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EMERALD.
203
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This
variety of corundum is very remarkable in being softer than the red and
blue stones, and it would seem that the glucine which enters into its
composition is the cause.
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It: crystallizes in regular prisms having six faces, besides which may
be seen various truncations ; its cleavage is straight and quadruple,
which property makes it easily distinguishable from other emeralds
which have no cleavage. All Oriental emeralds have not the same degree
of hardness ; their specific gravity, although it may differ from that
of other corundums, yet in the hardest varieties often amounts to 3.01.
The
perfect corundum is of an herbaceous green, more or less dark, which by
its silken light reposes and renews the sight. When analysed, it
generally yields
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Sometimes
it gives in the residue a little oxide of iron. There were caverns of
it in the island of Ceylon, at a place called Matoüla, but now they
seem exhausted; even there they were seldom found in large crystals.
This gem, when perfect and weighing more than two carats, is as valuable as the diamond.
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