Hornblende - biotite, Castlewellan, Co Down, Ireland. Polarized photomicrograph thin section.
Hornblende is a complex inosilicate series of minerals (ferrohornblende – magnesiohornblende). It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende is an isomorphous mixture of three molecules; a calcium-iron-magnesium silicate, an aluminium-iron-magnesium silicate, and an iron-magnesium silicate. Hornblende is a common constituent of many igneous and metamorphic rocks such as granite, syenite, diorite, gabbro, basalt, andesite, gneiss, and schist. It is the principal mineral of amphibolites. Very dark brown to black hornblendes that contain titanium are ordinarily called basaltic hornblende, from the fact that they are usually a constituent of basalt and related rocks. Hornblende alters easily to chlorite and epidote.
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Photo credit: © Scenics & Science / Alamy / Afripics
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Keywords: -, biotite, castlewellan, diorite, gabbro, geology, hornblende, inosilicate, ireland., isomorphous, microscope, mineralogy, photomicrograph, polarized, section., syenite, thin
