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Encyclopedia Britannica - Main :: BER-BLA |
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BERYL , a mineral
formula
Beryl crystallizes in the hexagonal system, usually taking the form of long six-sided prisms, striated vertically and terminated817 with the basal plane, sometimes associated with various pyramidal faces (see fig.). It cleaves rather imperfectly parallel to the base. The colour of beryl may he blue, green, yellow, brown or rarely pink
mineral
Beryl was much prized as a gem-stone by the ancients, and Greek intaglios o very fine workmanship are extant. The Roman jewellers, taking advantage of the columnar form of the natural crystal, worked it into long cylinders for ear-pendants. It was a favourite stone with the artists of the Renaissance, but in modern times has lost popularity, except in the form of emerald, which remains one of the most valued gem-stones. It is notable that English lapidaries of the 18th century often included the sard under the term beryla practice which has led to some confusion in the nomenclature of engraved gems. Beryl occurs as an accessory constituent of many granitic rocks, especially in veins of pegmatite, whilst it is found also in gneiss and in mica: schist. Rolled pebbles of beryl occur, with topaz, in Brazil, especially in the province of Minas Geraes. Crystals are found in drusy cavities in granite in the Urals, not-ably near Mursinka; in the Altai Mountains, which have yielded very long prismatic crystals; and in the mining district
Nerchinsk in Siberia, principally in the Adun-Chalon range, where beryl occurs in veins of topaz-rock piercing granite. Among European localities may be mentioned Elba, good crystals being occasionally found in the tourmaline-granite of San Piero. In Ireland excellent crystals of beryl occur in druses
Cornwall
Mount
Many localities in the United States yield beryl, sometimes sufficiently fine to be cut as a gem. It is found, for example, at Hiddenite and elsewhere in Alexander county, N.C.; at Haddam and Monroe, Conn.; at Stoneham and at Albany, in Oxford county, Maine; at Royalston, Mass.; and at Mt. Antero, Colorado, where it occurs with phenacite. Beryl of beautiful pink
Beryl suffers alteration by weathering, and may thus pass into kaolin
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