actinolite

Amphibole Am"phi*bole ([a^]m"f[i^]*b[=o]l), n. [Gr. 'amfi`bolos doubtful, equivocal, fr. 'amfiba`llein to throw round, to doubt: cf. F. amphibole. Ha["u]y so named the genus from the great variety of color and composition assumed by the mineral.] (Min.) A common mineral embracing many varieties varying in color and in composition. It occurs in monoclinic crystals; also massive, generally with fibrous or columnar structure. The color varies from white to gray, green, brown, and black. It is a silicate of magnesium and calcium, with usually aluminium and iron. Some common varieties are {tremolite}, {actinolite}, {asbestus}, {edenite}, {hornblende} (the last name being also used as a general term for the whole species). Amphibole is a constituent of many crystalline rocks, as syenite, diorite, most varieties of trachyte, etc. See {Hornblende}. [1913 Webster]