metamorphic
Greenschist (Greenstone)
Greenschist (Metamorphic rock containing chlorite, actinolite, and epidote)
Hardness: 3.5-5 (Mohs); Color: Pale green to forest green with dark streaks; Luster: Pearly to dull; Structure: Schistose (layered/foliated); Cleavage: Perfect in one direction due to micaceous minerals; Specific Gravity: 2.8-3.0.
- Hardness
- 3
- Color
- Pale green to forest green with dark streaks
- Luster
- Pearly to dull
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Physical properties
Hardness: 3.5-5 (Mohs); Color: Pale green to forest green with dark streaks; Luster: Pearly to dull; Structure: Schistose (layered/foliated); Cleavage: Perfect in one direction due to micaceous minerals; Specific Gravity: 2.8-3.0.
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks (like basalt) at low temperatures (200-450°C) and moderate pressures. Commonly associated with mountain-building events (orogenies).
Uses & applications
Used as decorative stone, construction aggregate, and occasionally in carving or jewelry if the texture is fine-grained. Historically used for making stone tools.
Geological facts
The 'green' in greenschist comes from the presence of minerals like chlorite, epidote, and actinolite. It represents a specific 'facies' or set of conditions in metamorphic geology.
Field identification & locations
Identify in the field by its distinct green hue and foliated (layered) texture that may cause it to split into thin sheets. Often found in riverbeds or coastal areas near metamorphic belts like the Appalachians or the Alps.
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