silicate

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silicates The most important and abundant group of rock-forming minerals, which can be classified according to the structural arrangement of the fundamental SiO4 tetrahedra which are the main building blocks of the group. (a) Nesosilicates have independent SiO4 tetrahedra linked by cations, e.g. olivine group, (b) Sorosilicates have two SiO4 tetrahedra sharing one oxygen, e.g. epidote group. (c) Cyclosilicates have rings of three, four, or six linked SiO4 tetrahedra, e.g. axinite and tourmaline. (d) Inosilicates (chain silicates) have SiO4 tetrahedra linked either into single chains by sharing two oxygens, e.g. pyroxene group, or into double chains (band silicates) by alternately sharing two or three oxygens, e.g. amphibole group, (e) Phyllosilicates (sheet silicates) share three oxygens to form a flat sheet, e.g. mica group. (f) Tectosilicates have SiO4 tetrahedra linked into a three-dimensional framework by sharing all the oxygens, e.g. feldspar and quartz groups.

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silicate, chemical compound containing silicon, oxygen, and one or more metals, e.g., aluminum, barium, beryllium, calcium, iron, magnesium, manganese, potassium, sodium, or zirconium. Silicates may be considered chemically as salts of the various silicic acids. For a long time classified as ortho-, meta-, di-, or trisilicates according to the acid from which they are (theoretically) derived, they are now also classified by an X-ray diffraction method according to their crystalline structure. Silicates are widely distributed in nature, making up most of the earth's outer crust and mantle; bridgmanite, the most common mineral on earth, comprising 70% of the lower mantle, is high-density magnesium iron silicate. Most of the common rock-forming minerals (e.g., quartz, feldspar, mica, and pyroxene) are silicates, as are asbestos, beryl, aquamarine, emerald, serpentine, and talc. Clay consists essentially of hydrous aluminum silicates mixed with other substances. Glass is a mixture of silicates, as is water glass. See sodium silicate.

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sil·i·cate / ˈsiləˌkāt; -kit/ • n. Chem. a salt in which the anion contains both silicon and oxygen, esp. one of the anion SiO42−. ∎  any of the many minerals consisting primarily of SiO42− combined with metal ions, forming a major component of the rocks of the earth's crust.