greenschist facies

Greenschist - also known as greenstone - is a general field petrologic term applied to metamorphic and/or altered mafic volcanic rock. The green is due to abundant green chlorite, actinolite and epidote minerals that dominate the rock. However, basalts may remain quite black if primary pyroxene does not revert to chlorite or actinolite. To qualify for the name a rock must also exhibit schistocity or some foliation or layering. An alternate term for these rocks is greenstone. The rock is derived from basalt, gabbro or similar rocks containing sodium-rich plagioclase feldspar, chlorite, epidote and quartz. Chlorite and epidote give the green colour [1].
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B: (Kimia) fasies greenschist
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