Quartz (?), n. [G. quarz.]
(Min.) A form of silica, or silicon dioxide
(SiO2), occurring in hexagonal crystals, which are commonly
colorless and transparent, but sometimes also yellow, brown, purple,
green, and of other colors; also in cryptocrystalline massive forms
varying in color and degree of transparency, being sometimes
opaque.
&fist; The crystalline varieties include: amethyst,
violet; citrine and false topaz, pale yellow;
rock crystal, transparent and colorless or nearly so; rose
quartz, rosecolored; smoky quartz, smoky brown. The chief
crypto-crystalline varieties are: agate, a chalcedony in layers
or clouded with different colors, including the onyx and
sardonyx; carnelian and sard, red or flesh-
colored chalcedony; chalcedony, nearly white, and waxy in
luster; chrysoprase, an apple-green chalcedony; flint,
hornstone, basanite, or touchstone, brown to
black in color and compact in texture; heliotrope, green dotted
with red; jasper, opaque, red yellow, or brown, colored by iron
or ferruginous clay; prase, translucent and dull leek-green.
Quartz is an essential constituent of granite, and abounds in rocks of
all ages. It forms the rocks quartzite (quartz rock) and
sandstone, and makes most of the sand of the seashore.
