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Related to Gems: JEMS
GEMS(1) See Legato and GEMMS.
(2) (Global Election Management System) Electronic voting software from Dominion Voting Systems, Inc. GEMS was originally created by Premier Election Solutions, a Diebold subsidiary. Roughly 25% of votes cast in the U.S. employ this system, and there has been a lot of controversy over its use. GEMS was found to be easily compromised if election officials were not extremely careful. See e-voting.
a diverse group of minerals, divided into the precious stones proper and the semiprecious stones.
Precious stones are usually crystals. They may be either achromatic or finely colored with a rich luster. The degree of transparency varies. They are characterized by a high index of hardness (from 5 to 10 on the mineralogical scale), durability, high dispersion of light, purity of tone of coloration, and uniformity of color. For the most part they are cut. The brilliance of precious stones is determined by an optical property that is common to all minerals—a high coefficient of refraction. The luster and play of reflected rays are enhanced by expert cutting. The optical properties of opalescence and iridescence also are highly valued; they produce rich chatoyances of colors (for example, opal), asterisms (a gleam of light in the form of a six-rayed star, for example, in the star sapphire), changes in color under different illumination (for example, alexandrite), and pleochroisms (differences in coloration during transmission of light in different directions in the crystal). The hardness determines the durability, the capacity to preserve the polish, and the sharp angles and edges of the cutting. The value of precious stones is determined by their rarity (the expenditure of a considerable amount of labor locating and extracting them), by the high cost of cutting, and by individual qualities of the stones (for example, size, uniformity, beauty of color). Valuation, with consideration of the distinctive features of the stone, is done in carats (1 carat = 200 mg); for pearl the unit of valuation is the grain, which equals 0.25 carats.
Semiprecious stones include semitranslucent, frequently opaque mineral aggregates, rocks, and other mineral substances with colored inclusions or designs. They are used for large decorative articles (table tops, vases, wall panels, florentine mosaics), for small mountings and ornaments, and for technical purposes (for example, jasper, nephrite, malachite, agate, and fluorite). Semiprecious stones are classified according to their physical and mechanical properties as hard (5 and above on the mineralogical scale; for example, nephrite, jasper, and agate) or soft (4 and below in hardness; for example, malachite, onyx marble, steatite, fluorite). The value of the stones is also determined by their rarity, by individual properties (beauty of color, designs), and by the labor expended in processing. Valuation of the raw material, taking into account the individual properties of the stone, is made in kilograms and centners.
Classification. According to the classification of A. E. Fersman and M. Bauer, the two basic groups, precious and semiprecious stones, are subdivided into orders or classes (I, II, III), depending on the relative value of the stones. The precious stones of order I include diamond, sapphire, ruby, emerald, alexandrite, chrysoberyl, precious spinel, and euclase. Pearl is also included, as a precious stone of organic origin. Pure, transparent stones of uniform, rich tones are valued highly. Stones of this order that are poorly colored, blurred, cracked, and in other ways deficient may be valued below precious stones of order II.
The precious stones belonging to order II are topaz, beryl (aquamarine, vorobyevite, heliodor), pink tourmaline (rubellite), phenakite, demantoid garnet (ural chrysolite), amethyst, almandine, pyrope, uvarovite, chrome diopside, zircon (hyacinth, yellow and green zircon), and precious opal. Given exceptional beauty of tone, transparency, and size, these stones are sometimes valued equally with the gems of order I. Precious stones belonging to order III are turquoise, green and polychromatic tourmalines, cordierite, spodumene (kunzite), dioptase, epidote, rock crystal, smoky quartz (rauchtopaz), light amethyst, cambay stone, heliotrope, chrysoprase, semiopal, agate, feldspars (sunstone, moonstone), sodalite, prehnite, andalusite, diopside, hematite (blood stone), pyrite, rutile, amber, and gagate. Only rare forms and specimens of this group are of high value. Many of them are considered semiprecious in terms of both use and value.
Semiprecious stones of order I include nephrite, jadeite, lazurite, sodalite, glauconite, amazonite, labradorite, manganese spar (rhodonite), malachite, aventurine, quartzite, smoky quartz and rose quartz, chalcedony, prase, agate, jasper, vesuvianite (californite), and graphic granite (pegmatite). Semiprecious stones belonging to order II are serpentine, agalmatolite, steatite, selenite, anhydrite, obsidian, onyx marble (eastern onyx), fluorite, rock salt, and sepiolite. Semiprecious stones of order III include gypsum, alabaster, marble, porphyry, breccia, quartzite, and other rocks. This last sequence belongs more to the category of facing materials (decorative stones), which are used in architecture and artistic works. Various chemical dyes are applied to some precious and semiprecious stones to give brighter coloration (for example, red, black, and blue agates, cambay stone). The color of certain precious stones may be altered artificially before cutting by means of heating or radioactive irradiation, X rays, and ultraviolet rays (for example, achromatic diamond turns green under irradiation with radium).
Artificial and synthetic precious stones represent a special group of precious stones. Synthetic precious stones include diamond, emerald, corundum (sapphire, ruby), spinel, and achromatic rutile (imitating diamond in its luster). “Amethysts,” “alexandrites,” “aquamarines,” and other stones are produced by coloring synthetic corundum and spinel by introducing admixtures of chromium, titanium, vanadium, and iron. All varieties of crystalline quartz, such as rock crystal and amethyst, can be made for cutting by synthetic means. Numerous imitations of precious stones exist. It is necessary to make a distinction between imitation (artificial) and synthetic stones. The latter are identical or close to natural precious stones. Imitations are made of paste, glass scoria (colored with various additives), and plastic (especially for amber imitations).
Historical survey References to precious stones as the embodiment of luxury in literary sources of Egypt, Iran, Judeah, and India attest to the fact that even in ancient times people valued the natural beauty and rareness of gems. However, skill in bringing out through processing (polishing, cutting) the luster of the stone, the play of its facets, its transparency, and its complete colorlessness or the bright color developed considerably later. In the East the art of cutting gems comes from India. Diamonds cut in ancient times are referred to as having Indian faceting. In Europe during the early Middle Ages the art of gem polishing was mastered; external impurities and cloudiness were removed from the stone, crystals were freed from rocks, emphasizing their natural facets or natural roundness, making them similar to cabochon (a rounded stone with smoothed facets). Processed gems were fastened to the objects being decorated by means of plain or filigreed metal settings, which sometimes had supplementary clamps. In 1456 the Dutchman Ludwig van Berquen became the first to use diamond dust to cut diamonds with intricate facets. This method was soon adopted for cutting other hard stones. During the Renaissance diamonds and gems customarily were cut until an even surface, or table, was obtained; they were then fixed in the setting by finely grinding or grooving the edges of the stone in order to give the stone maximum exposure. Cabochons predominated in Russia as late as the 18th century. The art of cutting was established in the beginning of the 18th century by foreign masters. Gravero was famous for his skill in diamond cutting in the first quarter of the 18th century. In 1725 the Diamond Mill was founded in Petergof by an edict of Peter I; it consisted of a polishing factory specializing first in gem cutting and later (beginning with the end of the century) in preparing decorative articles from jasper and agate as well, such as various florentine panels, so-called Russian mosaics, and utilitarian and decorative artistic pieces, which are now preserved in museums such as the Hermitage. The cutting of gems, however, remained in the hands of individual masters. The passion for the brilliant-cut diamond that began in the early 18th century had a notable effect on the processing of other gems. The upper part of colored stones were polished in the brilliant style, with a large “table,” the lower parts, in steps or hemispheres. Stones with iridescent surfaces (opals, chrysoprases, tiger’s eye) and turquoise were polished in cabochon. Mountings were increasingly made of silver (and, since the second half of the 19th century, platinum) in order to avoid the color changes of the stone that occur if gold is used for mounting or bracing. The mountings of colored stones were frequently decorated with small brilliants, which hid the metal and through their play deepened the color and play of the stone. Gems are processed in the same way in 20th-century jewelry making.
Deposits Gem deposits are the result of a broad complex of natural processes. The formation of primary deposits of precious and semiprecious stones is the result of the following processes: (a) the crystallization of basic abyssal magma, rich in magnesium and iron (diamond, pyrope, and others), (b) the crystallization in granite pegmatites of various genetic types (beryl, emerald, aquamarine, zircon, topaz, tourmaline, amazonite), (c) the crystallization of hot and cold mineralized aqueous solutions of surface or subsurface origin (opal, rock crystal, amethyst, turquoise, agate, malachite), (d) formation in metamorphic and contact-metasomatic deposits (ruby, sapphire, spinel, lazurite, granite, jadeite). Mining areas are frequently connected with placers that appeared with the destruction of the bedrock in which the minerals had formed. Some gems are of organogenic origin (pearl, amber).
Deposits of gems of various genetic types are widespread throughout the world. Russia has long been famed for her deposits of precious and semiprecious stones. Remarkable deposits of colored jasper in the Ural Region and in the Altai yield the world’s finest (in terms of beauty and block size) materials for large artistic works. Green malachite and red manganese spar with beautiful black designs from deposits in the Urals, nephrite from the Eastern Saians, and dark blue lazurite from the Baikal Region are the world’s finest stones in terms of both beauty and technical virtues.
An enormous amount of the most diverse (in design and coloration) marble has been discovered and is being mined in deposits of the Ukraine, the Ural Region, Karelia, the Caucasus and Transcaucasia, Middle Asia, and Eastern and Western Siberia. Onyx marble of beautiful design and coloration is found in deposits in Armenia and Uzbekistan. There are deposits of agate and chalcedony in Transcaucasia and Eastern Siberia. Equally well-known are the light blue, sea-color “Siberian aquamarines” from deposits in the Ural Region and Eastern Siberia. Ural emerald, topaz of various shades, and Ural amethysts are considered the finest of their class in color and quality. The world’s largest deposits of amber are found in Kaliningrad Oblast. Deposits of turquoise have been discovered in Middle Asia, diamonds in Ural and Yakutsk deposits, fire opal in Kazakhstan, and rock crystal (some of which is being cut) in the Ural Region, the Pamirs, Kazakhstan, and Eastern Siberia.
The following are also highly valued: Ural alexandrite (green in the daylight and wine-red under artificial illumination), bright pink sibirite (tourmaline from deposits in the Ural Region and Siberia), brilliant phenakites that resemble diamonds, and emerald-green demantoid garnet.
Deposits of precious and semiprecious stones are known in Africa, South America, Asia, Europe, and Australia, but mining of these deposits is unevenly distributed. The diamonds of South Africa constitute nearly 90 percent of the value of all precious stones being mined in foreign countries. The greatest quantity and variety of precious and colored stones (not including the diamonds of South Africa) are produced by Asia, followed by South America, Africa (including Madagascar), Europe, and Australia. In Africa and on the island of Madagascar there is mining of diamonds, emeralds, beryl, aquamarine, tourmaline, rock crystal, topaz, and pyrope. South America (mainly Brazil and Colombia) is a large supplier of emerald, beryl, aquamarine, pink topaz, amethyst, agate, phenakite, diamond, and tourmaline. In the countries of Asia there are notable deposits of nephrite (China), turquoise, lazurite (Iran, Afghanistan), diamond, sapphire, ruby, spinel, zircon, jadeite, and almandine (India, Sri Lanka, Thailand). Certain European countries are famous for red pyrope garnet (Czechoslovakia), marble, breccia and other precious stones (Greece, Sweden, Italy), fluorite (Great Britain), and precious opal (Hungary and Czechoslovakia). Opal is mined in Australia. North America has relatively few precious stones (pink beryl, polychromatic tourmaline, and low-grade turquoise).
Uses The use of gems in the development of precision instruments and specialized branches of industry (the radio industry and others) has changed considerably. The use of natural stones for jewelry and decorative and artistic purposes has fallen sharply. Technology has been developed for the manufacture of synthetic stones (ruby, sapphire, spinel) and all possible inexpensive fakes and imitations. A large share of precious stones is being used for industrial purposes, where their consumption is ever growing. Thanks to their considerable hardness, diamonds are widely used in drilling, for cutting and polishing hard materials, and for other purposes. Rubies and sapphires (for the most part synthetic) are used in watchmaking and as step bearings in precision mechanisms. Transparent quartz and tourmaline are used widely for special optical instruments and in the radio industry. Agate, chalcedony, and varieties of them are being used in large quantities in the manufacture of parts for precision weights and measuring instruments, as well as for chemical mortars and step bearings. The new technology in the manufacture of precision instruments and in the optical, watch-making, and radio electronics industries has generated a demand for the harder precious stones (ruby, sapphire, corundum, tourmaline, topaz, quartz, fluorite).
Since ancient times precious and semiprecious stones have been used along with shells, bone, horns, and wood in making beads, pendants, bracelets, and amulets. They have also been widely used as a material for the fine plastic arts (for example, glyptics, carving, and sculpture), for inlaying furniture, facing vases and boxes (mainly malachite), and producing handles for knives, spoons, and forks. In jewelry, gems often take on independent artistic value as the basic part of the jewel.
REFERENCESFersman, A. E. Samotsvety Rossii, vols. 1-2. Pskov, 1921.
Fersman, A. E. “Dragotsennye i tsvetnye kamni.” In Nerudnye iskopaemye, vol. 1. Leningrad, 1926.
Fersman, A. E. Ocherki po istorii kamnia, vol. 1. Moscow, 1954.
Merenkov, B. la. Dragotsennye tekhnicheskie ipodelochnye kamni. Moscow-Leningrad, 1936.
Diukalov, N. A. Mirovaia torgovlia dragotsennymi i poludragotsennymi kamniami. Moscow-Leningrad, 1932.
Petrov, V. S. Dragotsennye i tsvetnye kamni. Moscow, 1963.
G. P. BARSANOV and M. I. TORNEUS