EMERALD (Sp. esmeralda, Fr. emeraude, Ger. maraud, Gr. smaragdos; the name is originally Semitic, or at least eastern, but the signification unknown), a mineral generally regarded by mineralogists as merely another variety of the same species with the beryl (q.v.), with which it essentially agrees in composition, crystallization, etc., differing in almost nothing but color. The E., which, as a gem, is very highly valued, owes its value chiefly to its extremely beautiful velvety green color. It is composed of about 67 to 68 per cent of silica, 15 to 18 of alumina, 12 to 14 of glucina, and a very little per oxide of iron, lime, and oxide of chromium. Its color is ascribed chiefly to the oxide of chromium which it contains. Its specific gravity is 2.577 to 2.725. In hardness it is rather inferior to topaz. The localities in which E. is found are very few. The finest have long been brought from South America, where they are obtained from veins traversing clay-slate, hornblende slate, and granite, in a valley not far from Santa F'& de Bogota. Emeralds of inferior quality are found in Europe, imbedded in mica-slate in the Henbach Valley in Salzburg. They are also found in the Ural ; and sonic old
mines in Upper Egypt have also been discovered to yield them, from which, probably, the ancients obtained them. This gem, known from very early times, was highly prized by the ancients. Pliny states that when Lucullus landed at Alexandria, Ptolemy offered him an E. set in gold, with his portrait engraven on it. Many wrought emeralds have been found in the ruins of Thebes. Nero, who was near-sighted, looked at the combats of gladiators through an eye-glasa, of E., and concave eye-glasses of E. seem to have been particularly esteemed among the ancients. As a precious stone, the E. is rarely without flaw. Its value also depends much on its color. A very perfect E. of six carats has been sold for £1000.
It appears not improbable that emeralds have been found in the east, in localities not at present known, but the name E. or ORIENTAL .E. is often given to a very rare, beautiful, and precious green variety of sapphire (q.v.).