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emerald,the green variety of berylberyl
, mineral, a silicate of beryllium and aluminum, Be3Al2Si6O18, extremely hard, occurring in hexagonal crystals that may be of enormous size and are usually white, yellow, green, blue, or colorless.
..... Click the link for more information. , of which aquamarine is the blue variety. Chemically, it is a beryllium-aluminum silicate whose color is due to small quantities of chromium compounds. The emerald was highly esteemed in antiquity; the stones were used for ornaments in early Egypt where some of the first emeralds were mined. The finest emeralds are found in South America in Colombia, where they have been mined for over 400 years. The gem was a favorite in pre-Columbian Mexico and Peru, where it was cut in intricate designs. The treasure taken back to Spain by early explorers included emeralds. Good emeralds are the most highly valued of gem stones. Zambia and Brazil are also significant sources of the natural stones. Synthetic emeralds are also manufactured in Germany, France, and the United States. The Oriental emerald, a different gem, is the transparent green variety of corundumcorundum
, mineral, aluminum oxide, Al2O3. The clear varieties are used as gems and the opaque as abrasive materials. Corundum occurs in crystals of the hexagonal system and in masses. It is transparent to opaque and has a vitreous to adamantine luster.
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a mineral that is a transparent variety of beryl tinged with an admixture of Crj03 to a deep grass-green color. Emeralds are found in crystals and their concretions, usually intergrown in micaceous rock, quartz, or feldspar. The crystals, measuring 2–5 cm by 0.5–2 cm, rarely larger, are fractured. The larger deposits are connected with zones of the contact alteration of amphibolites, magnesial schist, and serpentinites by granitic pegmatites. Emeralds are also found in quartz feldspar veins and in altered schistose-carbonate rocks. Deposits are rare and are mainly in the USSR (Urals), Republic of South Africa (Transvaal), and Colombia (Muzo). Emeralds are highly valued as gems; those that are large (more than 5 carats), flawless, and have a deep, rich color are considered to be more valuable than diamonds.
Synthetic emeralds (so-called igmeralds) are made, but their crystals are often fissured and no larger than 0.5 by 3 cm.
["Distribution and Abstract Types in Emerald", A. Black et al, IEEE Trans Soft Eng SE-13(1):65-76 (Jan 1987)].