EMERALD, a bright green variety of beryl, valued as a gem-stone. The name comes indirectly from the Gr. apapa'ySos (Arabic zumurrud), but seems to have been given to a number of stones having little in common except a green colour.
The properties of emerald are mostly the same as those of beryl. The crystals often show simply the hexagonal prism and basal plane. The prisms cleave, though imperfectly, at right angles to the geometrical axis ; and hexagonal slices were formerly worn in the East. Compared with most gems, the emerald is rather soft, its hardness (7.5) being but slightly above that of quartz. The specific gravity is low, varying slightly in stones from different localities, but being for the Muzo emerald about 2.67. The refrac tive and dispersive powers are not high, so that cut stones show little "fire." The colour is probably due to chromium. F. Wohler found 0.186% of in the emerald of Muzo—a proportion sufficient to impart an emerald-green colour to glass.
The ancients appear to have obtained the emerald from Upper Egypt, where it is said to have been worked as early as 1650 B.C. It is known that Greek miners were at work in the time of Alex ander the Great, and in later times the mines yielded their gems to Cleopatra. Remains of extensive workings were discovered in the northern Etbai by the French traveller, F. Cailliaud, in 1817, and the mines were re-opened for a short time under Mohammed Ali. "Cleopatra's Mines" are situated in Jebel Sikait and Jebel Zabara near the Red sea coast east of Aswan. They were visited in 1891 by E. A. Floyer, and the Sikait workings were explored in 1900 by D. A. MacAlister and others. The Egyptian emeralds occur in mica-schist and talc-schist.
On the Spanish conquest of South America vast quantities of emeralds were taken from the Peruvians, but the exact locality which yielded the stones was never discovered. The only South American emeralds now known occur near Bogota, the capital of Colombia. The most famous mine is at Muzo, but workings are known also at Coscuez and Somondoco. The emerald occurs in nests of calcite in a black bituminous limestone containing ammon ites of Lower Cretaceous age. The mineral is associated with quartz, dolomite, pyrites and the rare mineral parisite (q.v.), named after J. J. Paris, who worked the emeralds.
In 1830 emeralds were discovered in the Ural mountains and have been worked on the river Takovaya, about 6om. N.E. of Ekaterinburg, where they occur in mica-schist, associated with aquamarine, alexandrite, phenakite, etc. Emerald is found also in mica-schist in the Habachthal, in the Salzburg Alps, and in granite at Eidsvold in Norway. Emerald has been worked in a vein of pegmatite, piercing slaty rocks, near Emmaville, in New South Wales. The crystals occurred in association with topaz, fluorspar and cassiterite; but they were mostly of rather pale colour. In the United States, emerald has occasionally been found and fine crys tals have been obtained from the workings for hiddenite at Stony point, Alexander county, N.C.
Many virtues were formerly ascribed to the emerald. When worn, it was held to be a preservative against epilepsy, it cured dysentery, it assisted women in childbirth, it drove away evil spirits, and preserved the chastity of the wearer. It was reputed to have medicinal value, and because of its colour was said to be good for the eyesight.