100 A Book of Precious Stones
The
chief sources of supply for amethysts are Brazil and the Ural
Mountains, Siberia. The Siberian amethysts, accompanied by beryl and
topaz, occur in cavities in granite; often they are found lying loose
and sometimes very near the surface. Cavities in a black eruptive rock
(melaphyre) are the hiding places of some Brazilian amethysts, while
others are found as pebbles in the river gravels with chrysoberyl and
topaz as companion minerals. Gem amethysts are also found in gravel
bearing other gems in Ceylon.
In
North America, a few of the finest specimens of amethyst on record
have been found in Oxford County, Maine. Other localities are Delaware
and Chester Counties, Pennsylvania, and Haywood County, North Carolina.
Crystallised amethyst in commercial quantities has been found at
Thunder Bay on the north shore of Lake Superior. The crystals are
highly coloured but not uniform or clear and few good gems have been
obtained there.
Amethyst
was formerly much more highly prized than now because of its scarcity.
Besides the increased supply it has been imitated so convincingly as
to impose upon all excepting gem experts. A celebrated amethyst necklace
