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Ch. 15: The Beryl Group

Ch. 14: Chrysoberyl Page of 187 Ch. 15: The Beryl Group Text size:minus plus Restore normal size   Mail page  Print this page
     
     
 
Chapter XV
  
 
 
  
 
BERYL
Introduction
 
BERYL has been known from ancient times, but the name was applied to a variety of stones, and its correct use came into vogue only about the end of the eighteenth century, because beryllium was discovered only in 1798 and the metal extracted in 1828. The metal is very light, but hard and silver-white. There is a great demand for beryllium for making light alloys for construction of aeroplanes, which has, in turn, created a great demand for beryl since the war started.
Physical Properties
Beryl is an alumino-silicate and includes the emerald aquamarine, golden beryl and morganite. Crystals of beryl form well-shaped hexagonal prisms terminated by basal planes. Sometimes they form enormous crystals weighing even a few tons. But such crystals are coarse and opaque and are of no value as gems, but form the ore of beryllium. The faces are striated parallel to its length. Common beryl is dull and opaque and is pale green or yellow in colour. Gem qualities—emerald is grass-green, but stones with such colours as pale green, yellowish green, bluish green to deep blue are called aquamarine. Specific gravity = according to variation in composition.
Hardness = to 8. Fracture: conchoidal to uneven. Lustre: Vitreous. Refractive index: ;
€ = Dichroism distinct, but not strong.
Uniaxial and negative. Composition: Beryllium is replaced by alkalies, lithium, sodium, potas­sium and caesium.
Uses
Ordinary beryl is not useful as a gem-stone, but is useful for the extraction of beryllium, which is an extra-
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Ch. 14: Chrysoberyl Page of 187 Ch. 15: The Beryl Group
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