"Greenschist are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically 300–450 °C (570–840 °F) and 2–10 kilobars (14,500–58,000 psi)."

picture:
http://www.uni-muenster.de/GeoPalaeontologie/Geologie/Endogen/S3.html

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