Hornblende

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hornblende An important rock-forming silicate mineral and member of the amphiboles, particularly the calcium-rich monoclinic amphiboles; it is the general name given to a group of amphiboles (the hornblende series) with similar properties, which includes hastingsite Ca2(Mg4Al)[Si7AlO22](OH,F)2, tschermakite Ca2(Mg3AL2)[Si6Al2O22](OH,F)2, edenite NaCa2Mg5 [Si6AlO22] (OH, F)2, and pargasite NaCa2(Mg4Al) [Si6Al2O22](OH,F)2; sp. gr. 3.0–3.5; hardness 5.0–6.0; black or greenishblack; white streak with a greenish tint; vitreous lustre; crystals normally prismatic, columnar, and occasionally isometric; cleavages in two directions set at 1240, prismatic {110}; occurs as a common constituent of medium basic, igneous rocks (e.g. syenites, diorites, and granodiorites), also in contact metasomatic zones, and extensively in metamorphic rocks (e.g. schists, gneisses, and amphibolites).

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hornblende Black or green mineral found in igneous and metamorphic rocks. It is the commonest form of amphibole, and contains iron and silicates of calcium, aluminium and magnesium. Hardness 5.5; r.d. 3.2.

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horn·blende / ˈhôrnˌblend/ • n. a dark brown, black, or green mineral of the amphibole group consisting of a hydroxyl alumino-silicate of calcium, magnesium, and iron, occurring in many igneous and metamorphic rocks.

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hornblende: see amphibole.