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).

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.

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.