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the name given to igneous rocks that have undergone regional metamorphism at low temperatures and whose color is determined by the high content of green minerals (chlorite, amphibole) formed out of primary magmatic minerals and glass. Mainly volcanic and, less often intrusive rocks that are basic, intermediate, and sometimes acid (rhyolite) in composition and that are formed in folded regions are altered into greenstone. In regions where greenstone is wide-spread, such as the Urals and the state of Nevada in the USA, it serves as an indicator of pyrite deposits.
REFERENCESWinkler, H. Genezis metamorficheskikh porod. Moscow, 1969. (Translated from German.)
Marakushev, A. A.Problemy mineral’nykhfatsii metamorficheskikh i metasomaticheskikh gornykh porod. Moscow, 1965.