AMETHYST. This name has been applied to two precious stones of essentially different natures. The Oriental Amethyst is a rare variety of Adamantine Spar [ADAMANTINE SPAR] or Corundum. The Occidental, or Common Amethyst, now to be described, is a variety of quartz or rock crystal, which is met with in many parts of the world, as India, Siberia, Sweden, Germany, Spain, &c. It occurs in various forms, as massive, in rounded pieces, and crystallised. Tho primary form of the crystal, like that of quart; is a slightly obtuse rhomboid, but it is usually found in the secondary form of a 6-sided prism, terminated at one or both ends by a 6-eided pyramid; some times, though rarely, the prism is wanting, end the pyramids being then united base to'base, the secondary crystal is a dodecahedron with triangular faces.
The amethyst is principally distinguished from common quartz by its colour, which is occasionally of every shade of violet, or rather purplish-violet, and this in the perfect amethyst Is pretty equal throughout the crystal : very commonly the summits only of the crystal are amethystine, the lower part being nearly colourless, or tinged with green. By long-continued heat the colour is destroyed
and the crystals become white and opalescent Sometimes the crystals' are aggregated or'faseiculeted ; in the Palatinate they are found lining geodes of agate, and in Silesia capillary crystals occur mixed with micaceous iron ore.
The crystals of the amethyst vary from diaphanous to translucent, and they exhibit various degrees of splendour, both externally and internally. The fracture is commonly conchoidal, and the fragments are of indeterminate form. Like quartz, the amethyst is sufficiently hard to give fire with steel and to scratch glass ; and has also been found, like it, with cavities containing water; it is infusible by the common blow-pipe. According to Hose, it consists of— Silica . ..... . 97'50 Alumina Oxide of Iron and Manganese . .