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quartz

(Science: chemical) A form of silica, or silicon dioxide (SiO2), occurring in hexagonal crystals, which are commonly colourless and transparent, but sometimes also yellow, brown, purple, green, and of other colours; also in cryptocrystalline massive forms varying in colour and degree of transparency, being sometimes opaque.

The crystalline varieties include: amethyst, violet; citrine and false topaz, pale yellow; rock crystal, transparent and colourless or nearly so; rose quartz, rosecoloured; smoky quartz, smoky brown. The chief crypto-crystalline varieties are: agate, a chalcedony in layers or clouded with different colours, including the onyx and sardonyx; carnelian and sard, red or flesh-coloured chalcedony; chalcedony, nearly white, and waxy in luster; chrysoprase, an apple-green chalcedony; flint, hornstone, basanite, or touchstone, brown to black in colour and compact in texture; heliotrope, green dotted with red; jasper, opaque, red yellow, or brown, coloured 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 [[mak 478 es]] most of the sand of the seashore.

Origin: G. Quarz.