Note: ☞ 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.
Etymology: G. quarz