already explained, -the difference in color is due entirely to very slight traces of -chemical impurities. Frequently, the impurities are present in -irregular patches that give spotty color effects.</p> -<p>Some mineral species possess many of the desirable qualities -of gemstones yet cannot be used as gems because they are -chemically active and therefore are less durable. They undergo -alteration and decomposition when exposed to light or to one -or another of such substances as air, water, skin acids and oils.</p> -<h2 id="c3"><span class="small">3</span> -<br />THE SHAPING OF GEMSTONES</h2> -<p>Gemstone crystals often have naturally brilliant, reflecting -faces, but rarely are they perfect and unblemished. Also, -their natural shapes do not provide the best expression of -their luster, brilliance, dispersion, color, and other inherent -properties. In fashioning a gemstone, the skilled artisan tries to -develop these hidden assets and to otherwise enhance the -gemstone’s general beauty.</p> -<p>From ancient times until the 1600’s little was attempted in -the way of shaping gemstones other than to smooth or polish -the natural form. Although similarly smoothed, or <i>tumbled</i>, gemstones -recently have returned to fashion, the finest pieces of -gem rough are now converted mainly into <i>faceted</i>, or shaped, -stones. Standard types of facets—the flat faces that are -ground and polished on the rough gem material—have been -given individual and group names. A typical example is the -<i>brilliant</i> cut, which is most commonly used to best bring out -the qualities of a diamond.</p> -<div class="pb" id="Page_11">11</div> -<div class="img" id="fig12"> -<img src="images/p09.jpg" alt="" width="500" height="416" /> -<p class="pcap">The standard brilliant cut, with a pattern of many -facets, is commonly used for gemstones having a -high refractive index and, therefore, great brilliance.</p> -</div> -<div class="img" id="fig13"> -<img src="images/p09a.jpg" alt="" width="316" height="800" /> -<p class="pcap">Characteristic of the standard -brilliant cut are the 32 crown -facets surrounding a relatively -small, flat, table facet and the 24 -pavilion facets and culet at the -bottom of the stone.</p> -</div> -<div class="img" id="fig14"> -<img src="images/p09d.jpg" alt="" width="308" height="800" /> -<p class="pcap">Ideal proportions for the standard brilliant cut -have been carefully determined so that the maximum -amount of light will be reflected back out the -top of the stone. Incorrect proportions cause the -light to be lost at the bottom of the stone.</p> -</div> -<div class="pb" id="Page_12">12</div> -<div class="img" id="fig15"> -<img src="images/p10.jpg" alt="" width="500" height="377" /> -<p class="pcap">The step cut, often called the emerald cut, frequently -is used for colored stones because the large -table permits a good view of the color.</p> -</div> -<div class="img" id="fig16"> -<img src="images/p10a.jpg" alt="" width="428" height="800" /> -<p class="pcap">The emerald or step cut provides a large table and -a full bottom for the stone. Although the number -of crown and pavilion facets may vary, the general -pattern is maintained.</p> -</div> -<div class="img" id="fig17"> -<img src="images/p10c.jpg" alt="" width="500" height="423" /> -<p class="pcap">The simplified English brilliant cut takes -maximum advantage of the strong dispersion of -diamond, with its flashes of fire, but the fewer facets -provide less sparkle than the standard brilliant cut.</p> -</div> -<p>The diagram shows a brilliant-cut diamond with angles and -facets arranged to give the stone maximum internal reflection -as well as to make use of its strong dispersive ability. Certain -of the light beams passing into a brilliant-cut diamond produce -colorless brilliance by being reflected back out of the stone -<span class="pb" id="Page_13">13</span> -through the <i>table</i> by which they entered. Other light beams, -emerging through inclined facets, are split up by dispersion -into the rainbow, or fire, effect so prized in diamonds. A stone -that has been cut too wide for its depth, with incorrect facet -angles, will look large for its weight but its brilliance and -fire will have been drastically reduced.</p> -<div class="img" id="fig18"> -<img src="images/p10d.jpg" alt="" width="342" height="800" /> -<p class="pcap">The English brilliant cut has 28 crown and pavilion -facets—28 fewer than the standard brilliant cut.</p> -</div> -<div class="img" id="fig19"> -<img src="images/p10f.jpg" alt="" width="436" height="800" /> -<p class="pcap">The Dutch rose cut is a very simple one that is -used mainly for small diamonds in jewelry that -features a larger, colored stone. It is based on a -form that originated in India and was introduced -through Venice.</p> -</div> -<p>For other purposes and for other kinds of precious stones a -number of basic cuts have been developed. The <i>brilliant</i> and <i>step</i> -cuts are by far the commonest of these basic cuts, but modern -jewelry design frequently uses such fancy cuts as the baguette, -cut-corner triangle, epaulet, half moon, hexagon, keystone, kite, -lozenge, marquise, pentagon, square, trapeze, and triangle. -Some of these are shown here.</p> -<div class="pb" id="Page_14">14</div> -<div class="img" id="fig20"> -<img src="images/p11.jpg" alt="" width="500" height="499" /> -<p class="pcap">Just as the English brilliant cut, because of its 28 -fewer facets, has less sparkle than the standard -brilliant cut, the step brilliant, with its 20 additional -facets, has greater sparkle.</p> -</div> -<div class="img" id="fig21"> -<img src="images/p11a.jpg" alt="" width="351" height="799" /> -<p class="pcap">The step brilliant cut is a complicated modification -of the standard brilliant. With an additional 12 -facets in the crown and 8 in the pavilion, the step -brilliant has 78 facets, compared with the 58 of -the standard.</p> -</div> -<div class="img" id="fig22"> -<img src="images/p11f.jpg" alt="" width="600" height="716" /> -<p class="pcap">Various kinds of cuts have been -devised for special purposes in -jewelry design. These include the -pentagon (1), lozenge (2), hexagon -(3), cut-corner triangle (4), -kite (5), keystone (6), epaulet -(7), baguette (8), trapeze (9) -and square (10).</p> -</div> -<div class="pb" id="Page_15">15</div> -<div class="img" id="fig23"> -<img src="images/p11g.jpg" alt="" width="800" height="669" /> -<p class="pcap">With this typical trim saw, water is used as a coolant for the rapidly -rotating metal disk, which has a diamond-impregnated rim. Here, -the blade is cutting its way through a piece of gem tourmaline.</p> -</div> -<p>In general, there are three operations in preparing a gemstone -from the rough—sawing, grinding, and polishing. Sawing -usually is accomplished by using a thin, diamond-impregnated, -rapidly rotating disk of soft iron or bronze, with oil or water -being used as a coolant. The very hard diamond dust literally -scratches its way through the stone. Once the stone is sawed to -shape, the facets are ground and polished on a rotating horizontal -disk by the use of various abrasives. For rough grinding, -<span class="pb" id="Page_16">16</span> -silicon carbide—or sometimes diamond powder—is used. -Scratches are removed and a high polish is given by the use of -tin oxide, pumice, rouge, or other fine-grained abrasives. The -thick disks, or laps, are made of cast iron, copper, lead, pewter, -wood, cloth, leather, and certain other materials. Since each -species of gemstone differs in its characteristics, each must be -treated somewhat differently as to sawing and lapping speeds, -kind of lap, and choice of abrasives. Because of the greatly -increased interest in gem cutting as a hobby and the large -number of amateur cutters, a substantial market has developed -in the United States for lapidary supplies and equipment. New -kinds of machinery, new abrasives, and new kinds of saws and -laps are introduced regularly. Fundamentally, however, the -process still involves sawing, grinding, and polishing.</p> -<div class="img" id="fig24"> -<img src="images/p12.jpg" alt="" width="800" height="678" /> -<p class="pcap">The final step in preparing a gemstone from rough is the applying -of a high polish by pressing the stone against a rotating disk that -has an extremely fine abrasive on its surface. Here, the disk is of -felt, and the abrasive is tin oxide.</p> -</div> -<div class="pb" id="Page_17">17</div> -<div class="img" id="fig25"> -<img src="images/p12a.jpg" alt="" width="688" height="799" /> -<p class="pcap">The cabochon cut gets its name -from the French word “caboche,” -meaning pate or knob, a reference -to the rounded top of the stone. -Here, from top to bottom, beginning -at left, are cabochons of -turquoise, agate, and petrified -wood; jasper, smithsonite, and williamsite; -and amazonite, petoskey -stone, and carnelian. (Two-thirds -actual size.)</p> -</div> -<div class="img" id="fig26"> -<img src="images/p12b.jpg" alt="" width="800" height="536" /> -<p class="pcap">These exquisite bowls, measuring -2 to 3 inches across, are part of a -set of 35 carved by George Ashley -of Pala, Calif., from gem materials -found in the United States. Left -to right: paisley agate from California, -petrified wood from Arizona, -black jade from Wyoming, -chrysocolla from Arizona, and -variscite from Utah. (One-third -actual size.)</p> -</div> -<div class="pb" id="Page_18">18</div> -<p>Shaping of gemstones is not limited to geometric faceting. -Many stones, especially those which are opaque or which produce -stars and cat’s-eyes, are cut as <i>cabochons</i>. This ancient, and -probably oldest, cutting style consists merely of a raised and -rounded form. When extended completely around the stone, -the cabochon form results in a bead that can be drilled and -strung. Many cabochons, especially those of less expensive gem -materials, are now cut in large quantities to standard sizes in -order to fit mass-produced gem mountings.</p> -<p>Sculpting in gemstones is a much more intricate, nongeometric -kind of shaping. Although tools differ in detail, and the -gem sculptor must possess an artistic eye as well as lapidary -skill, the basic processes of sawing, grinding, and polishing -are the same.</p> -<div class="img" id="fig27"> -<img src="images/p13.jpg" alt="" width="288" height="801" /> -<p class="pcap">This coral carving, 11 inches tall -without the stand, owes its thin, -graceful, willowy shape to the skill -of the artist in following the contour -of a natural coral branch.</p> -</div> -<div class="pb" id="Page_19">19</div> -<div class="img" id="fig28"> -<img src="images/p13a.jpg" alt="" width="623" height="800" /> -<p class="pcap">The contemporary sculptor Oskar -III J. W. Hansen visualized and -created the likeness of a spirited -stallion in this 4½-inch turquoise -carving, a gift of George Gilmer.</p> -</div> -<div class="img" id="fig29"> -<img src="images/p13b.jpg" alt="" width="700" height="675" /> -<p class="pcap">This world-famed crystal ball, -given to the Collection as a memorial -to W. R. Warner by his -widow, represents another phase -of the lapidary art. Cut from a -block of Burmese quartz estimated -to weigh 1000 pounds, this extremely -valuable, flawless, colorless -sphere has a diameter of 12⅝ -inches and weighs 106¾ pounds.</p> -</div> -<div class="pb" id="Page_20">20</div> -<h2 id="c4"><span class="small">4</span> -<br />GEM SUBSTITUTES</h2> -<p>Because of their rarity and relatively high cost, the number of -real gems used throughout recorded times must be insignificant -compared to the number of gem substitutes used. -There are records of glass and ceramic imitations of gems as -early as 3000 B.C. Certainly, the world gem markets today -are flooded with man-made gems. There even has been developed -a laboratory process for growing a coating of synthetic emerald -on the surface of a faceted stone of natural colorless beryl. -The recut gem looks like a natural emerald, and it has natural -inclusions that totally synthetic emeralds lack.</p> -<p>In general, gem substitutes can be classified as imitation -stones, assembled stones, reconstructed and altered stones, and -synthetic stones.</p> -<h3>IMITATION STONES</h3> -<p>Any material will serve as an imitation of a natural gem -as long as it resembles the real thing under casual -examination. Because of the great variety in types and colors -available, glass and plastics are the most commonly used -materials for making imitation gems. Almost every gem has -been simulated effectively. The substitutes offer no difficulty -of identification to the expert, but many are deceptive to the -layman.</p> -<div class="pb" id="Page_21">21</div> -<h3>ASSEMBLED STONES</h3> -<p>It has been the practice for centuries to -build up gemstones by fusing or cementing -a shaped piece of natural -gemstone to another piece, or other -pieces, of inferior or artificial material.</p> -<p>A colorless common beryl crown cemented -to a pavilion of green glass produces -an emerald doublet—part natural, -part artificial—of good color and high -durability. A thin piece of beautifully -colored opal cemented to a base of inferior -opal provides an assembled stone -that looks like a thick piece of high-quality -opal. Triplets, and even stones -in which there are pockets of colored -liquids or metal foil between the -shaped pieces, are known.</p> -<p>Usually, assembled stones are easily -detected, since the joint will show -under magnification, but sometimes -they are mounted in settings that -obscure the joint, and detection is -more difficult.</p> -<div class="img" id="fig30"> -<img src="images/p14.jpg" alt="" width="296" height="600" /> -<p class="pcap">Assembled imitation gemstones. If it were measured -on its natural ruby table, the assembled stone shown -at top would have all the characteristics of a large -ruby, including refractive index. The color of the -quartz and glass combination (middle) depends on -the color of the liquid in the cavity. Since emerald -is green beryl, an inexpensive colorless beryl sandwich -of green glass (bottom) would appear to be -an expensive emerald. The joints of assembled -stones often are hidden in the jewelry mountings.</p> -</div> -<div class="pb" id="Page_22">22</div> -<h3>RECONSTRUCTED AND ALTERED STONES</h3> -<p>Ruby fragments may be heated at high temperature to -partially melt them into a large mass that can be cut into -a more valuable stone. Ruby is the only stone that can be -successfully reconstituted in this way, but there are many -other ways of tampering with natural stones to make them -more desirable.</p> -<p>Sometimes natural stones are backed with foil or a metallic -coating to enhance their color, to provide brilliance, or to produce -a star effect. It is said that in an inventory of the Russian -crown jewels by the Soviet Government, the ruby-colored -Paul the First Diamond was discovered to be a pale pink -diamond backed by red foil. Today, some diamonds are coated -on the back with a blue film to improve their color.</p> -<p>Aquamarine, when pale greenish blue, may be heated in -order to deepen the blue color, and poorly colored amethyst -may be heated to produce a beautiful yellow-brown quartz, -called citrine, that often is misrepresented as topaz. By strong -heating, the brown and reddish brown colors of zircon can be -changed to blue or colorless, both of which states are unknown -in natural zircon. Dyes, plastics, and oils are used to impregnate -porous gems such as turquoise and variscite, and even jade. -Off-color diamonds, when exposed to strong atomic radiation, -can be changed to attractive green, brown, and yellow colors, -causing them to resemble higher-priced <i>fancies</i>.</p> -<p>In the constant search for something new, gem suppliers -sometimes introduce into gemstones colors that are not always -an improvement. For example, the beautiful purple of some -amethyst can be converted, by heat treatment, to a peculiar -green. Such an altered stone is marketed as <i>greened amethyst</i>.</p> -<p>All of this tampering with gemstones complicates the problem -of identification, so it is a matter of serious concern to the -gem trade.</p> -<div class="pb" id="Page_23">23</div> -<h3>SYNTHETIC STONES</h3> -<p>For over 200 years mineralogists have been devising techniques -for producing synthetic minerals in the laboratory, -and attempts have been made, sometimes with considerable -success, to apply these techniques to the production of synthetic -gemstones. To qualify as a synthetic gemstone the man-made -product must be identical chemically and structurally with its -natural counterpart. Sapphire, ruby, spinel, emerald, and -rutile in gem quality have been brought to commercial -production.</p> -<p>Two of the basic techniques used in producing synthetic -gems are the <i>flame-fusion</i> and the <i>hydrothermal</i> processes.</p> -<div class="img" id="fig31"> -<img src="images/p15.jpg" alt="" width="279" height="800" /> -<p class="pcap">The Verneuil furnace, for making synthetic -gem rough. A mixture of hydrogen -(H) and oxygen (O) burns almost explosively, -heating the fusion chamber (F) -to high temperatures. For example, -powdered aluminum oxide and coloring -agents are sifted down from hopper (A) -to the fusion chamber and form a cylindrical -boule (B) on an adjustable stand -(C).</p> -</div> -<p>In the flame-fusion process—invented in 1904 -by the French chemist Verneuil—powdered -aluminum oxide, containing coloring agents, is -sieved down through the flame of a vertical -blowtorch furnace. As it passes through the -flame, the powder melts and accumulates as -drops on an adjustable stand just below the -flame, where it forms a single crystal <i>boule</i> of -the synthetic rough. In a few hours a boule of -several hundred carats can be formed. When -such furnaces are operated in banks of several -hundred units, the commercial production of -<span class="pb" id="Page_24">24</span> -corundum alone becomes possible at the rate of many tons a -year. Through the years, of course, refinements have been made -on Verneuil’s original furnace.</p> -<p>In the hydrothermal process, which differs greatly from -Verneuil’s flame-fusion process, crystals are grown from solutions -of the raw materials that have been subjected to varying -conditions of very high pressure and temperature. Some of the -quartz used for electronics purposes also is manufactured in -this way.</p> -<p>Since chemical composition and crystal structure are the -basic characteristics by which a gemstone is identified, and -these characteristics are identical in both the manufactured -stone and its natural counterpart, the synthetic gemstones -offer a very serious challenge to those concerned with gem -identification.</p> -<h2 id="c5"><span class="small">5</span> -<br />GEM LORE</h2> -<p>All sorts of magic and symbolic properties have been -ascribed to gemstones through the ages; for example, the -cat’s-eye has been prescribed as a cure for paleness, citrine -has been worn as a protection from danger, and the opal -cherished as the symbol of hope. The result has been the -creation of an intricate, chaotic, and contradictory but interesting -mass of gem lore.</p> -<p>Among the treasures in the Smithsonian’s Museum of Natural -History is a very old silver breastplate that once was in an -ancient synagogue and supposedly was modeled after the one -worn by Aaron, the first high priest of the Hebrews. In this -<span class="pb" id="Page_25">25</span> -plate are mounted twelve stones representing the Twelve -Tribes of Israel. Among Christians, the Twelve Apostles also -were represented symbolically by precious stones.</p> -<dl class="undent"><dt class="center">THE TWELVE TRIBES</dt> -<dt>Levi, <i>Garnet</i></dt> -<dt>Zebulon, <i>Diamond</i></dt> -<dt>Gad, <i>Amethyst</i></dt> -<dt>Benjamin, <i>Jasper</i></dt> -<dt>Simeon, <i>Chrysolite</i></dt> -<dt>Issachar, <i>Sapphire</i></dt> -<dt>Naphtali, <i>Agate</i></dt> -<dt>Joseph, <i>Onyx</i></dt> -<dt>Reuben, <i>Sard</i></dt> -<dt>Judah, <i>Emerald</i></dt> -<dt>Dan, <i>Topaz</i></dt> -<dt>Asher, <i>Beryl</i></dt></dl> -<dl class="undent"><dt class="center">THE TWELVE APOSTLES</dt> -<dt>Peter, <i>Jasper</i></dt> -<dt>Andrew, <i>Sapphire</i></dt> -<dt>James, <i>Chalcedony</i></dt> -<dt>John, <i>Emerald</i></dt> -<dt>Philip, <i>Sardonyx</i></dt> -<dt>Bartholomew, <i>Sard</i></dt> -<dt>Matthew, <i>Chrysolite</i></dt> -<dt>Thomas, <i>Beryl</i></dt> -<dt>James the Less, <i>Topaz</i></dt> -<dt>Jude, <i>Chrysoprase</i></dt> -<dt>Simon, <i>Hyacinth</i></dt> -<dt>Judas, <i>Amethyst</i></dt></dl> -<p>The number “12” seems to follow a chain of gemstone -superstitions. Gemstones were considered to have mystical -relationship not only with the Twelve Tribes and the Twelve -Apostles but also with the Twelve Angels, the Twelve Ranks -of the Devil, and the Twelve Parts of the human body.</p> -<p>Some stones were even endowed with astrological significance -and were believed to be in sympathy with the twelve -zodiacal signs. On the basis of an elaborate system of prognostications, -an astrologer was considered able to foretell -future events by proper observance of changes in hue and -brilliance of the symbolic stones.</p> -<dl class="undent"><dt>Aries the Ram, <i>Bloodstone</i></dt> -<dt>Taurus the Bull, <i>Sapphire</i></dt> -<dt>Gemini the Twins, <i>Agate</i></dt> -<dt>Cancer the Crab, <i>Emerald</i></dt> -<dt>Leo the Lion, <i>Onyx</i></dt> -<dt>Virgo the Virgin, <i>Carnelian</i></dt> -<dt>Libra the Scales, <i>Chrysolite</i></dt> -<dt>Scorpio the Scorpion, <i>Aquamarine</i></dt> -<dt>Sagittarius the Archer, <i>Topaz</i></dt> -<dt>Capricornus the Goat, <i>Ruby</i></dt> -<dt>Aquarius the Water Bearer, <i>Garnet</i></dt> -<dt>Pisces the Fishes, <i>Amethyst</i></dt></dl> -<p>Perhaps in our own space-oriented times the ancient superstitions -sympathetically relating certain gemstones with the -<span class="pb" id="Page_26">26</span> -planets will be revived. In the distant past, -moonstone, topaz, and other white stones were -believed to be in sympathy with the Moon, -diamond and ruby with the Sun, jasper and -emerald with Mars, amethyst, topaz, and -emerald with Venus, carnelian, topaz, and -amethyst with Jupiter, turquoise and sapphire -with Saturn, and rock crystal, agate, and emerald -with Mercury. Since Uranus, Neptune, and -Pluto were unknown to the ancients, these -planets have not been represented by gemstones.</p> -<p>Of special interest to the American public -are birthstones. Many birthstone lists have -been proposed, and in order to use this idea to -popularize gemstones the American jewelry -industry has agreed upon an official list. This -list has served to bring about some uniformity -in the selection of birthstones for the twelve -months.</p> -<dl class="undent"><dt>January, <i>Garnet</i></dt> -<dt>February, <i>Amethyst</i></dt> -<dt>March, <i>Aquamarine</i> or <i>Bloodstone</i></dt> -<dt>April, <i>Diamond</i></dt> -<dt>May, <i>Emerald</i></dt> -<dt>June, <i>Moonstone</i> or <i>Pearl</i></dt> -<dt>July, <i>Ruby</i></dt> -<dt>August, <i>Peridot</i> or <i>Sardonyx</i></dt> -<dt>September, <i>Sapphire</i></dt> -<dt>October, Opal or <i>Tourmaline</i></dt> -<dt>November, <i>Topaz</i> or <i>Citrine</i></dt> -<dt>December, <i>Turquoise</i> or <i>Lapis lazuli</i></dt></dl> -<p>All these associations and strange beliefs -have served to create in the general public a -mental image of gemstones that gives to them -an increased exoticism and mysterious appeal -far exceeding their monetary value.</p> -<div class="img"> -<img src="images/p16.jpg" alt="{zodiac symbols}" width="600" height="424" /> -</div> -<div class="pb" id="Page_27">27</div> -<h2 id="c6"><span class="small">6</span> -<br />PRINCIPAL GEM SPECIES</h2> -<p>An excursion into the literature of gems would reveal that -there is much to be discovered about them other than the -cold facts of gemology, techniques of gem cutting, and -tales of gem lore. When all the information about an individual -species is assembled, it provides a sketch of a fascinating gemstone -personality. Whole books have been written about -diamond—books filled with essays on its mining history, -natural occurrences, scientific significance, and best known -cut stones.</p> -<p>In the following sections of this book, some of the facts about -several of the better known gem species have been gathered. -The treatment is not meant to be complete, but enough information -is given so that the Museum visitor may better understand -and remember what he has seen.</p> -<p>For each species described there are color illustrations of -certain gemstones displayed in the collection. Several photographic -and artistic techniques have been used to emphasize -the various aspects of the beauty of these stones, many of which -are the largest and finest of their kinds known; however, not all -of the finest gems are pictured here.</p> -<p>At the end of this descriptive section is a list of the significant -faceted gemstones in the collection. Obviously, this list -will change, because new gemstones constantly are being -acquired.</p> -<div class="pb" id="Page_28">28</div> -<h3>DIAMOND</h3> -<p>Diamond is the king of gems. It is a form of pure carbon, -and it is the hardest substance known; only diamond will -cut diamond. It is interesting that the humble graphite, -its close relative, is also pure carbon, but graphite is so soft -that it is used as a lubricant and for making the “lead” in -pencils.</p> -<p>The ancients believed diamond to be indestructible, and -even today many people believe that diamond cannot be broken. -Despite its great hardness, however, diamond is not exceptionally -tough, and it can be split along what diamond cutters -call its <i>grain</i>.</p> -<p>The diamond’s high brilliance results from its very high -refraction, or ability to bend light, and its fire is caused by its -high dispersion, or ability to divide light into its rainbow -colors. However, only in properly cut stones are diamond’s -brilliance and fire developed to their maximum.</p> -<p>At great depths in the crust of the earth and under conditions -of very high pressure and temperature, diamonds form in pipe-like -bodies of kimberlite, a heavy dark rock consisting primarily -of two minerals, pyroxene and olivine. In South Africa -diamonds are mined from the kimberlite, but they also are -recovered there and elsewhere from beds of sand and gravel -where they have accumulated after being released from their -mother rock by erosion.</p> -<p>The world’s largest diamond deposits are in Africa, and -names such as Congo, Sierra Leone, and the Union of South -Africa bring to mind colorful legends of fabulous discoveries of -diamond. Smaller deposits are found in South America—in -Brazil, British Guiana, and Venezuela—and in Asia. Even in -the United States some diamonds have been found.</p> -<p>India was the most important source of diamond until 1728, -when discoveries were made in Brazil. Among the important -large diamonds found in India were the Koh-i-noor, the Great -<span class="pb" id="Page_29">29</span> -Mogul, and, very likely, the Hope Diamond. Like India, Brazil -in turn declined as a major source of diamond with the discovery -and efficient recovery of large quantities in South Africa.</p> -<div class="img" id="fig32"> -<img src="images/p17.jpg" alt="" width="700" height="596" /> -<p class="pcap">The Hope Diamond, because of its long and dramatic history and its -rare deep-blue color, is probably the best known diamond in the -world. By speculation, the Hope is linked to the famous “French -Blue,” which was brought to France from India in 1668 to become -part of the crown jewels of Louis XIV. The French Blue was stolen -in 1792 and never recovered, but in 1830 an extraordinary 44.5-carat -blue diamond—presumably cut from the missing gem—came on the -market. It was purchased by Henry Thomas Hope of England and -became known by its present name. In 1949 the gem was acquired -from the estate of Mrs. Evalyn Walsh McLean by Harry Winston -Inc., of New York. Ten years later, Harry Winston, Inc., presented -the gem (shown here in actual size) to the Smithsonian Institution.</p> -</div> -<p>Diamonds are extremely rare even in diamond mines. For -example, the famous South African mines contain only one part -of diamond in more than 14 million parts of worthless rock. -In spite of this, more than three tons of gem- and industrial-quality -diamond were mined in 1963.</p> -<p>Among the British crown jewels is a cut diamond weighing -530.20 carats (more than 3¾ ounces), one of several stones -that were cut from the largest gem diamond ever discovered. -<span class="pb" id="Page_30">30</span> -The rough stone, known as the Cullinan Diamond, -weighed 3106 carats (almost 1¾ pounds) when it was found -at the Premier Mine in South Africa in 1905.</p> -<div class="img" id="fig33"> -<img src="images/p18.jpg" alt="" width="700" height="566" /> -<p class="pcap">The Portuguese Diamond, weighing 127 carats, is the 13th largest cut -diamond on record. More unusual, it is from Brazil, and is thought to have -been part of the Portuguese crown jewels. In addition to its brilliant color -flashes, it has a slight milky fluorescence that causes it to “glow” even in -artificial light. (Actual size.)</p> -</div> -<p>Diamonds vary from colorless to black and from transparent -to opaque. As they come from the mines, they are -graded into two groups, gem and industrial. Those whose -color, imperfection, or shape make them useless as gems—more -than 8 out of every 10 carats mined—are used in industry. -Diamonds of industrial quality also are produced synthetically, -and these are used primarily in the manufacture of grinding -wheels.</p> -<p>The best gem diamonds are flawless and are colorless or -slightly blue. Their value depends on their color, clarity, cut, -and carat weight. Most costly are those called fancies, which -have a distinct color such as blue, pink, green, or deep yellow.</p> -<div class="pb" id="Page_31">31</div> -<h3>PEARL</h3> -<p>Pearl is included among gemstones only because it is a -beautiful object used as jewelry. As has been noted, pearl -is not mineral because it is formed by the action of a living -organism. However, the pearl has long occupied an important -position among jewels, and it is unique in requiring no lapidary -art to enhance its beauty. Nature has perfected pearls.</p> -<div class="img" id="fig34"> -<img src="images/p18a.jpg" alt="" width="700" height="763" /> -<p class="pcap">The strand of matched pearls was -presented to President Van Buren -by the Imam of Muscat. The three -baroque (irregularly shaped) -pearls are freshwater pearls from -the Wabash River in Indiana.</p> -</div> -<p>The ancient Chinese believed that pearls originated in the -brain of a dragon. We now know, of course, that pearl is -created by a secretion of a mollusk. Very few mollusks have the -ability to produce the fine mother-of-pearl used in the jewelry -trade, and even among those that can, very few produce pearls -with iridescence, or <i>orient</i>, as it is known in the trade. Only -two genera, the pearl oyster (<i>Margaritifera</i>) and the pearl -mussel (<i>Unio</i>) are important sources of the gem. Edible -<span class="pb" id="Page_32">32</span> -oysters rarely produce pearls, and when they do, the pearls are -of poor quality.</p> -<p>The shells of pearl-producing mollusks are composed of -layers of calcium carbonate in the form of either calcite or -aragonite. These layers, cemented together with an organic -substance known as conchiolin, are known as nacre. The layer -closest to the animal is deposited in tiny overlapping patches, -producing an iridescent effect caused by the interference of -light rays reflected from the plates making up the nacre. The -same material coats the surface of a gem pearl.</p> -<p>Seldom does a mollusk live out its time without attack by -creatures boring through its shell, or without intrusion through -the normal shell opening of tiny parasitic worms, sand, or -other irritants. Usually inert particles are forced against the -inside of the shell, where they are covered with layers of pearl -that fasten them to the shell. This is the source of most <i>blister -pearls</i>. When the irritant remains in its fleshy part, the mollusk -deposits a protective shell of pearl to cover it completely, and a -spherical pearl may result. Pearls of less-symmetrical shape, -called <i>baroques</i>, are more common.</p> -<p>The value of a pearl depends on its shape, color, orient, and -size. Pearls of highest value are white with a faint tinge of -pink or yellow, possess fine orient, are round, and are free of -surface blemishes. The grading of pearls for color requires considerable -experience to detect delicate differences. Various -classification names, such as “rosée” for delicate pink shades, -are used. Fancy colored pearls are those with a strong yellow, -bronze, pink, green, blue, or black color. Grading for shapes, -which differ markedly, is easier. Spherical pearls are usually -drilled for beads; pear-shaped or drop pearls are used in earrings -and pendants; and “boutons” or button-shaped pearls, with -one flat side, are used for ear ornaments, cuff links, and rings. -Irregular, baroque pearls and tiny seed pearls are used in -jewelry designs with noble metals and perhaps other gemstones.</p> -<p>The world’s finest pearls, called <i>oriental pearls</i>, come from the -fisheries of the Persian Gulf. Fine pearls also are found off the -coasts of Burma, Tahiti, New Guinea, Borneo, Venezuela and -western South America, and in the Gulf of California. Fresh-water -<span class="pb" id="Page_33">33</span> -pearls of high quality, formed in pearl mussels, are found -in various rivers in Europe and the United States, especially in -rivers in the Mississippi Valley.</p> -<p>A method of growing <i>cultured pearls</i> has been well developed. -A mother-of-pearl bead is inserted in the oyster as an irritant, -and the animal is replaced in the sea in a cage. When oysters -so treated are recovered after a period of three to seven years, -the beads in the harvested crop usually are found to be coated -with a layer of nacre up to almost a sixteenth of an inch thick.</p> -<p>The cultured pearl can be identified only by the observance—through -a drill-hole or by X-ray—of the mother-of-pearl core, -which had been inserted in the oyster. An instrument called -an endoscope, devised for rapid testing of drilled pearls, -relies on a beam of strong light carried by a hollow needle. -The needle is inserted into the drill hole, and as it passes -through the center portion of a natural pearl a flash of light, -reflected through a mirror system in the needle, is observed.</p> -<h3>CORUNDUM -<br /><span class="smaller">(RUBY AND SAPPHIRE)</span></h3> -<p>Both <i>ruby</i> and <i>sapphire</i>, which are second only to diamond in -hardness, are of the mineral species corundum, an oxide of -aluminum. They are identical in all characteristics except -color. Most corundum is opaque, and it is mined in large -quantities for use as an abrasive. In a few places, such as -Moguk in Upper Burma and in Ceylon, clear corundum is -found that is suitable for use as a gem.</p> -<p>Red corundum is known as ruby. Its color, caused by traces -of chromium, ranges from rose through carmine to a dark -purplish red referred to as pigeon’s blood red. Rubies of this -very desirable latter color often are called Burma rubies, and -they are the most costly of all the corundum gems.</p> -<p>All gem corundum having a color other than red is sapphire. -The name sapphire means blue, and this is the color most frequently -associated with this gemstone. The finest sapphires are -a velvety cornflower blue, and they come from Kashmir. Blue, -<span class="pb" id="Page_34">34</span> -white, yellow, gold, pink, and all the other colors of corundum -are caused by the presence of slight traces of iron, chromium, -titanium, and other metals present as dissolved impurities in -the aluminum oxide. Frequently sapphires are found that show -patches of blue and yellow, or that have alternating zones of -red and blue. Pure corundum is colorless.</p> -<div class="img" id="fig35"> -<img src="images/p19.jpg" alt="" width="566" height="800" /> -<p class="pcap">A piece of uncut ruby, -from Burma, and five -small rubies of about -half a carat each, from -Ceylon. All have the -classic “pigeon’s blood” -color. (Actual size.)</p> -</div> -<p>Most gem corundum comes from the Orient, at localities such -as Moguk in Upper Burma, near Bangkok in Thailand, Kashmir -in India, and Ceylon. Because of this primarily Asian origin, the -word <i>oriental</i> often is used with the names of other gems to -denote a sapphire of a particular color. For example, green -sapphire sometimes is called oriental emerald, and the yellow -sapphire sometimes is called oriental topaz.</p> -<div class="pb" id="Page_35">35</div> -<div class="img" id="fig36"> -<img src="images/p19a.jpg" alt="" width="800" height="553" /> -<p class="pcap">The sapphires in this group vary in color from deep blue to gold, -and they come from widely separated localities. The scatter of small -multicolored stones came from Montana, and the magnificent 93-carat -golden sapphire, encircled by the gold bracelet, came from Burma. -(Slightly less than half actual size.)</p> -</div> -<p>There are some notable exceptions to the generally oriental -occurrence of corundum. Some good-quality ruby has been -found in North Carolina, and sapphire of many colors has come -from Montana.</p> -<p>During the formation of a corundum crystal, extremely -small needle-like inclusions of rutile sometimes occur in the -hexagonal pattern of the host crystal. When such inclusions -are arranged in this way by nature, they cause, in properly -cut stones, internal reflections that produce the optical phenomenon -known as asterism. The effect is that of a 6-rayed -star, and the gems in which asterism occurs are known as star -sapphires and star rubies. Asterism is rarer in ruby.</p> -<div class="pb" id="Page_36">36</div> -<div class="img" id="fig37"> -<img src="images/p20.jpg" alt="" width="800" height="675" /> -<p class="pcap">The Star of Asia, weighing -330 carats, is one of the -finest star sapphires in the -world. It is of a clear, deep -blue color and has a strong, -sharply defined, 6-rayed -star. (Actual size.)</p> -</div> -<div class="img" id="fig38"> -<img src="images/p20a.jpg" alt="" width="389" height="600" /> -<p class="pcap">Cutting a star stone requires -careful attention to -the directions in which the -cuts are to be made. Failure -to align the stone properly -with the axis of the crystal -will produce a stone with -an off-center, crooked, or -dim star, or may even -eliminate the star completely.</p> -</div> -<dl class="undent pcap"><dt>CRYSTAL AXIS</dt> -<dt>POSITION STONE MUST TAKE TO SHOW STAR</dt> -<dt>OTHER STAR STONES MAY BE CUT, BUT MUST BE IN THE SAME POSITION WITHIN THE CRYSTAL</dt> -<dt>ROUGH SAPPHIRE CRYSTAL</dt> -<dt>CRYSTAL AXIS</dt></dl> -<p>Since corundum is easily -manufactured, synthetic ruby -and sapphire are used extensively -in jewelry. The synthetic -stones can be distinguished from -natural stones by microscopic -examination of the kinds of inclusions -and internal defects.</p> -<dl class="undent"><dt>VARIETIES</dt> -<dd>Ruby: Red.</dd> -<dd>Sapphire: Blue, yellow, pink, green, colorless, and any color except red.</dd> -<dd>Star sapphire: Colored as sapphire and showing asterism.</dd> -<dd>Star ruby: Red and showing asterism.</dd></dl> -<div class="pb" id="Page_37">37</div> -<h3>BERYL -<br /><span class="smaller">(INCLUDES EMERALD AND AQUAMARINE)</span></h3> -<p>Beryl is probably the most widely used colored gemstone, -and under its several names in the gem world it is probably -the best known. When it is a rich green it is known as -<i>emerald</i>, and when it is the blue-green of sea water it is called -<i>aquamarine</i>. Varieties such as the rose-pink <i>morganite</i>, golden-yellow -<i>heliodor</i>, and colorless <i>goshenite</i> are less well known than -emerald and aquamarine but are equally attractive and satisfactory -gemstones.</p> -<p>Beryl is beryllium aluminum silicate. It frequently occurs in -well-formed hexagonal crystals, and its many colors result -from the presence of very small percentages of several different -elements. Emerald owes its rich green color to traces of -chromium, and the detection of this element is one of the means -of identifying true emerald. Aquamarine, comprising the green -and blue-green beryls, gets its color mainly from traces of -iron. Practically all of the deep blue aquamarine available in -jewelry stores results from the heat treating of greenish beryl -or certain yellow-brown beryls. The stones are heated carefully -to about 800° F., and the color change is permanent. The -element lithium accounts for the color of pink beryl. As with -aquamarine, the color of yellow beryl is now considered to -be the result of traces of iron rather than uranium, as previously -thought. Pure beryl is colorless.</p> -<p>Beryl usually is found in pegmatites, which are very coarse-grained -granite rocks formed by the cooling of molten material -far beneath the earth’s surface. As the rock cools and beryl and -other crystals are formed, the stresses introduced are so great -that the crystals frequently shatter so badly they are useless as -gem material. Frequently, too, impurities are introduced during -crystal formation, and consequently the gem materials are found -only where the crystals were able to form without interference—such -as in openings or cavities in the rock.</p> -<p>Tremendous beryl crystals weighing as much as several tons, -but not of gem quality, have been discovered in a few localities. -<span class="pb" id="Page_38">38</span> -Large crystals of gem quality also occur in nature, and large -cut stones of aquamarine and other colors of beryl are relatively -common. Among the fine examples of beryl in the National -Gem Collection is a remarkably large (2054-carat), flawless -cut stone of rich yellow-green. This gem and others in the -collection weighing 1363 carats, 1000 carats, 914 carats, and -578 carats accentuate the occurrence of large gem crystals of -beryl in Brazil.</p> -<div class="img" id="fig39"> -<img src="images/p21.jpg" alt="" width="800" height="560" /> -<p class="pcap">Four large cut stones, all from Brazil, illustrate the color range of -beryl. Top, a 578-carat green beryl; left, a 235-carat morganite, -gift of Mr. and Mrs. Frank Ix, Jr.; bottom, a 133-carat gold beryl; -and, right, a 187-carat aquamarine. (Half actual size.)</p> -</div> -<p>The finest emeralds are not found in pegmatites. At Muzo -in Colombia, the most prolific source of the finest emeralds, -they occur in veins with calcite, quartz, dolomite, and pyrite. -The veins cut through dark-colored, carbonaceous limestone -and shale. Mining at Muzo began 350 years ago and still -continues sporadically to meet market requirements. Russian -emeralds occur as good-sized crystals in mica schist, a -metamorphic rock. They occur there with chrysoberyl, phenakite, -and common beryl. Some of the smaller stones have good -color and have been cut into valuable gems. Brazil, which -<span class="pb" id="Page_39">39</span> -produces many extraordinary aquamarines and other beryls, -has not produced quality emeralds. Periodically, over the -centuries, there have been reports of new discoveries of -emerald, but so far none of these has begun to rival the Muzo -source in either quantity or quality of the gems produced.</p> -<div class="img" id="fig40"> -<img src="images/p21a.jpg" alt="" width="800" height="562" /> -<p class="pcap">This tremendous golden beryl from Brazil, weighing 2054 carats, is -the largest cut beryl known of this color. Cut stones of this size that -contain no visible flaws or inclusions are most unusual. (Three-fifths -actual size.)</p> -</div> -<p>Although Brazil supplies the finest aquamarine and Colombia -the finest emerald, several localities in the United States are -sources of good-quality beryl of these colors. Foremost among -these localities are Maine, California, and Connecticut for -aquamarine and North Carolina for emerald. Morganite of pale -pink to deep peach color, from California, is also notable. -Various New England mines in Maine, New Hampshire, and -Connecticut and the gem mines of the Pala and Mesa Grande -districts of California have produced other colors of gem -beryl. However, most of the beryl mined in the United States -is used as an ore for beryllium, as little of it is of gem quality.</p> -<p>Because of its hardness (about 8), vitreous luster, beautiful -color, and rarity, emerald always has been highly prized as a -<span class="pb" id="Page_40">40</span> -gem. Fine-quality emeralds may be more costly than fine -diamonds. Other kinds of beryl have the same physical -properties as emerald, but since they are less rare their -relative value is lower.</p> -<p>Synthetic emerald of high gem quality has been marketed -successfully. A synthetic substitute for aquamarine is also -available; it is really a synthetic blue spinel.</p> -<dl class="undent"><dt>VARIETIES</dt> -<dd>Emerald: Grass green</dd> -<dd>Aquamarine: Blue green</dd> -<dd>Morganite: Pink</dd> -<dd>Heliodor: Yellow</dd> -<dd>Goshenite: Colorless</dd></dl> -<h3>TOPAZ</h3> -<div class="img" id="fig41"> -<img src="images/p22.jpg" alt="" width="481" height="800" /> -<p class="pcap">Three different cutting -styles and colors of topaz. -From top, a 235-carat colorless -stone from Colorado, -a 171-carat dark champagne-colored -stone from -Madagascar, and a 129-carat -sherry-colored stone -from Brazil. (Slightly less -than actual size.)</p> -</div> -<p>Because yellow is the most popular color of topaz it has -become customary to believe that all topaz is yellow. -Also, there is a tendency to believe that all yellow gemstones -are topaz. Neither -belief is correct. Stones of -yellow, sherry, blue, pink, -and colorless topaz all make -beautiful gems, and their -characteristics are identical -except for color. On the -other hand, citrine (a yellow -quartz), although entirely unrelated -to topaz, often is -disguised in the trade under -the names Brazilian topaz, -topaz quartz, or just topaz. -Great numbers of stones described and sold as yellow topaz really are the much commoner -citrine, which has few of the characteristics of fine topaz.</p> -<div class="pb" id="Page_41">41</div> -<div class="img" id="fig42"> -<img src="images/p22a.jpg" alt="" width="800" height="517" /> -<p class="pcap">A cushion-cut topaz from Brazil that weighs 1469 carats. It -is an odd shade of yellow-green.</p> -</div> -<div class="img" id="fig43"> -<img src="images/p22b.jpg" alt="" width="700" height="651" /> -<p class="pcap">A 3273-carat topaz of soft -blue that came from Brazil. The Smithsonian Institution had this -unique gem cut by Capt. John Sinkankas of California. For several -years it was the largest topaz in the collection. (Both gems are shown -in actual size.)</p> -</div> -<div class="pb" id="Page_42">42</div> -<p>Topaz, an aluminum fluosilicate, has a hardness of 8, a -vitreous luster, and a relatively high refractive index. It is -found in near-perfect crystals that range in size from very small -to very large, with some giants weighing as much as several -hundred pounds. Most of these crystals, especially the largest -ones, are colorless, a characteristic that indicates relatively -high purity of composition. Although topaz gems have little -fire, they take a high polish and can be very brilliant. Great -care must be taken in cutting and polishing topaz because of -its ready cleavage. The desired cut and high polish can be -secured by avoiding excessive heat or pressure during the -operation and by planning facets so that none lies exactly -parallel to the cleavage direction.</p> -<p>Although crystals of gem-quality topaz are found in many -localities, perhaps the splendid blue ones from Russia and -the yellow, wine, blue, and colorless ones from Brazil are best -known. Some fine topaz has been found in the United States -in such widely separated areas as New Hampshire, Texas, -Colorado, and California. The light, golden brown topaz from -Colorado has an unfortunate tendency to fade in strong sunlight. -It remains to be seen whether similar topaz coming -recently from comparable occurrences in Mexico also will -fade. By a system of heating and cooling, certain of the red-brown -topaz crystals from Ouro Preto, Brazil, can be converted -to colors ranging from salmon pink to purple red. Quick -heating to high temperatures can completely remove color, -and sudden or uneven cooling may cloud or crack the stone.</p> -<h3>OPAL</h3> -<p>Opal has been admired for its great beauty since ancient -times, but this gemstone lacked commercial appeal until -the discovery of the Australian black opal late in the -19th century.</p> -<div class="pb" id="Page_43">43</div> -<p>Opal is somewhat brittle, is sensitive to heat, and, in some -cases, tends to deteriorate despite the best of care. Therefore, -this stone lacks many of the physical characteristics required -for an ideal gem. These deficiencies would eliminate other -species from the list of gemstones, but the great beauty of its -flashing and shifting color patterns has made opal increasingly -popular. Even its name, coming from the ancient Sanskrit -“upala,” means precious stone.</p> -<p>With a hardness between 5½ and 6½, opal is the softest of -the more popular gems. It is sufficiently hard, however, to be -used in jewelry, where its setting usually helps to protect it -from shock and abrasion.</p> -<div class="img" id="fig44"> -<img src="images/p23.jpg" alt="" width="600" height="670" /> -<p class="pcap">Black opal, so called because the -color flashes appear against a dark -background, is found in Australia. -It is quite rare, and large pieces -such as the ones shown here -have become extremely valuable. -(Almost actual size.)</p> -</div> -<p>Opal is unlike most -gemstones in that its flashing -color is not due to the -color of the stone itself, or -even to the color of its included -impurities. Rather, -it is due to the way in -which tiny opal particles -are grouped during its formation. Detailed photographs taken -through an electron microscope show clearly how precious -opal is deposited as spheres that are so small they are indistinguishable -under powerful optical microscopes. These spheres -are packed together in very orderly networks, row upon row -and layer upon layer, with tiny open spaces, also in rows, -between them. Masses of common opal lack this orderly internal -arrangement of spheres. White light striking the precious -opal is reflected independently by each row of spheres, much -like the reflections from a series of slats in a venetian blind. -<span class="pb" id="Page_44">44</span> -Since these rows of spheres are spaced at -distances approximately the same as the -wavelength of light, a phenomenon known -as <i>diffraction</i> occurs. The separate reflections -interfere with each other in an -organized manner, cancelling out some -of the light wavelengths and reinforcing -others, producing color. The brilliant -color flashes are of different hues depending -on the sizes of the spheres of opal -and, therefore, the distances between rows. To provide the -best display of this optical effect, opal is almost always cut in -cabochon form rather than as faceted stones.</p> -<div class="img" id="fig45"> -<img src="images/p24.jpg" alt="" width="338" height="797" /> -<p class="pcap">Fire opals have rich fire; some have background -colors that vary from bright yellow through -orange and red; and some are colorless. Stones -such as the ones shown here, which weigh 7, -11, and 22 carats, have made Querétaro, Mexico, -famous as their source. (Actual size.)</p> -</div> -<div class="img" id="fig46"> -<img src="images/p24a.jpg" alt="" width="621" height="387" /> -<p class="pcap">This rare 34-carat opal from Brazil -resembles closely the opals found -in Australia. (Actual size.)</p> -</div> -<p>Common opal, which shows milky opalescence, does not -exhibit color flashes, and it is not used as a gemstone. Each of -the common varieties—such as hyalite, cacholong, and hydrophane—has -its own slightly different set of characteristics, -but only precious opal, with its dazzling color display, is -important for gem purposes. To take full advantage of the -small amounts of gem material available, or to bring out its -color better, <i>precious</i> opal is often cut as thin pieces and mounted -as doublets on some other backing. Also, the seams in rock -sometimes are cut so that the thin layer is exposed on a -<span class="pb" id="Page_45">45</span> -thicker backing of the adjoining rock. Precious opal, or gem -opal, is classified as <i>white opal</i> when the color flashes are in a -whitish or light background, <i>black opal</i> when the background -material is gray, blue-gray, or black, and <i>fire opal</i> when the -background is more translucent and red, reddish orange, or -reddish yellow.</p> -<p>Precious opal has been found in several areas of the world—in -nodules, in seams in rock, or as replacements of other -minerals or even of wood and shell. Hungarian deposits were -well known in Roman times, but these and other deposits -became insignificant with the discovery of opal in Australia -in the late 19th century. Opal deposits were discovered in -1889 at White Cliffs in New South Wales, and other important -discoveries in Australia followed, including deposits -at Lightning Ridge in New South Wales that produce very -dark stones and the rich fields of white opal at Coober Pedy -in South Australia. Mexico has remained for a long time the -principal source of richly colored fire opals, with the most important -deposits located in the state of Querétaro, where -mines have been worked intermittently since 1835. This has -made the town of Querétaro today the center for the trade -and cutting of Mexican opal.</p> -<dl class="undent"><dt>VARIETIES</dt> -<dd>White opal: Color flashes in light-colored background material</dd> -<dd>Black opal: Color flashes in dark gray or bluish background material</dd> -<dd>Fire opal: Orange or reddish background material</dd></dl> -<h3>SPINEL</h3> -<p>Two of the more famous stones in the British crown jewels -are the Black Prince’s Ruby and the Timur Ruby, but -neither of these stones is really ruby. Like the great red -gem in the crown that belonged to the Russian Empress -Catherine II, these two British stones are spinel. Although -spinel occurs in many colors, such as yellow, green, violet, -brown, and black, it is the red spinel that usually is seen in the -<span class="pb" id="Page_46">46</span> -gem trade. There are several varieties of red spinel, such as -<i>ruby spinel</i>, <i>balas ruby</i>, <i>rubicelle</i>, and <i>almandine spinel</i>—all of which -refer to the color resemblance to ruby.</p> -<div class="img" id="fig47"> -<img src="images/p25.jpg" alt="" width="800" height="579" /> -<p class="pcap">The hues and tints of spinel show subtle variations that are matched -only by those of tourmaline. Unlike tourmaline, however, spinel -may be bright ruby red. The cut stones curving around two pieces -of rough from Burma weigh (left to right) 30 carats (Ceylon), 34 -carats (Burma), 36 carats (Burma), 30 carats (Ceylon), and 22 carats -(Ceylon). (Three-fourths actual size.)</p> -</div> -<p>Spinel is an oxide of magnesium and aluminum, and it is not -related to ruby. However, because its hardness (8) is only -slightly less than that of ruby and its brilliance is about equal -to that of ruby, spinel makes an excellent substitute for that -gem. Also, because it is more plentiful, spinel costs much less. -It is interesting that red spinel, like ruby, gets its color from -the presence of traces of chromium.</p> -<p>Synthetic blue spinel is widely used as a substitute for -aquamarine, and synthetic spinels of other colors are used as -substitutes for many gems. However, the synthetic stones are -not ordinarily made in the subtle shades so characteristic of -natural spinel. Completely colorless spinel apparently exists -only as a synthetic material. Actually, because of its hardness, -durability, and many attractive colors, spinel makes a fine -gemstone in its own right.</p> -<div class="pb" id="Page_47">47</div> -<p>Like ruby and several other gemstones, spinel is found -chiefly in the gem gravels of Ceylon, Burma, and Thailand. -Appreciable amounts of spinel occur in the Ceylon gem gravels -as worn, rounded pebbles of many colors. In the Burmese -gravel deposits the spinel is often found as well-formed -octahedral crystals. Near Moguk, in Burma, spinel has been -found in its original position in the limestone rocks as well as -in the eroded stream deposits.</p> -<dl class="undent"><dt>VARIETIES</dt> -<dd>Almandine spinel: Purplish red</dd> -<dd>Rubicelle: Orange-red</dd> -<dd>Balas ruby: Rose red</dd> -<dd>Ruby spinel: Deep red</dd> -<dd>Chlorospinel: Translucent grass green</dd> -<dd>Ceylonite or pleonaste: Opaque dark green, brown, or black</dd> -<dd>Picotite or chrome spinel: Translucent dark yellow-brown or green-brown</dd></dl> -<h3>QUARTZ -<br /><span class="smaller">(INCLUDES ROCK CRYSTAL, AMETHYST, AND CITRINE)</span></h3> -<p>Few gemstones can compete with quartz for variety of color. -Having a hardness of 7 and occurring in many beautiful -varieties, only the relative abundance of quartz prevents -the species from attaining top rank among gemstones.</p> -<p>The two kinds of quartz, crystalline and cryptocrystalline -(fine-grained) quartz, occur in all kinds of mineral deposits -throughout the world. Much of this material is suitable for -cutting gems.</p> -<p>Colorless crystalline quartz, or <i>rock crystal</i>, makes attractive -faceted gems, and it is used as a suitable substitute for diamond -and zircon even though it lacks the fire and brilliance of those -gemstones. Some very large, flawless crystals of colorless -crystalline quartz have been found. The great Warner Crystal -Ball, with a diameter of 12⅞ inches and weighing 106¾ -pounds, was cut from such a crystal. In addition to the name -rock crystal, colorless crystalline quartz appears in the -jewelry trade under such names as rhinestone (not to be -confused with the glass substitute), Herkimer diamond (from -<span class="pb" id="Page_48">48</span> -Herkimer County, N. Y.), and Cape May diamond (from -Cape May, N. J.).</p> -<p>The most popular variety of quartz is <i>amethyst</i>, a transparent -form whose color ranges from pale violet to deep purple. In -many cut stones of amethyst the color intensity changes -sharply from section to section. This is due to irregular color -zoning common to amethyst crystals. The actual cause of the -purple color in amethyst is not very well understood. There are -fewer cut stones of amethyst in very large sizes because of the -rarity of large, flawless, well-colored crystals.</p> -<div class="img" id="fig48"> -<img src="images/p26.jpg" alt="" width="500" height="800" /> -<p class="pcap">This 4500-carat pale smoky quartz -egg from California rests on a gold -stand set with Montana sapphires. -The unique gem was cut and its -stand was designed and made by -Capt. John Sinkankas as a difficult -exercise in the lapidary art. -The quartz egg is 4 inches long -and almost 3 inches in diameter.</p> -</div> -<p>The name <i>citrine</i> (from the French word for lemon) attempts -to describe the yellow color of another variety of quartz. -Actually, the normal coloring of citrine varies from yellow to -red-orange and red-brown, -but the yellow -sometimes rivals the -yellow of topaz. In -addition to the normal -color range, the colors -of citrine may grade -through a grayish yellow -variety known as -<i>cairngorm</i> and a grayish -variety called <i>smoky -quartz</i> to a black variety -called <i>morion</i>. -Other varieties that -add color dimensions -to the group of quartz -<span class="pb" id="Page_49">49</span> -gemstones are <i>rose quartz</i> and <i>milky quartz</i>. Like amethyst, the -reason for the color in rose quartz has not been definitely -established. Milky quartz owes its color to myriads of tiny -cavities containing water or liquid carbon dioxide.</p> -<div class="img" id="fig49"> -<img src="images/p26a.jpg" alt="" width="800" height="607" /> -<p class="pcap">A 783-carat step-cut citrine of deep, rich color dwarfs a 278-carat -brilliant-cut citrine (at left), a 90-carat smoky quartz, and a 91-carat -briolette of citrine. The smoky quartz, from Switzerland, is -so dark that it appears to be opaque. The other three stones came -from Brazil. The briolette and brilliant-cut citrines were cut and -donated to the Smithsonian Institution by Albert R. Cutter. (Slightly -less than half actual size.)</p> -</div> -<p>The range of color in quartz is somewhat surprising, considering -that the mineral is a simple silicon dioxide. Some of -the colors, as with corundum and some other gemstones, are -due to traces of impurities. In quartz, these consist mainly of -oxides of iron, manganese, and titanium. However, all the -reasons for quartz coloration in its many varieties are not -known.</p> -<div class="pb" id="Page_50">50</div> -<div class="img" id="fig50"> -<img src="images/p27.jpg" alt="" width="575" height="800" /> -<p class="pcap">Pastel rose quartz has a delicate -beauty in any cut. The 375-carat -step cut (top), the 84-carat step -cut, and the 46-carat marquise -came from Brazil. (Two-thirds -actual size.)</p> -</div> -<div class="img" id="fig51"> -<img src="images/p27a.jpg" alt="" width="800" height="709" /> -<p class="pcap">Amethyst, a purplish quartz, is -the birthstone for February. Here -it is represented by a 1362-carat -stone from Brazil (top), a 54-carat -stone from Pennsylvania (left), -and a 21-carat stone from North -Carolina. (Almost actual size.)</p> -</div> -<p>In addition to possessing wide variation of color, quartz, like -sapphire and certain other gemstones, can exhibit asterism or -chatoyancy. The well-known <i>tiger’s-eye</i> from West Griqualand, -South Africa, owes its eye effect to the fact that its material -is a replacement of fibrous asbestos by cryptocrystalline quartz. -The color of tiger’s-eye arises from the partial alteration of the -asbestos to yellow-brown iron oxides before it is replaced by -quartz. Inclusions of rutile, tourmaline, or actinolite needles -may produce attractive patterns in quartz, but they do not -always cause chatoyancy. The material containing such inclusions -<span class="pb" id="Page_51">51</span> -is called sagenitic quartz, or it may be descriptively -named, such as rutilated quartz, tourmalinated quartz, and so -forth. Sagenitic quartz is usually cut as cabochons rather than -as faceted stones since the inclusions are of greater interest -than the quartz itself.</p> -<p>If the foreign inclusions consist of tiny flakes of hematite or -mica, the quartz assumes a spangled appearance and is called -<i>aventurine</i>.</p> -<p>Crystals of quartz varieties that are opaque or that contain -visible inclusions normally are cut as cabochons to take advantage -of the body color or to make the inclusions more visible. -Crystals of the transparent varieties are fashioned in any of -several cutting styles, depending on whether it is desired to -take maximum advantage of color or of brilliance. Because of -its availability in fairly large, flawless pieces in various colors, -quartz has been used extensively in carving. The Chinese -have excelled in carving large, ornate objects of rock crystal.</p> -<p>Although quartz occurs in many varieties and its crystals are -cut in many styles, it is easily identified by its refractive index -of 1.55, specific gravity of 2.65, and hardness of 7.</p> -<dl class="undent"><dt>CRYSTALLINE VARIETIES</dt> -<dd>Amethyst: Purple to violet</dd> -<dd>Cairngorm: Smoky yellow</dd> -<dd>Citrine: Yellow to red-orange and red-brown</dd> -<dd>Milky quartz: White</dd> -<dd>Morion: Black</dd> -<dd>Rock crystal: Colorless</dd> -<dd>Rose quartz: Rose to pink</dd> -<dd>Smoky quartz: Gray to black</dd></dl> -<dl class="undent"><dt>CRYPTOCRYSTALLINE VARIETIES (CHALCEDONY)</dt> -<dd>Agate: Pronounced color banding</dd> -<dd>Aventurine: Inclusions of sparkling flakes</dd> -<dd>Bloodstone: Dark green dotted with red</dd> -<dd>Carnelian: Red to yellow-red</dd> -<dd>Cat’s-eye: Chatoyant</dd> -<dd>Chrysoprase: Green</dd> -<dd>Jasper: Opaque brown to red-brown, green, yellow, etc.</dd> -<dd>Onyx: Color banding in straight layers of contrasting color</dd> -<dd>Sard: Light to dark brown</dd> -<dd>Sardonyx: Sard or carnelian bands alternating with white bands</dd> -<dd>Tiger’s-eye: Bright brownish yellow, sometimes blue: chatoyant</dd></dl> -<div class="pb" id="Page_52">52</div> -<h3>CHRYSOBERYL -<br /><span class="smaller">(INCLUDES ALEXANDRITE AND CAT’S-EYE)</span></h3> -<p>With color ranging from shades of yellow and brown -through blue-green to olive, and with a hardness of -8½, chrysoberyl has most of the characteristics necessary for a -fine gem. Rare stones of high-quality chrysoberyl demand -fairly high prices, and they are sought eagerly by the connoisseur -of gemstones.</p> -<p>Chrysoberyl is beryllium aluminate, -and thus is closely related to the gemstone -spinel, which is magnesium aluminate. -When pure, chrysoberyl is colorless and -relatively uninteresting as a gemstone -because of its lack of color dispersion and -its moderate refractive index of 1.75. -However, few pure samples are known, as -chrysoberyl normally contains some iron -or chromium in place of aluminum and -some iron in place of beryllium. As a -result of such impurities, the color of -chrysoberyl my be yellowish, greenish, -or brownish.</p> -<p>Chrysoberyl and beryl are the only important -gemstones containing the element -beryllium. The minerals beryllonite, -euclase, hambergite, and phenakite also -contain this element, but they are rare and -seldom are seen as cut gems.</p> -<div class="img" id="fig52"> -<img src="images/p28.jpg" alt="" width="468" height="601" /> -<p class="pcap">One of the finest chrysoberyl cat’s-eyes -in existence is the 58-carat -Maharani from Ceylon. (Actual -size.)</p> -</div> -<p>The <i>alexandrite</i> variety of chrysoberyl has two colors in delicate -balance, and it changes from a columbine red to an -emerald green when viewed under different light. When -viewed in daylight, which is richer in green, the color balance -shifts toward green, and that hue is seen by the observer. Under -artificial light, normally richer in red, the color balance shifts -toward red, and the stone seems to have changed to that color. -<span class="pb" id="Page_53">53</span> -This extremely rare stone, named after Czar Alexander II of -Russia, is found only occasionally, in Russia and Ceylon. The -Russian stones, found with emerald in mica schist, tend to be -smaller than the Ceylon stones and have a color change going -from emerald green to violet-red. The Ceylon stones, found as -pebbles in gem gravels, have a color change going from a less-emerald -green to a browner red. The 66-carat, record-size -alexandrite in the National Collection shows the color change -typical of Ceylon stones. A synthetic stone is commonly -marketed as synthetic alexandrite, but this substitute not only -is man-made but is actually synthetic corundum instead of -synthetic chrysoberyl.</p> -<div class="img" id="fig53"> -<img src="images/p28a.jpg" alt="" width="800" height="516" /> -<p class="pcap">In addition to its fine cat’s-eyes and its color-changing alexandrite -varieties, chrysoberyl occurs in handsome stones that vary in depth -of color. Shown here with an uncut twinned crystal of gem quality -from Brazil are a 46-carat stone from Brazil (left) and a 121-carat -stone from Ceylon. The uncut crystal is a gift of Bernard T. Rocca, Sr. -(Two-thirds actual size.)</p> -</div> -<p><i>Cat’s-eye</i> chrysoberyl contains myriads of tiny fiberlike channels -arranged in parallel position. When the stone is cut as a -cabochon, a band of light is reflected from the curved top of -the stone, producing an effect that resembles the slit pupil of a -cat’s eye.</p> -<dl class="undent"><dt>VARIETIES</dt> -<dd>Alexandrite: Green in daylight, changing to red in artificial light</dd> -<dd>Cat’s-eye: Chatoyant</dd></dl> -<div class="pb" id="Page_54">54</div> -<h3>TOURMALINE</h3> -<p>Because of its great color range, which includes pink, green, -blue, yellow, brown, and black in many different shades -and combinations of shades, tourmaline is one of the most popular -of the colored gemstones. Tourmaline with a color near -emerald green is particularly popular.</p> -<p>Chemically, tourmaline is a very complex borosilicate, and -its color is determined by the various elements present in it. -Tourmaline crystals having sodium, lithium, or potassium are -either colorless, red, or green; those having iron are blue, blue-green, -or black; and those having magnesium are colorless, -yellow-brown, or blackish brown.</p> -<p>Some crystals of tourmaline are of two colors, and stones -of mixed colors, such as pink and green, can be cut from these. -The color mixing may show as zoning with the core color of -the crystal overlaid by another color and perhaps even additional -layers of other colors. Zoned crystals with a core of -deep pink covered by a layer of green have been called “watermelon -tourmaline.” Because its refractive index of about 1.6 is -too low to give it marked brilliance, and its color dispersion -is too low to give it fire, the tourmaline relies almost solely -on the beauty of its color for its rank in popularity.</p> -<p>Although tourmaline has a low refractive index and low dispersion, -it exhibits remarkable dichroism. In other words, it -can present different tints to the viewer depending on the -direction that the light is traveling through the crystal. When -viewed down the long, or vertical, axis of the crystal, the color -of tourmaline is much stronger than when viewed from the side. -This means that if the crystal is dark the cutter will have to cut -the stone with the flat part, or table, parallel to the long axis -of the crystal. The color of the gemstone then will be lightened -when viewed from its table, since this is the direction of -lighter color. Similarly, the table of a lighter colored crystal -can be cut perpendicular to the long axis in order to produce -a deeper colored gem.</p> -<div class="pb" id="Page_55">55</div> -<div class="img" id="fig54"> -<img src="images/p29.jpg" alt="" width="800" height="576" /> -<p class="pcap">Green seems to be the best known commercial color of tourmaline, -but this extremely variable gem species exhibits many subtle shades -of color, as shown here. At upper left, a 104-carat stone from Mozambique; -at upper right, a 173-carat stone from Mozambique; at lower -left, a 111-carat stone from Manchuria; and a 35-carat stone from -Brazil. (Actual size.)</p> -</div> -<p>Some tourmaline crystals contain threadlike tubes or inclusions -of microscopic size running parallel to its length. When -cut as cabochons, such crystals give a good “cat’s-eye” effect.</p> -<p>Tourmaline has no distinct cleavage and has a hardness -somewhat above 7, and these characteristics make the stone -sufficiently resistant to normal shock and wear so that it is -highly satisfactory for use in jewelry.</p> -<p>Noted deposits of tourmaline are located in the Ural -Mountains of Russia, Ceylon, Burma, South-West Africa, -Madagascar, Brazil, Maine, and California. Crystals from each -of these localities seem to have their own color specialties. The -deposits in San Diego County, Calif., are unique in that all -colors except brown are found there. In the early 1900’s -<span class="pb" id="Page_56">56</span> -pink and red tourmaline was shipped from there to China for -carving, but this thriving trade stopped with the end of -Chinese imperial reign. The tourmaline deposits at Paris, -Auburn, and Hebron, Maine, have furnished a number of -excellent gems, especially of blue and green colors.</p> -<dl class="undent"><dt>VARIETIES</dt> -<dd>Achroite: Colorless</dd> -<dd>Indicolite: Blue</dd> -<dd>Dravite: Brown</dd> -<dd>Schorl: Black</dd> -<dd>Rubellite: Pink</dd></dl> -<h3>ZIRCON</h3> -<p>Zircon, because of its high refractive index and high dispersion, -approaches diamond in degree of brilliance and -fire. On only casual examination it is quite possible to mistake -a well-cut, colorless zircon for a diamond. However, a -careful examination of the back facets of such a stone, when -viewed through the table, would show strong double refraction, -a characteristic of zircon but not of diamond. Zircon’s double -refraction makes the back facet edges appear doubled. Since -diamond is “singly refracting,” it cannot produce this double -appearance of the back facets.</p> -<p>Zircon is brittle and has a hardness of just over 7, while -diamond’s hardness, as we have seen, is rated at 10. After -being worn in jewelry for a long period of time, zircon will -show signs of chipping on the facet edges. Under the same -conditions, diamond would remain unchanged. Because of this -tendency for facet edges to chip, it is the practice in the gem -trade to pack cut zircons separately. If a number of zircons -were placed in the same paper packet there would be a risk -of “paper wear.”</p> -<p>In the gem trade, the most important zircons are those that -are colorless, golden brown, or sky blue. Such stones originally -were reddish brown zircon pebbles from Indochina, but they -have been converted by being subjected to temperatures -<span class="pb" id="Page_57">57</span> -approaching 1800° F. for periods of up to two hours. When -the original zircons are heated in a closed container, the stones -become blue or colorless; when a flow of air is allowed through -the container, the stones become golden yellow, red, or -colorless. In most of these converted stones the color remains -quite stable, but in some it may revert to an unattractive -greenish or brownish blue after a period of time.</p> -<div class="img" id="fig55"> -<img src="images/p30.jpg" alt="" width="800" height="677" /> -<p class="pcap">The beautiful colors of these brilliant zircons are the result of heat -treatment given to natural, reddish brown stream pebbles. The three -stones at the left (from top) weigh 118, 103, and 98 carats, and the -ones on the right weigh 106 and 29 carats. The 106-carat stone came -from Thailand, the others from Indochina. (Four-fifths actual size.)</p> -</div> -<p>In addition to being reddish brown, natural zircon may vary -from almost colorless to yellow, red, orange, and brown or -from yellow-green to dark green and, occasionally, blue.</p> -<p>The most important producing areas of gem zircon are in a -region of Indochina that comprises parts of Thailand, Viet Nam, -and Laos. Additional gem zircon, like so many of the other -gem species, is recovered from near Moguk in Upper Burma and -from the gem gravels of Ceylon.</p> -<p>There is no synthetic zircon on the market, but a bright -blue synthetic spinel is sometimes used to simulate zircon -successfully.</p> -<div class="pb" id="Page_58">58</div> -<h3>PERIDOT</h3> -<p>The relative rarity of peridot and the ease with which it -can be simulated in glass, whose luster it approximates, -probably account for the low popular demand for this gemstone. -Although peridot has little brilliance and no fire, its -unusual color and glassy luster produce a unique effect that -serves to make it attractive.</p> -<p>The color of peridot is an unusual bottle green that shades, -in some stones, toward yellow-green and, more rarely, toward -brown. In 1952 it was discovered -that almost all of the brown -gems believed to have been -peridot in various gem collections -were actually of an -entirely unrelated species, which -since has been named sinhalite. -Brown peridot still remains rare -and is somewhat of a collector’s -item.</p> -<div class="img" id="fig56"> -<img src="images/p31.jpg" alt="" width="382" height="800" /> -<p class="pcap">To exhibit its unique color to best -advantage, peridot usually is cut -so as to have a relatively large -table, as shown in these examples. -The largest gem, weighing 310 -carats, is from the Egyptian island -of Zebirget in the Red Sea and is -the largest cut peridot known. The -other two, weighing 287 carats -and 109 carats, are from Burma. -(Three-fifths actual size.)</p> -</div> -<p>The green of peridot, which -is quite different from the green -of other gemstones, is due to -some iron included in its composition. -It is suspected that a -<span class="pb" id="Page_59">59</span> -trace of nickel contributes to the liveliness of the color.</p> -<div class="img" id="fig57"> -<img src="images/p31a.jpg" alt="" width="800" height="531" /> -<p class="pcap">This photo shows the color of peridot projected onto the background. -The larger gem is the 310-carat stone shown in the prior illustration. -The stone on the right weighs 109 carats and is -from Burma; the other peridot weighs 46 carats and is from Egypt. -(Almost actual size.)</p> -</div> -<p>Peridot has a hardness of only 6½ and a rather strong -tendency to cleave, and these characteristics reduce its value -for use in jewelry exposed to rough wear. It is better used in -pins, earrings, and pendants than in rings.</p> -<p>Peridot is a gem name for the common mineral olivine, a -magnesium silicate. Olivine is fund in numerous places, and -small gemmy pieces are found in many localities. Many of the -largest and best gems of peridot have come from mines on the -Egyptian island of Zebirget (Island of St. John) in the Red -Sea, but most gem peridot now comes from Burma. Great numbers -of small stones have been cut from olivine found in Arizona -gravels.</p> -<p>Centuries ago, peridot was known by the name topaz, since -the stones came from Topazos, the island now known as -Zebirget. The name topaz, as we have seen, is used today for an -entirely different mineral species.</p> -<div class="pb" id="Page_60">60</div> -<h3>SPODUMENE</h3> -<p>Spodumene, a lithium aluminum silicate, is one of the very -few gemstones containing lithium. It has had more importance -as a gemstone in the United States than elsewhere, a -situation due to early discoveries of unique occurrences of a -lavender-pink variety at Branchville, Conn., in 1879 and in -San Diego County, Calif, about 20 years later. At the time of -the discovery of the California material, the variety was -named <i>kunzite</i> in honor of G. F. Kunz, a noted American -gemologist of the times.</p> -<div class="img" id="fig58"> -<img src="images/p32.jpg" alt="" width="800" height="637" /> -<p class="pcap">The 177-carat kunzite (at lower left) is a large flawless stone cut -from California material of this variety of spodumene. It was given -to the Smithsonian Institution by the American Gem Society. The -other stones, all from Brazil, represent the more usual shades of -spodumene. They weigh 327 carats (top left), 256 carats (top right), -and 69 carats. (About half actual size.)</p> -</div> -<p>The finding of a bright green variety, <i>hiddenite</i>, in North -Carolina about 1880 greatly stimulated the interest of American -gem collectors. Some of the bright green spodumene -<span class="pb" id="Page_61">61</span> -coming from Brazil in recent years compares very favorably in -color with North Carolina hiddenite. Other than in a scattered -few of these unusual occurrences of kunzite and hiddenite, -spodumene usually is found in yellow and yellow-green -shades, with Brazil and Madagascar being the chief sources.</p> -<div class="img" id="fig59"> -<img src="images/p32a.jpg" alt="" width="800" height="688" /> -<p class="pcap">This 880-carat kunzite from Brazil is one of the largest stones of its -kind. (About actual size.)</p> -</div> -<p>Spodumene has a hardness of about 7, but with a refractive -index of about 1.66 and a low dispersion there seems to be -relatively little to recommend it as a gemstone. The fact that it -exhibits a very strong tendency to cleave in two different -directions would seem to rule it out completely as being too -difficult to cut. Nevertheless, the production and purchase of -cut stones of spodumene persist because of the beauty of -the gem.</p> -<p>The kunzite and hiddenite varieties of spodumene show -strong <i>pleochroism</i>, or the ability to show three different colors -when viewed in the direction of different axes. Some of the -large Brazilian kunzite crystals mined in the early 1960’s have -<span class="pb" id="Page_62">62</span> -an intense rose-violet color when viewed along the long axis -of the crystal but have pale blue-violet and pale tan colors -when viewed from the other two directions. When heat -treated, or exposed to strong light, this Brazilian kunzite -loses its tan and bluish colors but retains the intense rose-violet. -Because of spodumene’s pleochroism, the direction of -cutting in the stones becomes extremely important, as it -must be done in a manner that will take advantage of the -violet color in kunzite and the green color in hiddenite.</p> -<dl class="undent"><dt>VARIETIES</dt> -<dd>Kunzite: Lavender violet to rose violet</dd> -<dd>Hiddenite: Deep green</dd></dl> -<h3>GARNET</h3> -<p>The name garnet is applied to a group of six closely related -silicate minerals that are alike in crystal structure but -that differ mainly in the substitution of certain metallic -elements in their composition. These minerals are:</p> -<dl class="undent"><dt><i>Pyrope</i>, magnesium aluminum garnet</dt> -<dt><i>Almandine</i>, iron aluminum garnet</dt> -<dt><i>Spessartine</i>, manganese aluminum garnet</dt> -<dt><i>Uvarovite</i>, calcium chromium garnet</dt> -<dt><i>Grossular</i>, calcium aluminum garnet</dt> -<dt><i>Andradite</i>, calcium iron garnet</dt></dl> -<p>Most natural garnets have compositions intermediate between -members of the basic group of six. For example, there are -garnets having compositions anywhere between pyrope and -almandine, depending on the amount of difference in the -magnesium or iron content. These same garnets may even have -varying amounts of manganese, and thus be partially -spessartine.</p> -<p>The six garnets in the basic group are found in considerable -quantity in many areas, but seldom are they of sufficiently high -quality to be considered gemstone material. Even when stones -of gem quality are found, their colors—particularly the reds—tend -to be so intense that they seem to be opaque.</p> -<div class="pb" id="Page_63">63</div> -<div class="img" id="fig60"> -<img src="images/p33.jpg" alt="" width="800" height="616" /> -<p class="pcap">Garnets occur in several colors, although most people think of them -as red. Shown here are a 54-carat spessartine from Brazil (top -right), a 6-carat rhodolite from North Carolina (at left), a magnificent -10-carat green demantoid from Russia, a 9-carat grossular from -Ceylon (bottom), and a 26-carat spessartine from Virginia. (Seven-eighths -actual size.)</p> -</div> -<p>Garnet has a hardness (about 7) suitable for gemstone -material and a fairly high refractive index (1.74 and above).</p> -<p>Ruby red pyrope is the most popular variety of garnet. It is -found in Bohemia, in Czechoslovakia, where it occurs as small, -poorly shaped crystals. Red pyrope also is found in Africa, -where it is called Cape ruby, and in Arizona, where it is sold -as Arizona ruby. Another kind of pyrope called <i>rhodolite</i> is noted -for its soft, rosy purple color. Actually, rhodolite is one of the -intermixed garnets with a composition somewhere between -pyrope and almandine. Most of the fine rhodolite gems have -come from North Carolina.</p> -<p>Almandine is popular in its deep red, transparent form, but -since the red is so dark and intense that it appears black, the -stones usually are cut as cabochons with the back hollowed -out. This makes them thinner, and thus lightens their color. -Garnets cut in this manner are all known as carbuncles. -<span class="pb" id="Page_64">64</span> -Brazil, India, Ceylon, Australia, and parts of the United -States are important sources of almandine.</p> -<p>Although spessartine has a rich orange color, it is not often -used as a gemstone because of the relative rarity of gem-quality -cutting material. This mineral gets its name from the -town of Spessart, Germany, where it was first found. Excellent -spessartine with colors ranging from orange to brown has -been found at Amelia Court House, Va., and quality gems -have been cut from such material. Ceylon, Burma, Madagascar, -and Brazil also have furnished some gem spessartine.</p> -<p>The chromium garnet, uvarovite, generally is too poor in -quality for cutting. Uvarovite crystals, which are emerald -green in color, occur in only small sizes. They are found -mostly in Russia, Finland, and California.</p> -<p>Grossular varies in color. It occurs chiefly in some shade of -red, green, yellow, or brown, depending on the impurities -present. When pure, grossular is colorless. A kind of grossular -called <i>hessonite</i> has an attractive cinnamon color, and it is found -mainly in Ceylon. Because of its color it can easily be confused -with spessartine, which it closely resembles.</p> -<p>Andradite, a very common garnet, usually is found in -shades of red, black, brown, yellow, or green. Some types of -gem andradite have special names for different colors: <i>topazolite</i>, -yellow; <i>demantoid</i>, green; and <i>melanite</i>, sparkling black. The -very valuable demantoid is found in Russia and Italy.</p> -<dl class="undent"><dt>VARIETIES:</dt> -<dd>Grossular: Colorless, green, amber, brownish yellow, rose</dd> -<dd class="t">Hessonite: Cinnamon colored</dd> -<dd>Pyrope: Deep red</dd> -<dd class="t">Rhodolite: Rose red and purple</dd> -<dd>Almandine: Deep red</dd> -<dd>Spessartine: Brownish red to orange</dd> -<dd>Andradite: Yellow, greenish yellow, emerald green, brownish red, brownish yellow, brown, black</dd> -<dd class="t">Topazolite: Yellow to greenish</dd> -<dd class="t">Demantoid: Grass green to emerald green</dd> -<dd class="t">Melanite: Black</dd> -<dd>Uvarovite: Green</dd></dl> -<div class="pb" id="Page_65">65</div> -<h3>JADE</h3> -<p>The name jade is applied to two unrelated minerals—<i>nephrite</i> -and <i>jadeite</i>—that have somewhat similar characteristics.</p> -<p>Jadeite, the rarer of the two, is a sodium aluminum silicate -that belongs to a group of rock-forming minerals known as -pyroxenes. Its color varies from white to emerald green and -many other colors. Jadeite is highly prized, and when it occurs -as emerald green it is considered one of the most valuable -gemstones. This -kind of jade is -found in many -places, but the most -important occurrence -is in Upper -Burma. Nephrite, a -more common species, -is a calcium -magnesium iron silicate -belonging to a -group of rock-forming -minerals known -as amphiboles. The -color varies from white to a dark spinach green and black. -Among the places where nephrite occurs are New Zealand, -Turkestan, Siberia, Alaska, China, Silesia, and certain parts -of the western United States, notably in Wyoming and -California.</p> -<div class="img" id="fig61"> -<img src="images/p34.jpg" alt="" width="699" height="799" /> -<p class="pcap">This emerald green jadeite carving, -dating from the Ch’ien-lung -period (1736-1795), stands -6½ inches without the base. -It was given to the Smithsonian -as part of the Maude -Monell Vetlesen collection.</p> -</div> -<div class="pb" id="Page_66">66</div> -<p>Jade is not particularly hard (6½), but it is very tough, and -this characteristic makes it an excellent material for carving. -Even when subjected to punishing usage, jade resists chipping -and wear. It was used for making tools and weapons by -primitive peoples who lived in what is now Mexico, Switzerland, -France, Greece, Egypt, Asia Minor, and in other places. -The jade implements fashioned by these peoples have survived -well the ravages of time.</p> -<p>The Chinese and Japanese prize jade highly. In their -countries, tradition has assigned to jade medicinal and spiritual -values, and has associated with it the cardinal virtues of -charity, modesty, courage, justice, and wisdom. As a consequence, -these peoples long ago developed the carving of jade -as a high art. Among the -magnificent Chinese jade -carvings in the National Gem -Collection are 130 pieces -produced mostly during the -Ching Dynasty (1644-1912), -when the art of jade carving -was at its peak. Many of these -jades were carved in imitation -of the revered bronze -ceremonial vessels of ancient -times. This collection was -presented to the Smithsonian -Institution in 1959 by Mr. -Edmund C. Monell in behalf -of the estate of his mother, -Mrs. Maude Monell Vetlesen -of New York.</p> -<div class="img" id="fig62"> -<img src="images/p35.jpg" alt="" width="466" height="800" /> -<p class="pcap">This pale green jade vase of the -Ch’ien-lung period is 14½ inches high -without the base. It is one of a matched -pair presented as part of the Maude -Monell Vetlesen collection of carved -jade.</p> -</div> -<div class="pb" id="Page_67">67</div> -<h3>CHARACTERISTICS OF SOME COMMON GEMS</h3> -<table class="center"> -<tr class="th"><th> </th><th class="l" colspan="4">Approximate average of</th></tr> -<tr class="th"><th> </th><th class="l" colspan="4">(1) hardness</th></tr> -<tr class="th"><th> </th><th class="l" colspan="4">(2) specific gravity </th><th class="l" colspan="2">(4) Dispersion</th></tr> -<tr class="th"><th> </th><th class="l" colspan="4">(3) refractive index </th><th class="l" colspan="2">(5) Durability</th></tr> -<tr class="th"><th>Species </th><th>(1) </th><th>(2) </th><th>(3) </th><th>(4) </th><th>(5) </th><th>Usual color range</th></tr> -<tr><td class="l">Beryl </td><td class="l">7¾ </td><td class="l">2.70 </td><td class="l">1.58 </td><td class="l">Low </td><td class="l">High </td><td class="l">Green (emerald), blue-green (aquamarine), pink (morganite), colorless (goshenite)</td></tr> -<tr><td class="l">Chrysoberyl </td><td class="l">8½ </td><td class="l">3.71 </td><td class="l">1.75 </td><td class="l">Low </td><td class="l">High </td><td class="l">Yellow, green, brown</td></tr> -<tr><td class="l">Corundum </td><td class="l">9 </td><td class="l">4.00 </td><td class="l">1.77 </td><td class="l">Low </td><td class="l">High </td><td class="l">Red (ruby), various (sapphire)</td></tr> -<tr><td class="l">Diamond </td><td class="l">10 </td><td class="l">3.52 </td><td class="l">2.42 </td><td class="l">High </td><td class="l">High </td><td class="l">Colorless</td></tr> -<tr><td class="l">Garnet group </td><td class="l">7½ </td><td class="l">3.70-4.16 </td><td class="l">1.74-1.89 </td><td class="l">Medium<br />to high </td><td class="l">High </td><td class="l">Yellow, red, green, brown</td></tr> -<tr><td class="l">Jade (nephrite) </td><td class="l">6½ </td><td class="l">2.96 </td><td class="l">1.62 </td><td class="l">None </td><td class="l">High </td><td class="l">Green, white</td></tr> -<tr><td class="l">Jade (jadeite) </td><td class="l">7 </td><td class="l">3.33 </td><td class="l">1.66 </td><td class="l">None </td><td class="l">High </td><td class="l">Green, white</td></tr> -<tr><td class="l">Opal </td><td class="l">6 </td><td class="l">2.10 </td><td class="l">1.45 </td><td class="l">None </td><td class="l">Low </td><td class="l">Red, dark gray, orange, white, with or without varicolored fire</td></tr> -<tr><td class="l">Pearl </td><td class="l">3½ </td><td class="l">2.71 </td><td class="l">None </td><td class="l">None </td><td class="l">Low </td><td class="l">White</td></tr> -<tr><td class="l">Peridot </td><td class="l">6½ </td><td class="l">3.34 </td><td class="l">1.68 </td><td class="l">Low </td><td class="l">Medium </td><td class="l">Yellow-green, brownish green</td></tr> -<tr><td class="l">Quartz </td><td class="l">7 </td><td class="l">2.65 </td><td class="l">1.55 </td><td class="l">Low </td><td class="l">High </td><td class="l">Purple (amethyst), yellow (citrine), colorless (rock crystal)</td></tr> -<tr><td class="l">Spinel </td><td class="l">8 </td><td class="l">3.60 </td><td class="l">1.72 </td><td class="l">Low </td><td class="l">High </td><td class="l">Shades of red, green, blue, violet</td></tr> -<tr><td class="l">Spodumene </td><td class="l">7 </td><td class="l">3.18 </td><td class="l">1.66 </td><td class="l">Low </td><td class="l">Low </td><td class="l">Colorless, pink, yellow, green</td></tr> -<tr><td class="l">Topaz </td><td class="l">8 </td><td class="l">3.54 </td><td class="l">1.63 </td><td class="l">Low </td><td class="l">Medium </td><td class="l">Colorless, sherry, pink, blue</td></tr> -<tr><td class="l">Tourmaline </td><td class="l">7 </td><td class="l">3.06 </td><td class="l">1.63 </td><td class="l">Low </td><td class="l">High </td><td class="l">Wide range, except bright red</td></tr> -<tr><td class="l">Zircon </td><td class="l">7 </td><td class="l">4.02 </td><td class="l">1.81 </td><td class="l">High </td><td class="l">High </td><td class="l">Almost colorless, blue, brown, green, yellow</td></tr> -</table> -<div class="pb" id="Page_68">68</div> -<h3>GEMSTONES FOR THE COLLECTOR</h3> -<p>A number of mineral species have produced cut gemstones -that fulfill every necessary requirement of beauty, -durability, and rarity, but their popularity and commercial -success have been sharply limited because of insufficient supply. -In some cases of even adequate supply such gemstones do not -compete with other, more plentiful kinds that exhibit the same -characteristics. The scarcity of these minerals does not diminish -their standing as potential gem material—it merely points up -the effect of accidental natural distribution of these species.</p> -<div class="img" id="fig63"> -<img src="images/p36.jpg" alt="" width="800" height="604" /> -<p class="pcap">A magnificent set of 16 -matched sphenes from -Switzerland, gift of Nina -Lea, almost encircles a -110-carat sinhalite (a rare -magnesium borate) and -a 22-carat kornerupine, -both from Ceylon. The -man’s gold ring indicates -the sizes of these unusual -stones.</p> -</div> -<p>Among the rarer minerals that produce good gemstones are -cordierite, benitoite, euclase, phenakite, beryllonite, willemite, -wernerite, danburite, datolite, axinite, brazilianite, andalusite, -sillimanite, kyanite, kornerupine, enstatite, diopside, epidote, -sphene, sinhalite, and orthoclase. Willemite, a rare zinc silicate -found in only a few localities, is typical of these rarer minerals. -The famous zinc mines at Franklin, N. J., produced a few large -gemmy crystals of willemite, and some fine gemstones were cut -<span class="pb" id="Page_69">69</span> -from some of these. Willemite’s borderline hardness of 5 to 5½ -and its extreme rarity effectively eliminate it from the gem -market, but the collector who is able to obtain a good stone of -this material is indeed fortunate.</p> -<div class="img" id="fig64"> -<img src="images/p36a.jpg" alt="" width="800" height="582" /> -<p class="pcap">Exotic gems that represent collectors’ items lie beside a 3¼-inch-long -box of Russian lapis lazuli. The stones are (left row, from top) -a 28-carat andalusite from Brazil, gift of Fred C. Kennedy, a 10-carat -cordierite from Ceylon, a 29-carat apatite from Burma, and (right -row) a 42-carat brazilianite from Brazil, a 13-carat euclase from -Brazil, a 29-carat wernerite from Brazil, and a 61-carat orthoclase -from Madagascar.</p> -</div> -<p>Some mineral species, although beautiful when cut, and -prized by collectors, are entirely too soft, are too easily -cleaved, or have some other physical weakness that renders them -useless as commercial gemstones. Sphalerite, apatite, fluorite, -calcite, cerussite, zincite, and hematite are included in this -group. Sphalerite is typical; it produces brilliant and colorful -gemstones that hold their own among other stones of great -beauty. Unfortunately, this zinc sulfide, with a hardness of -3½ to 4, is so soft and cleaves so readily that it is very -difficult to cut properly, and it cannot be used in jewelry.</p> -<div class="pb" id="Page_70">70</div> -<h2 id="c7"><span class="small">7</span> -<br />SOME NOTABLE GEMS IN THE COLLECTION</h2> -<p>The Smithsonian’s collection of gems continues to grow and improve -rapidly, and it changes character constantly as important new -gemstones are added and less important ones are retired. Approximately -one-third of the gems in the collection in 1965 are itemized in the -following list. Included are some of the largest gems of each kind, some -of the more interesting stones, and some small gems notable for the -places from which they came. Though listed by species and size, some -of the larger stones are not included, and neither are most cabochons, -rough opal, beads, carvings, and spheres. The descriptions listed include, -in order, weight in carats; color; popular name or other description, if -any; place of origin; and U. S. National Museum catalog number and -name of donor. Gems in the Lea and Roebling collections usually are -indicated by the letters “L” and “R.”</p> -<dl class="undent"><dt class="center">DIAMOND</dt> -<dt>127, colorless (<i>The Portuguese</i>), Brazil (3398)</dt> -<dt>44.5, blue (<i>The Hope</i>), India (3551, Winston)</dt> -<dt>18.3, yellow (<i>The Shephard</i>), South Africa (3406)</dt> -<dt>2.9, pink, Tanzania (3772, De Young)</dt> -<dt class="center">CORUNDUM: <span class="sc">Ruby</span></dt> -<dt>50, red-violet (a star), Ceylon (173, L)</dt> -<dt>34, red (a star), Ceylon (1922, L)</dt> -<dt class="center">CORUNDUM: <span class="sc">Sapphire</span></dt> -<dt>330, blue (<i>Star of Asia</i>), Burma (3688)</dt> -<dt>316, blue (<i>Star of Artaban</i>), Ceylon (2231, Ingram)</dt> -<dt>93, yellow, Burma (3549)</dt> -<dt>52, yellow, Burma (3419)</dt> -<dt>40, blue (a star), Ceylon (174, L)</dt> -<dt>35, yellow-brown, Ceylon (2147, L)</dt> -<dt>26, gray (a star), Ceylon (3902)</dt> -<dt>26, colorless, Ceylon (2016, L)</dt> -<dt>25, blue (4-starred), Ceylon (3923, Krandall)</dt> -<dt>22, yellow-orange, Ceylon (3875, L)</dt> -<dt>16, colorless, Ceylon (3581, L)</dt> -<dt class="center">BERYL: <span class="sc">Emerald</span></dt> -<dt>157, green, India (3601)</dt> -<dt>117, green, Colombia (4158, Erickson)</dt> -<dt>27, green, Colombia (3922)</dt> -<dt>17, green (3920, MacVeagh)</dt> -<dt>7, green, North Carolina (3075, L)</dt> -<dt>4.6, green (a cat’s-eye), Colombia (2256, R)</dt> -<dt class="pb" id="Page_71">71</dt> -<dt class="center">BERYL: <span class="sc">Aquamarine</span></dt> -<dt>1000, green, Brazil (3889, Evyan)</dt> -<dt>264, blue, Russia (3606, Neal)</dt> -<dt>187, blue, Brazil (3683)</dt> -<dt>126, blue, Brazil (4159, Erickson)</dt> -<dt>71, pale blue, Ceylon (3172, L)</dt> -<dt>66, pale blue-green, Maine (2148, L)</dt> -<dt>15, blue-green, Idaho (2249, Montgomery)</dt> -<dt>14, blue, Connecticut (779)</dt> -<dt>10, blue, North Carolina (776, L)</dt> -<dt class="center">BERYL: <span class="sc">Morganite</span></dt> -<dt>236, pink, Brazil (3780, Ix)</dt> -<dt>122, pale pink, California (1988, R)</dt> -<dt>80, pale pink, Brazil (4190, R)</dt> -<dt>64, pink, Brazil (3721, R)</dt> -<dt>56, pink, Madagascar (2223, R)</dt> -<dt>51, pink, Brazil (3623)</dt> -<dt class="center">BERYL: <span class="sc">Beryl</span></dt> -<dt>2054, green-gold, Brazil (3725, R)</dt> -<dt>1363, green, Brazil (3916)</dt> -<dt>914, green, Brazil (3919)</dt> -<dt>578, green, Brazil (3227, R)</dt> -<dt>133, yellow, Madagascar (1977, L)</dt> -<dt>114, yellow-green, Brazil (2245, R)</dt> -<dt>98, pale green, Brazil (3949, Cutter)</dt> -<dt>62, colorless (goshenite), Brazil (3366)</dt> -<dt>46, gold, Madagascar (2121, L)</dt> -<dt>44, gold (a cat’s-eye), Madagascar (3248)</dt> -<dt>40, pale green, Connecticut (1037, L)</dt> -<dt>40, yellow-green, North Carolina (2260, Roebling)</dt> -<dt>20, brown (a star), Brazil (3355, L)</dt> -<dt class="center">TOPAZ</dt> -<dt>7725, yellow, Brazil (3976)</dt> -<dt>3273, blue, Brazil (3633)</dt> -<dt>1469, yellow-green, Brazil (3891)</dt> -<dt>685, pale blue, Brazil (3003)</dt> -<dt>398, pale blue, Russia (3400, R)</dt> -<dt>235, colorless, Colorado (3309, L)</dt> -<dt>187, colorless, Brazil (3612, Cutter)</dt> -<dt>171, champagne, Madagascar (3890)</dt> -<dt>155, blue, Russia (262, L)</dt> -<dt>146, pale blue, Texas (3625, L)</dt> -<dt>129, sherry, Brazil (3550)</dt> -<dt>94, orange, Brazil (3401, R)</dt> -<dt>54, blue, Brazil (2219, L)</dt> -<dt>51, colorless, Japan (268)</dt> -<dt>44, blue, Maine (2047, L)</dt> -<dt>41, orange, Brazil (2174, L)</dt> -<dt>34, gold, Brazil (2046, L)</dt> -<dt>34, deep pink, Brazil (2232, L)</dt> -<dt>24, pale blue, New Hampshire (3307, L)</dt> -<dt>18, rose pink, Brazil (3402, R)</dt> -<dt>17, blue, California (3679, Ware)</dt> -<dt>15, sherry, Colorado (318, L)</dt> -<dt class="center">TOURMALINE: <span class="sc">Rubellite</span></dt> -<dt>111, pink, Manchuria (3173, R)</dt> -<dt>62, pink, Brazil (3411, R)</dt> -<dt>51, magenta, Brazil (4160, Erickson)</dt> -<dt>35, pink, Brazil (2254, R)</dt> -<dt>34, pink, Brazil (3148, R)</dt> -<dt>30, pink, Madagascar (3409, R)</dt> -<dt>18, pink (a cat’s-eye), California (3786, Lea)</dt> -<dt>18, pink, Maine (1109, L)</dt> -<dt>15, pink, California (3412, R)</dt> -<dt class="center">TOURMALINE: <span class="sc">Tourmaline</span></dt> -<dt>173, champagne, Mozambique (3590, R)</dt> -<dt>125, champagne, Mozambique (3576, R)</dt> -<dt>123, green, Mozambique (3575, R)</dt> -<dt>110, green, Brazil (4197)</dt> -<dt>104, rose, Mozambique (3256, L)</dt> -<dt>76, dark green (a cat’s-eye), Brazil (3599, L)</dt> -<dt>60, blue-green, Brazil (3410, R)</dt> -<dt>58, green, Maine, (1108, L)</dt> -<dt>53, green (a cat’s-eye), Brazil (3119, L)</dt> -<dt>48, red and green, California (3363)</dt> -<dt>42, yellow, Brazil (2251, R)</dt> -<dt>42, brown, Ceylon (3245, L)</dt> -<dt>40, red-brown, Brazil (2097, R)</dt> -<dt>40, green, Madagascar (4081, R)</dt> -<dt>34, red-brown, Brazil (2253, L)</dt> -<dt>31, rose-brown, Brazil (3416, R)</dt> -<dt>26, blue (indicolite), Brazil (3298, R)</dt> -<dt>20, blue-green, Madagascar (2032, L)</dt> -<dt>18, yellow-green, Elba (3368, R)</dt> -<dt>18, green, South Africa (2095, L)</dt> -<dt>15, yellow, Brazil (3415, R)</dt> -<dt class="pb" id="Page_72">72</dt> -<dt class="center">SPINEL</dt> -<dt>46, pale purple, Ceylon (2180, L)</dt> -<dt>36, indigo, Burma (3685)</dt> -<dt>34, red, Burma (3354, L)</dt> -<dt>30, pink-violet, Ceylon (2165, L)</dt> -<dt>30, violet, Burma (3344, L)</dt> -<dt>26, blue-gray, Burma (3593, L)</dt> -<dt>22, blue-violet, Ceylon (2247, R)</dt> -<dt>22, rose-brown, Ceylon (2166, L)</dt> -<dt class="center">ZIRCON</dt> -<dt>118, brown, Ceylon (2236, R)</dt> -<dt>106, brown, Thailand (3568)</dt> -<dt>103, blue, Indochina (2222, R)</dt> -<dt>98, yellow-brown, Ceylon (2237, R)</dt> -<dt>76, red-brown, Burma (3068, L)</dt> -<dt>64, brown, Indochina (3397, R)</dt> -<dt>48, colorless, Ceylon (3554, L)</dt> -<dt>29, blue, Indochina (3394, R)</dt> -<dt>23, green, Ceylon (2233, R)</dt> -<dt>21, tan, Australia (1887, L)</dt> -<dt class="center">SPODUMENE: <span class="sc">Kunzite</span></dt> -<dt>830, deep violet, Brazil (3940)</dt> -<dt>336, deep violet, Brazil (3942, Nelson)</dt> -<dt>297, deep violet, Brazil (3941, Nelson)</dt> -<dt>177, violet, California (3797, American Gem Society)</dt> -<dt>25, pale violet, Madagascar (1979, L)</dt> -<dt class="center">SPODUMENE: <span class="sc">Spodumene</span></dt> -<dt>327, yellow, Brazil (3396, R)</dt> -<dt>256, yellow, Brazil (3429, R)</dt> -<dt>71, yellow, Madagascar (3698, L)</dt> -<dt>69, yellow-green, Brazil (3885, R)</dt> -<dt class="center">PERIDOT</dt> -<dt>310, olive green, Egypt (3398, R)</dt> -<dt>287, olive green, Burma (3705)</dt> -<dt>46, olive green, Egypt (1978, L)</dt> -<dt>23, olive green, Arizona (3620, L)</dt> -<dt class="center">GARNET: <span class="sc">Almandine</span></dt> -<dt>175, red (a star), Idaho (3670)</dt> -<dt>67, red-brown (a star), Idaho (3560, L)</dt> -<dt>41, red-brown, Madagascar (2137, L)</dt> -<dt>26, red-brown, Idaho (3423, L)</dt> -<dt class="center">GARNET: <span class="sc">Demantoid</span></dt> -<dt>10.4 green, Russia (2175)</dt> -<dt class="center">GARNET: <span class="sc">Grossular</span></dt> -<dt>64, orange-brown, Ceylon (493, L)</dt> -<dt class="center">GARNET: <span class="sc">Rhodolite</span></dt> -<dt>25, rose-violet, Tanzania (4080, L)</dt> -<dt>6.4, violet, North Carolina (460, L)</dt> -<dt class="center">GARNET: <span class="sc">Spessartine</span></dt> -<dt>109, red, Brazil (4203)</dt> -<dt>40, orange, Virginia (147, L)</dt> -<dt>26, orange, Virginia (3597, L)</dt> -<dt class="center">QUARTZ: <span class="sc">Amethyst</span></dt> -<dt>1362, purple, Brazil (3879)</dt> -<dt>183, purple, Brazil (1272, L)</dt> -<dt>62, purple, Brazil (3162, Capps)</dt> -<dt>61, purple, Brazil (3914, Cutter)</dt> -<dt>56, purple, Brazil (3165, Capps)</dt> -<dt>54, purple, Pennsylvania (1299, L)</dt> -<dt>45, pale purple, North Carolina (1298, Lea)</dt> -<dt>36, purple, Pennsylvania (1283, L)</dt> -<dt>33, pale purple, North Carolina (1288, Lea)</dt> -<dt>27, purple, Arizona (3291, R)</dt> -<dt>23, purple, Maine (1271, L)</dt> -<dt>19, purple, Virginia (1301, L)</dt> -<dt class="center">QUARTZ: <span class="sc">Citrine</span></dt> -<dt>1180, golden brown, Brazil (1870, L)</dt> -<dt>783, light golden brown, Brazil (3640)</dt> -<dt>278, golden brown, Brazil (3732, Cutter)</dt> -<dt>265, light golden brown, Brazil (2041, Roebling)</dt> -<dt>218, golden brown, Brazil (4199, Cutter)</dt> -<dt>169, golden brown, Australia (1373, L)</dt> -<dt>143, yellow, Colorado (456, L)</dt> -<dt>120, golden brown, Brazil (2116, L)</dt> -<dt>115, golden brown, Brazil (3932)</dt> -<dt>91, yellow, Brazil (3615, Cutter)</dt> -<dt>55, light golden brown, Maine (2178, L)</dt> -<dt>48, yellow, Brazil (3915, Cutter)</dt> -<dt>43, yellow, Brazil (3719, Cutter)</dt> -<dt class="center">QUARTZ: <span class="sc">Rock Crystal</span></dt> -<dt>7000, colorless, Brazil (3957, R)</dt> -<dt>625, colorless (a star), New Hampshire (3125, Burroughs)</dt> -<dt>350, colorless, North Carolina (1398, L)</dt> -<dt class="pb" id="Page_73">73</dt> -<dt class="center">QUARTZ: <span class="sc">Rose Quartz</span></dt> -<dt>375, pink, Brazil (3592, L)</dt> -<dt>84, pink, Brazil (3421)</dt> -<dt>49, pink, Brazil (3420, R)</dt> -<dt class="center">QUARTZ: <span class="sc">Smoky Quartz</span></dt> -<dt>4500, pale smoky, California (3738, L)</dt> -<dt>1695 smoky, Brazil (3697, L)</dt> -<dt>785, pale smoky, Colorado (1335, L)</dt> -<dt>284, pale smoky, North Carolina (1340, Lea)</dt> -<dt>163, pale smoky, Colorado (1336, L)</dt> -<dt>145, smoky, Scotland (3079, R)</dt> -<dt class="center">CHRYSOBERYL: <span class="sc">Alexandrite</span></dt> -<dt>66, green to red, Ceylon (2042, L)</dt> -<dt>17, green to red, Ceylon (3407, R)</dt> -<dt>11, green to red, Ceylon (2200, Walcott)</dt> -<dt class="center">CHRYSOBERYL: <span class="sc">Chrysoberyl</span></dt> -<dt>172, gray-green (a cat’s-eye), Ceylon (3924)</dt> -<dt>121, green (<i>The Maharani</i>, a cat’s-eye), Ceylon (3642)</dt> -<dt>46, green-yellow, Brazil (1923, L)</dt> -<dt>32, brown, Ceylon (2151, L)</dt> -<dt class="center">OPAL</dt> -<dt>155, white with fire, Australia (3285, Roebling)</dt> -<dt>83, white with fire, Australia (3300, R)</dt> -<dt>58, black with fire, Australia (3960, R)</dt> -<dt>56, colorless with fire, Mexico (2240, R)</dt> -<dt>54, black with fire, Australia (3962)</dt> -<dt>44, black with fire, Australia (3284, R)</dt> -<dt>39, pale yellow-orange with fire, Brazil (3637)</dt> -<dt>38, black with fire, Australia (3961)</dt> -<dt>30, black with fire, Australia (3405, R)</dt> -<dt>24, black with fire, Australia (1897, L)</dt> -<dt>22, orange with fire, Mexico (2106, L)</dt> -<dt>22, orange with fire, Mexico (2028, L)</dt> -<dt>21, yellow with fire, Mexico (2111, L)</dt> -<dt>15, orange with fire, Mexico (2096, L)</dt> -<dt>11, orange with fire, Mexico (3886, Lewis)</dt> -<dt class="center">OTHER, LESS-KNOWN SPECIES</dt> -<dt>Albite: 43, white (a cat’s-eye), Burma (3311, L)</dt> -<dt>Amblygonite: 63, yellow, Brazil (4079, Lea)</dt> -<dd>20, yellow, Burma (3562, R)</dd> -<dt>Andalusite: 28, brown, Brazil (3619, Kennedy)</dt> -<dd>14, green-brown, Brazil (3364, L)</dd> -<dt>Apatite: 29, yellow-green, Burma (3247, Lea)</dt> -<dd>29, yellow, Mexico (3594, L)</dd> -<dd>15, colorless, Burma (3720, R)</dd> -<dd>9, yellow-green, Canada (3122, R)</dd> -<dd>8.8, pale blue, Ceylon (3639)</dd> -<dd>5.4, green, Madagascar (3676, Durand)</dd> -<dt>Axinite: 9.4, brown, Mexico (3787, R)</dt> -<dd>9, brown, Mexico (3773, L)</dd> -<dt>Barite: 61, colorless, England (3349)</dt> -<dt>Benitoite: 7.6, blue, California (3387, R)</dt> -<dt>Beryllonite: 5, colorless, Maine (423)</dt> -<dt>Brazilianite: 42, yellow, Brazil (3083, L)</dt> -<dt>Calcite: 46, gold-brown, Mexico (3305)</dt> -<dt>Cassiterite: 10, yellow-brown, Bolivia (3250)</dt> -<dt>Cobaltocalcite: 3.3, 3.9, pink, Spain (3724, L)</dt> -<dt>Cordierite: 16, blue, Ceylon (3882)</dt> -<dd>10, indigo, Ceylon (3580, L)</dd> -<dd>9.4, blue, Ceylon (3881)</dd> -<dt>Danburite: 18, yellow, Burma (3345, L)</dt> -<dd>7.9, colorless, Japan (3801, L)</dd> -<dt>Datolite: 5.4, colorless, Massachusetts (3876, Boucot)</dt> -<dd>5, colorless, Massachusetts (3283, Sinkankas)</dd> -<dt>Diopside: 133, black (a star), India (3977)</dt> -<dd>24, black (a cat’s-eye), India (3956, Lea)</dd> -<dd>14, black (a cat’s-eye), India (3880)</dd> -<dd>11, green, Madagascar (2264, R)</dd> -<dd>6.8, yellow, Italy (3634)</dd> -<dd>4.6, yellow, Burma (3346, L)</dd> -<dd>2.2, pale green, New York (572, L)</dd> -<dd>1.6, green (chrome diopside), Finland (3693)</dd> -<dt class="pb" id="Page_74">74</dt> -<dt>Enstatite: 11, brown, Ceylon (3638)</dt> -<dd>8.1, brown, Ceylon (2294, R)</dd> -<dt>Epidote: 3.9, brown, Austria (579)</dt> -<dt>Euclase: 13, green, Brazil (3214, R)</dt> -<dd>9, yellow, Brazil (3215, R)</dd> -<dd>8.9, yellow, Brazil (2181, L)</dd> -<dd>3.7, blue-green, Brazil (3388, R)</dd> -<dt>Fluorite: 354, pale yellow, Illinois (3877)</dt> -<dd>125, green, New Hampshire (3294)</dd> -<dd>117, green, Africa (2153)</dd> -<dd>63, yellow, Illinois (3595, L)</dd> -<dd>33, colorless, Illinois (3626)</dd> -<dd>8.5, pink, Switzerland (3730, R)</dd> -<dt>Friedelite: 12, red-brown, New Jersey (3013, D’Ascenzo)</dt> -<dt>Gadolinite: 8.6, black, Texas (587, L)</dt> -<dt>Idocrase: 3.5, brown, Italy (4179, R)</dt> -<dt>Kyanite: 11, blue, Brazil (3557, L)</dt> -<dd>9.1, green, Brazil (3558, L)</dd> -<dd>3.7, blue, North Carolina (364, Bowman)</dd> -<dt>Kornerupine: 22, brown, Ceylon (3706, Lea)</dt> -<dd>11, brown, Madagascar (3567, L)</dd> -<dd>7.6, green, Madagascar (3782)</dd> -<dt>Labradorite: 11, pale yellow, Utah (3121)</dt> -<dt>Microlite: 3.7, brown, Virginia (3588, Lea)</dt> -<dt>Oligoclase: 6, colorless, North Carolina (404, L)</dt> -<dt>Orthoclase: 250, yellow, Madagascar (3878)</dt> -<dd>105, pale green (a cat’s-eye), Ceylon (3883)</dd> -<dd>61, yellow, Madagascar (1838, L)</dd> -<dd>26, gray (a cat’s-eye), Ceylon (3579, Lea)</dd> -<dd>23, white (a star), Ceylon (3578, L)</dd> -<dt>Petalite: 11, colorless, South-West Africa (3096)</dt> -<dt>Phenakite: 22, colorless, Russia (3739)</dt> -<dd>10, colorless, Brazil (2263, R)</dd> -<dt>Phosphophyllite: 5, green, Bolivia (3950, Roebling)</dt> -<dt>Pollucite: 9, colorless, Maine (2056, L)</dt> -<dd>7, colorless, Connecticut (3802, R)</dd> -<dt>Proustite: 9.9, red, Germany (4082, L)</dt> -<dt>Rhodizite: 0.5, colorless, Madagascar (3219, Canfield)</dt> -<dt>Rhodochrosite: 9.5, pink, South Africa (4189, L)</dt> -<dt>Samarskite: 6.6, black, North Carolina (588, L)</dt> -<dt>Scheelite: 37, colorless, California (3701, L)</dt> -<dd>12, gold, Mexico (3803, R)</dd> -<dt>Scorodite: 2.6, purple, South-West Africa (3793)</dt> -<dt>Sillimanite: 5.9, black (a cat’s-eye), South Carolina (3600, L)</dt> -<dt>Sinhalite: 110, brown, Ceylon (3587)</dt> -<dd>44, brown, Ceylon (3548, L)</dd> -<dt>Sphalerite: 73, yellow-brown, Utah (3556)</dt> -<dd>69, yellow-brown, Utah (3362)</dd> -<dd>60, yellow-green, New Jersey (3874, Roebling)</dd> -<dd>48, yellow, Mexico (2167, L)</dd> -<dd>46, yellow, Spain (3707, L)</dd> -<dt>Sphene: 0.8-9.3, sixteen stones, gold, Switzerland (2043, Nina Lea)</dt> -<dd>8.5, brown, New York (550)</dd> -<dd>5.6, yellow-brown, Mexico (3290)</dd> -<dd>5.2, yellow-brown, Mexico (3292)</dd> -<dt>Staurolite: 3, dark red-brown, Brazil (3795)</dt> -<dt>Tektite: 23, brown, Czechoslovakia (681, L)</dt> -<dt>Wernerite: 288, colorless, Burma (3783)</dt> -<dd>30, colorless (a cat’s-eye), Burma (3301, L)</dd> -<dd>29, pale yellow, Brazil (2098, L)</dd> -<dd>17, pink (a cat’s-eye), Ceylon (3238, Roebling)</dd> -<dd>12, pink, Burma (3674, L)</dd> -<dt>Willemite: 12, orange-yellow, New Jersey (1898, L)</dt> -<dd>11, orange-yellow, New Jersey (4187, Lea)</dd> -<dt>Zincite: 20, red, New Jersey (3386, R)</dt></dl> -<div class="img"> -<img src="images/p37.jpg" alt="Seal of the Smithsonian Institution" width="448" height="432" /> -</div> -<h2>Transcriber’s Notes</h2> -<ul> -<li>Silently corrected a few typos.</li> -<li>Retained publication information from the printed edition: this eBook is public-domain in the country of publication.</li> -<li>In the text versions only, text in <i>italics</i> is delimited by _underscores_.</li> -</ul> - - - - - - - -<pre> - - - - - -End of the Project Gutenberg EBook of Gems in the Smithsonian Institution, by -Paul E. 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