"Amphibolite ( /æmˈfɪbəlaɪt/) is a metamorphic rock that contains amphibole, especially the species hornblende and actinolite, as well as plagioclase.
Amphibolite is a grouping of rocks composed mainly of amphibole and plagioclase feldspar, with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flaky) structure. The small flakes of black and white in the rock often give it a salt-and-pepper appearance.
Amphibolite need not be derived from metamorphosed mafic rocks. Because metamorphism creates minerals entirely based upon the chemistry of the protolith, certain ´dirty marls´ and volcanic sediments may actually metamorphose to an amphibolite assemblage. Deposits containing dolomite and siderite also readily yield amphibolite (tremolite-schist, grunerite-schist, and others) especially where there has been a certain amount of contact metamorphism by adjacent granitic masses. Metamorphosed basalt creates ortho-amphibolite and other chemically appropriate lithologies create para-amphibolite." - (en.wikipedia.org 29.02.2020)
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