Silicate

In chemistry, a silicate is any member of a family of anions consisting of silicon and oxygen, usually with the general formula n, where 0 ≤ x < 2. The family includes orthosilicate SiO4−4 (x = 0), metasilicate SiO2−3 (x = 1), and pyrosilicate Si2O6−7 (x = 0.5, n = 2). The name is also used for any salt of such anions, such as sodium metasilicate; or any ester containing the corresponding chemical group, such as tetramethyl orthosilicate. In chemistry, a silicate is any member of a family of anions consisting of silicon and oxygen, usually with the general formula n, where 0 ≤ x < 2. The family includes orthosilicate SiO4−4 (x = 0), metasilicate SiO2−3 (x = 1), and pyrosilicate Si2O6−7 (x = 0.5, n = 2). The name is also used for any salt of such anions, such as sodium metasilicate; or any ester containing the corresponding chemical group, such as tetramethyl orthosilicate. Silicate anions are often large polymeric molecules with an extense variety of structures, including chains and rings (as in polymeric metasilicate n), double chains (as in n, and sheets (as in n. In geology and astronomy, the term silicate is used to mean silicate minerals, ionic solids with silicate anions; as well as rock types that consist predominantly of such minerals. In that context, the term also includes the non-ionic compound silicon dioxide SiO2 (silica, quartz), which would correspond to x = 2 in the general formula. The term also includes minerals where aluminum or other tetravalent atoms replace some of the silicon atoms, as in the aluminosilicates. Such silicates comprise most of Earth's crust and mantle, as well as the other terrestrial planets, rocky moons, and asteroids. Silicates are extremely important materials, both natural (such as granite, gravel, and garnet) and artificial (such as Portland cement, ceramics, glass, and waterglass), for all sorts of technological and artistic activities. The name 'silicate' is sometimes extended to any anions containing silicon, even if they do not fit the general formula or contain other atoms besides oxygen; such as the hexahydroxysilicate 2− or hexafluorosilicate 2−. In most commonly encountered silicates, including almost all silicate minerals found in the Earth's crust, each silicon atom occupies the center of an idealized whose corners are four oxygen atoms, connected to it by single covalent bonds according to the octet rule. These tetrahedra may occur as isolated orthosilicate anions SiO4−4, but two or more silicon atoms can be joined with oxygen atoms in various ways, to form more complex anions, such as pyrosilicate Si2O6−7 or the metasilicate ring hexamer Si6O12−18. Polymeric silicate anions of arbitrarily large sizes can have chain, double chain, sheet, or three-dimensional structures.