One of the major divisions of the mineral facies classification of metamorphic rocks, encompassing rocks that formed under conditions of moderate to high temperatures (950°F, or 500°C, maximum) and pressures. Less-intense temperatures and pressures form rocks of the epidote-amphibolite facies, and more-intense temperatures and pressures form rocks of the granulite facies. Amphibole, diopside, epidote, plagioclase, certain types of garnet, and wollastonite are minerals typically found in amphibolite facies rocks. They are widely distributed in Precambrian gneisses and probably formed in the deeper parts of folded mountain belts.
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Igneous or metamorphic rock composed largely or dominantly of amphibole minerals. For igneous rocks, the term hornblendite is usually used and is more restrictive; hornblende is the most common amphibole. Metamorphic amphibolites are more widespread and variable than igneous ones. Typically, they are medium- to coarse-grained and are composed of hornblende and plagioclase. Basic igneous rocks such as basalts and gabbros (see acid and basic rocks) can be the parent rocks of amphibolite.
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