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Ch. 6: Quartz Amethyst

Ch. 6: Quartz Amethyst Page of 515 Ch. 6: Quartz Amethyst Text size:minus plus Restore normal size   Mail page  Print this page
260                  A POPULAR TREATISE ON GEMS.
double six-sided pyramid. Quartz scratches glass and felspar, but is attacked by topaz. Its hardness is 7.0, and its specific gravity, 2.5 to 2.7 ; it is transparent, and possesses a vitreous lustre; becomes electric by rubbing; is infusible before the blowpipe. Acids, except the fluoric acid, do not act upon it. Silica is the only essential com­ponent part of quartz, but some varieties contain iron, alu-mine, or lime.
ROCK CRYSTAL. •
This mineral was known in early ages. It was highly esteemed by the Greeks on account of its purity and very regular formation. Theophrastes states that it was "cut principally as seals, and the ancients made great use of it for ornaments, particularly before the art of making glass had reached much perfection. Among the many vessels which were cut in the- form of cups, vases, &c, were two fine bowls and chalices in the possession of the tyrant Nero, who purchased them at a large sum. Rock crystal was also used as a medicine.
It is found crystallized, in the primitive form, which is the rhomboid, extended to a six-sided prism; and in a great variety of forms and modifications, such as with a trunca­tion or replacement of the edges, or solid angles, &c. It is frequently found in groups, also in the cavities of other minerals, or in incrustations, as small, but very perfect crystals, the pyramidal terminations of which have a high polish, and the specimen' appearing as if it were studded with gems. Many specimens of this description were brought from Vermont a few year's ago, and were eagerly purchased by the jewellers of this city for rings, car-rings, and breastpins. Rock crystal has a conchoidal frac­ture ; is translucent and transparent; possesses a double refraction of light; a perfect vitreous lustre; is limpid,
Ch. 6: Quartz Amethyst Page of 515 Ch. 6: Quartz Amethyst
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