The
Hindoos regard rock crystal a specific for consumption, leprosy, and
poisoning. It is known among them as "unripe diamond," and may be
substituted in medicine for diamond.
Amethyst. This
term is applied to the violet or purple varieties of quartz. It is
derived from two Greek words meaning " not to inebriate," and
indicates the belief of the ancients that wine drunk from cups made of
this mineral could never have any deleterious effect. All degrees of
color are to be found in amethyst, from that only slightly tinted to
that so dark as to be almost opaque. The color may be irregularly
distributed, being sometimes in spots and again shading uniformly in
the same crystal from light to dark. Of these colors the dark
reddish-purple is the most highly esteemed, the paler stones being less
sought after. A reason for this is to be found in the fact that by
artificial light, especially if this contains yellow rays, pale stones
lose their violet color and become a dull gray. The deeply colored
amethysts, however, especially such as have been found in Maine, change
to a wine color by artificial light, and thus their beauty is enhanced.
Besides being of a deep purple color, a good amethyst should be
perfectly transparent and uniform in hue throughout. The nature of the
coloring matter of amethyst is not known. For a long time it was
thought to be oxide of manganese; but as the color disappears on
heating it is now believed to be a form of organic matter. It has been
noticed in some places where amethyst is mined that the most deeply
colored stones are at the surface, and that their color grows paler as
the vein is followed downward. The cause of this phenomenon is not
known. By partial heating the color of amethyst can be changed to
yellow, and some of the so-called citrine is made in this way.
Much
opaque and coarse quartz has an amethystine color, but such is
obviously of no value for gem purposes. The chief supply of the
amethysts used for jewelry at the present time comes from Siberia and
Brazil. The Siberian mines are located in the Urals in the vicinity of
Mursinka and Alabashka. The amethyst occurs in cavities in granite,
accompanied by beryl and topaz. Much of it is near the surface, and it
is also found lying loose.' The Brazilian amethysts occur partly in
cavities in a black eruptive rock (melaphyre), and partly as pebbles in
the river gravels, accompanied by chrysoberyl, topaz, etc. Amethyst of
gem quality is also found in Ceylon in gem gravels.
In
our own country amethyst occurs abundantly, but not often of the best
quality for cutting. Some of the finest amethyst known has come from
Oxford County, Maine, but only a few specimens have thus far
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