metamorphic
Greenschist
Greenschist (Chlorite-Epidote-Actinolite Schist)
Hardness: 3.5-4.5 on Mohs scale; Color: Dull green, grayish-green, to bright green; Luster: Dull to silky or pearly on foliation planes; Structure: Schistose (layered/foliated); Cleavage: Perfect in one direction due to micaceous minerals.
- Hardness
- 3
- Color
- Dull green, grayish-green, to bright green
- Luster
- Dull to silky or pearly on foliation planes
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Physical properties
Hardness: 3.5-4.5 on Mohs scale; Color: Dull green, grayish-green, to bright green; Luster: Dull to silky or pearly on foliation planes; Structure: Schistose (layered/foliated); Cleavage: Perfect in one direction due to micaceous minerals.
Formation & geological history
Formed by low-grade regional metamorphism of mafic igneous rocks (like basalt or gabbro) or tuff. This process typically occurs at temperatures of 300 to 450 degrees Celsius and depths of 4 to 10 kilometers.
Uses & applications
Used historically as building stone and for carving. Sometimes used in crushed form for road construction or landscaping. Collectors prize specimens with high chlorite or actinolite content for their distinct color and texture.
Geological facts
The color comes primarily from green minerals like chlorite, epidote, and actinolite. It represents the 'greenschist facies' in metamorphic petrology, a specific range of pressure and temperature conditions during mountain building.
Field identification & locations
Identify by its characteristic green hue and platy, foliated texture that allows it to split easily. It feels slightly greasy or soapy if high in chlorite. Commonly found in orogenic belts like the Appalachian Mountains or the Alps.
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