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PRECIOUS STONES
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solution
of violets, of which a drop only need he taken for test, is turned
green by adding to it a few grains of topaz dust, or of a little
splinter crushed to fine powder.
The Beryl. The beryl is a compound of silicates of beryllia and alumina, with the formula
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
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