metamorphic
Greenschist
Greenschist (composed primarily of Chlorite, Actinolite, and Epidote)
Hardness: 3.5-4.5 (Mohs); Color: Pale to dark green with brownish weathering; Luster: Dull to silky; Structure: Foliated (schistose texture); Cleavage: Perfect schistosity (splits into thin, rough sheets)
- Hardness
- 3
- Color
- Pale to dark green with brownish weathering
- Luster
- Dull to silky
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Physical properties
Hardness: 3.5-4.5 (Mohs); Color: Pale to dark green with brownish weathering; Luster: Dull to silky; Structure: Foliated (schistose texture); Cleavage: Perfect schistosity (splits into thin, rough sheets)
Formation & geological history
Formed through regional metamorphism of mafic igneous rocks (like basalt) under low-temperature and medium-pressure conditions (Greenschist facies). Most specimens date from the Paleozoic to Precambrian eras depending on location.
Uses & applications
Used primarily in construction as crushed stone or landscaping rock. Occasionally used as flagging or building stone; historically used for primitive tools or carvings due to softness compared to granite.
Geological facts
Greenschist is a definitive indicator of the 'greenschist facies' in geology, marking a specific range of pressure and temperature during mountain building. The green color is derived directly from the presence of chlorite and epidote.
Field identification & locations
Identify in the field by its distinct greenish hue, platy texture that is rougher than slate, and tendency to crumble or flake into greenish-gray dust. Commonly found in eroded mountain belts like the Appalachians or the Alps.
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