Title: Gems in the Smithsonian Institution
Author: Paul E. Desautels
Release date: August 8, 2020 [eBook #62879]
Most recently updated: October 18, 2024
Language: English
Credits: Produced by Stephen Hutcheson and the Online Distributed
Proofreading Team at https://www.pgdp.net
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.)
by PAUL E. DESAUTELS
Associate Curator
Division of Mineralogy
WASHINGTON, D. C.
1965
SMITHSONIAN
INSTITUTION
PUBLICATION
No. 4608
LIBRARY OF CONGRESS
Card No. 65-60068
Prof. F. W. Clarke, former honorary curator of the Division of Mineralogy who assembled the Smithsonian Institution’s first gem collection in 1884.
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.
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.
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.
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.
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 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.
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.
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.)
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.
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 depends mainly on its rarity and its beautiful play of colors to be considered gem material.
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.
When a gemologist or a gem cutter examines an unworked mineral fragment (called rough) 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.
| Scale of Hardness | |
|---|---|
| Soft | 1. Talc |
| ^ | 2. Gypsum |
| 3. Calcite | |
| 4. Fluorite | |
| 5. Apatite | |
| 6. Feldspar | |
| 7. Quartz | |
| 8. Topaz | |
| v | 9. Corundum |
| Hard | 10. Diamond |
It is difficult to list these characteristics in the order of importance, but hardness 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 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.
The size of a gemstone usually is indicated by its weight 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.
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.
Among the most striking and useful of the distinguishing characteristics of gemstones are those that involve the effects on light.
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. 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).
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).
Gemstones such as beryl and sapphire that depend on impurities for their color are said to be allochromatic; others, such as peridot and garnet, which are highly colored even when pure, are said to be idiochromatic. The color of a gem is further described according to its hue, tint, and intensity. 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.
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.)
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.)
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 chatoyancy or silky sheen of tiger’s-eye and cat’s-eye, the opalescence or pearly reflections of opal and moonstone, and the asterism or star effect of rubies and sapphires are caused by the reaction of light to minute inclusions or imperfections in the gemstone.
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.
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.
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.
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 (refraction) 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 refractive index of the gemstone.
Many gemstones can split a beam of light and bend one part more than the other, thus producing double refraction, or two different measurements of refractive index.
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.
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 dispersion or fire. 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.
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:
| Diamond | Carbon | C |
| Sapphire | Aluminum oxide | Al₂O₃ |
| Quartz | Silicon dioxide | SiO₂ |
| Emerald | Beryllium aluminum silicate | Be₃Al₂(SiO₃)₆ |
| Spinel | Magnesium aluminate | Mg(AlO₂)₂ |
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.
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.
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.
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 tumbled, gemstones recently have returned to fashion, the finest pieces of gem rough are now converted mainly into faceted, 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 brilliant cut, which is most commonly used to best bring out the qualities of a diamond.
The standard brilliant cut, with a pattern of many facets, is commonly used for gemstones having a high refractive index and, therefore, great brilliance.
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.
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.
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.
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.
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.
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 through the table 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.
The English brilliant cut has 28 crown and pavilion facets—28 fewer than the standard brilliant cut.
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.
For other purposes and for other kinds of precious stones a number of basic cuts have been developed. The brilliant and step 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.
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.
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.
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).
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.
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, 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.
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.
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.)
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.)
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 cabochons. 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.
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.
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.
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.
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.
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.
In general, gem substitutes can be classified as imitation stones, assembled stones, reconstructed and altered stones, and synthetic stones.
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.
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.
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.
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.
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.
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.
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.
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 fancies.
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 greened amethyst.
All of this tampering with gemstones complicates the problem of identification, so it is a matter of serious concern to the gem trade.
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.
Two of the basic techniques used in producing synthetic gems are the flame-fusion and the hydrothermal processes.
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).
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 boule 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 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.
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.
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.
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.
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 plate are mounted twelve stones representing the Twelve Tribes of Israel. Among Christians, the Twelve Apostles also were represented symbolically by precious stones.
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.
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.
Perhaps in our own space-oriented times the ancient superstitions sympathetically relating certain gemstones with the 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.
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.
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.
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.
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.
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.
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.