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[Si7AlO22](OH,F)2, and pargasite NaCa2(Mg4Al)[Si6Al2O22](OH,F)2; sp. gr. 3.0–3.5; hardness 5.0–6.0; black or greenish-black; white streak with a greenish tint; vitreous lustre; crystals normally prismatic, columnar, and occasionally isometric; cleavages in two directions set at 124°, 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).