metamorphic
Greenstone / Epidosite
Metamorphosed Mafic Igneous Rock (Epidote-Chlorite group)
Hardness: 6-7 (Mohs scale), Color: Dull to pistachio green, Luster: Vitreous to waxy (when wet/polished), Structure: Massive or foliated fine-grained texture, Cleavage: Poor
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Dull to pistachio green, Luster: Vitreous to waxy (when wet/polished), Structure: Massive or foliated fine-grained texture, Cleavage: Poor
Formation & geological history
Formed through low-grade regional metamorphism of basaltic or gabbroic rocks, specifically during the greenschist facies process where minerals like pyroxene are replaced by epidote and chlorite.
Uses & applications
Used primarily as decorative gravel, construction aggregate, and occasionally in lapidary work for cabochons or tumbled stones.
Geological facts
Greenstone is a broad term for any compact dark-green altered or metamorphosed basic igneous rock. The green color is primarily due to the presence of chlorite, actinolite, or epidote minerals.
Field identification & locations
Identify by its distinct olive-to-pistachio green hue and hardness; it cannot be scratched by a steel pocket knife. Commonly found in ancient mountain belts and coastal pebble beaches.
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