/sil"i keuh/, n.the dioxide form of silicon, SiO2, occurring esp. as quartz sand, flint, and agate: used usually in the form of its prepared white powder chiefly in the manufacture of glass, water glass, ceramics, and abrasives. Also called silicon dioxide.[1795-1805; < NL, deriv. of L silex SILEX]
* * *also called Silicon Dioxide,compound of the two most abundant elements in the Earth's crust, silicon and oxygen, SiO2. The mass of the Earth's crust is 59 percent silica, the main constituent of more than 95 percent of the known rocks. Silica has three main crystalline varieties: quartz (by far the most abundant), tridymite, and cristobalite. Other varieties include coesite, keatite, and lechatelierite. Silica sand is used in buildings and roads in the form of portland cement, concrete, and mortar, as well as sandstone. Silica also is used in grinding and polishing glass and stone; in foundry molds; in the manufacture of glass, ceramics, silicon carbide, ferrosilicon, and silicones; as a refractory material; and as gemstones.
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