metamorphic
Greenstone / Greenschist
Greenschist (composed of Chlorite, Epidote, Actinolite)
Hardness: 3.5 to 5 on Mohs scale (depends on mineral concentration); Color: Dull to sage green; Luster: Dull to waxy; Texture: Fine-grained, often smooth from water erosion; Cleavage: Good to poor depending on schistosity.
- Hardness
- 3
- Color
- Dull to sage green
- Luster
- Dull to waxy
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Physical properties
Hardness: 3.5 to 5 on Mohs scale (depends on mineral concentration); Color: Dull to sage green; Luster: Dull to waxy; Texture: Fine-grained, often smooth from water erosion; Cleavage: Good to poor depending on schistosity.
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks (like basalt) at low temperatures and pressures. This color is typically indicative of the presence of chlorite and epidote minerals.
Uses & applications
Historically used for stone tools/axes; currently used for decorative garden stones, aquarium gravel, and occasionally for folk jewelry or as river pebbles.
Geological facts
The term greenstone is often used loosely for any hard, green altered igneous rock. It is a major component of 'Greenstone Belts' which are geological formations that contain some of the oldest rocks on Earth.
Field identification & locations
Identify in the field by its distinct green hue and soapy or waxy feel if chlorite is high. Commonly found in riverbeds or coastal areas where ancient metamorphic belts meet the water.
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