BERYL, the name applied to the species of precious stone including the emerald (q.v.), the aquamarine (q.v.) and other transparent varieties known as "precious beryl," with certain coarse opaque varieties unfit for use as gem-stones. The name comes from the Gr. (37)pvXXos, a word of uncertain etymology applied to the beryl and probably several other gems (see GEMS). Beryl is a silicate of beryllium and aluminium, alkalis (Na, IL, Li, Cs) sometimes replace Be up to a maximum of 7%. It crystallizes in the hexagonal system, usually taking the form of long six-sided prisms, striated vertically and termi nated by the basal plane, sometimes associated with various pyramidal faces. It cleaves rather imperfectly parallel to the base. The colour may be blue, green, yellow, brown, colourless or rarely pink. The specific gravity is about 2.7, and the hardness 7.5 to 8. The transparent crystals are pleochroic—a character well marked in emerald.
Beryl occurs as an accessory constituent of many granitic rocks, especially in veins of pegmatite, while 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, notably near Mursinka ; in the Altai mountains, which have yielded very long prismatic crystals; in the mining district of Nerchinsk in Si beria, principally in the Adun-Chalon range, where beryl occurs in veins of topaz-rock piercing granite; in Cornwall, Ireland, Scot land and other parts of Europe; and in many parts of the United States.