(n.) 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.

amphibole antimony apatite aplite arsenic asbestos asphalt azurite bauxite billiard table bitumen boron bowling alley bowling green brimstone bromine brucite calcite carbon celestite chalcedony chalk chlorite chromite clay coal coke corundum cryolite diatomite driven snow emery epidote epsomite feldspar flat fleece flour foam garnet glass glauconite graphite gypsum hatchettine holosiderite ice iron pyrites ivory jet kyanite level lignite lily lime maggot magnesite mahogany malachite maltha marble marcasite marl meerschaum mica milk mineral coal mineral oil mineral salt mineral tallow mineral tar mineral wax molybdenite monazite obsidian olivine ozokerite paper pearl peat perlite phosphate rock phosphorus plane pumice pyrite pyrites pyroxene quartz realgar red clay rhodonite rock crystal rocks salt satin selenite selenium sheet siderite silica silicate silicon silk silver slide smooth snow spar spinel spodumene sulfur swan talc talcum tellurium tennis court velvet wollastonite wulfenite zeolite