kinds under three heads : first, Vitreous quartz, comprising
crystal, amethyst, citrine, cairngorm, iris, rubasse, aventurine,
and prase ; second, Chalcedonyx, including carnelian, chalcedony, sardonyx, sard, onyx, nicolo, plasma, heliotrope, agate,
mocha-stone (a variety of agate), cat's-eye, and Chrysoprase;
the third division, called Jasper-quartz, embraces bloodstone
(differing from heliotrope), jasper, Egyptian pebbles, and porcellanite. King places aventurine with the jasper series.
Yellow quartz is sometimes called Scotch topaz, and Bohemian topaz, and the rose, Brazilian ruby, occasionally sold for
spinel ; the blue variety has frequently passed for water-sapphire, while specimens of brownish red are known as hyacinth
of Compostella, and when impregnated with bituminous substances they are denominated smoky quartz, cairngorm, and
Alençon diamonds.
Rock-crystal, or hyalin quartz, is the purest form of this
mineral known among lapidaries, and is recognized by various
names, as Bristol, Welsh, Irish, Cornish, and California diamonds, and sometimes it is employed in jewelry under the
title of "white stone." It received the appellation of crystal
("ice"), from the nations of antiquity, who supposed it was
formed by the excessive congelation of water, such as could be
found only in the coldest regions. Claudianus, one of their
writers, calls it " ice hardened into stone, which no frost could
congeal nor dog-star dry up." Orpheus poetically calls the crystal "the translucent image of the Eternal Light," and suggests
its use as a burning-glass to light the sacrificial flame. The
East Indian believes it to be the mother or husk of the
diamond.
The cavities frequently found in rock-crystals are sometimes
filled with a fluid or gas which has given rise to some speculation ; most scientists have thought it was water, but the
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