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The mineral hornblende is a complex silicate which is an isomorphous mixture of three molecules; a calcium-iron-magnesium silicate, an aluminium-iron-magnesium silicate, and an iron-magnesium silicate. Manganese, titanium, and alkalis are sometimes present. Hornblende has a hardness of 5-6, a specific gravity of 2.9-3.4, and is colored green, greenish-brown, opaque, brown and black.

Hornblende is a common constituent of many igneous rocks such as granite, syenite, diorite or gabbro, of gneisses and schists, and is the principal mineral of amphibolites. Hornblende alters easily to chlorite and epidote. A variety of hornblende that contains less than 5% of iron oxides is gray to white in color and named edenite, from its locality in Edenville, New York. Very dark brown to black hornblendes which contain titanium ordinarily are called basaltic hornblende from the fact that they are usually a constituent of basalt and related rocks.

The word hornblende is derived from the German horn and blende, to blind or dazzle. The term blende was often used to refer to a brilliant non-metallic lustre, for example, zincblende, and pitchblende, a lustrous form of uraninite.

See also: List of minerals