The beryl is a compound of silicates of beryllia and alumina, with the formula 3BeOSiO2 + Al2O3,3SiO2, or 3BeO,Al2O3,6SiO2. It differs very little indeed from the emerald, with the exception of its colour.
In the ordinary varieties this is somewhat poor, being mostly blue, or a dirty or a greenish yellow; the better kinds, however, possess magnificent colour and variety, such as in the aquamarine, emerald, etc.
The cleavage is parallel to the basal plane. Its lustre is sometimes resinous, sometimes vitreous, and it crystallises in the 2nd (hexagonal) system. It occurs in somewhat long, hexagonal prisms, with smooth, truncated planes, and is often found in granite and the silt brought down by rivers from granite, gneiss, and similar rocks.
It is found in Great Britain and in many parts of Europe, Asia, and America, in crystals of all sizes, from small to the weight of several tons. The common kinds are too opaque and colourless to be used as gems and are somewhat difficult of fusion under the blowpipe, on the application of which heat some stones lose their colour altogether, others partly; others, which before heating were somewhat transparent, become clouded and opaque; others suffer no change in colour, whilst some are improved. In almost every case a slight fusion is seen on the sharp edges of fractures, which become smooth, lose their sharpness, and have the appearance of partly fused glass.
The hardness varies from 7-1/4 to 8, the crystals being very brittle, breaking with a fracture of great unevenness. The better varieties are transparent, varying from that to translucent, and are called the “noble” beryls. Transparent beryl crystals are used by fortune-tellers as “gazing stones,” in which they claim to see visions of future events.
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