VIII.
THE AMETHYST.
The amethyst, like all gems, is both Oriental and Western.
The
Oriental amethyst is a clear corundum of a violet colour, somewhat
reddish and of an elegant velvetlike appearance ; very bright; perhaps
less hard than the ruby; specific gravity 4; of weak double refraction
; and it cuts deeply into the rock crystal. The Western amethyst can be
distinguished from it by the fact that when rubbed it preserves
vitreous electricity but twenty or thirty minutes, whereas the Oriental
preserves it for many hours.
The
Western j amethyst is a clear quartz, coloured violet by the oxide of
manganese which it contains: of the specific gravity of 2-7,
it crystallizes in the form of a hexagon, terminated at the two heads
by a species of cone with six facets. These crystals are often in
masses, and the base is always less coloured than the top. The cleavage
in one of such masses appears fibrous and concave in crystals of small
size. The colour is more or less dark, and does not resist fire. This
gem possesses double refraction, but in a moderate degree. It is
motionless under the magnetic needle.
It
may be remarked that amethysts are generally found in metalliferous
mountains, and are always in combination with quartz and agate. This
substance is found in Ceylon, Siberia, Kamtschatka, Arabia, Brazil,
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