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, an abundant group of rock-forming minerals which constitute 60% of the earth's crust. Chemically the feldspars are silicates of aluminum, containing sodium, potassium, iron, calcium, or barium or combinations of these elements.
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a mineral of the feldspar group. It is a triclinic K-Na feldspar with the chemical composition (K, NaXAlSiaOg]; it contains negligible quantities of Ca, Ba, Fe, Rb, and Cs. Microcline often forms perthites, which are microclines with small albite intergrowths. It occurs as individual grains, grain aggregates, prismatic crystals, or single crystals with a volume up to several m3. The mineral has a hardness of 6–6.5 on Mohs’ scale and a density of 2,540–2,570 kg/m3. It may be pink, brownish yellow, reddish white, or pinkish red; less frequently it is white or bluish green (amazonite, or amazonstone). Microcline has a vitreous or pearly luster. A thin section of the mineral under the microscope shows multiple twins, forming the characteristic microclinic grating structure.
Microcline is a typical rock-forming mineral contained in granite, granodiorite (syenite), pegmatite, and gneiss. It is the primary raw material used by the ceramics industry (porcelain, glazed pottery, and industrial ceramics). Amazonite is used as an ornamental stone.