Beryl, a double silicate of aluminium and the rare metal beryllium or glucinum. It crystallises in hexagonal prisms with basal planes, often deeply striated longitudinally. These crystals sometimes reach enormous dimensions, being found at Grafton, New Hampshire, four to six feet long, and weighing 2,000 to 3,000 lbs. The hardness of the mineral ranges from 7.5 to 8, and its gravity from 2.63 to 2.75. It is brittle and has sometimes a conchoidal fracture: its streak is white; its lustre, vitreous or resinous; and it is almost infusible. It may be transparent and colourless; but is more often only translucent and bluish-green (aquamarine) or bright green (emerald), from the presence of a trace of oxide of chromium. Large crystals are generally opaque. Beryls were worked by the ancient Egyptians, and engraved as gems by the Greeks and Romans. Good gems are obtained at Mursinsk and Nertchinsk in the Urals, Canjargum in Hindustan, and Rio San Matteo in Brazil; but the locality for the finest emeralds is Muzo, about 70 miles from Santa Fe de Bogota, New Granada.