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Greenstone: Greenstone is a non-foliated metamorphic rock derived from basalt or chemically equivalent rock such as gabbro. Greenstones contain sodium-rich plagioclase feldspar, chlorite, and epidote, as well as quartz. The chlorite and epidote make greenstones green. Greenschist: A grade of metamorphism characterized by abundant chlorite and schistosity. Greenschist "facies" metamorphic rocks are produced under relatively low temperature-pressure conditions. -- Excerpts from: USGS/NPS Geology in the Parks Website, 2001, and Geology in Michigan Glossary, State of Michigan website, 2003 |