metamorphic
Weathered greenstone pebble
Metamorphosed mafic rock, commonly metabasalt or greenschist (exact identification requires testing)
AI-generated identification · may be incorrectDense, fine-grained, rounded, dull green-gray surface with dark veins or fractures; typically Mohs 5–7, nonmetallic luster, and no visible cleavage. Green color commonly comes from chlorite, epidote, actinolite, or serpentine.
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Physical properties
Dense, fine-grained, rounded, dull green-gray surface with dark veins or fractures; typically Mohs 5–7, nonmetallic luster, and no visible cleavage. Green color commonly comes from chlorite, epidote, actinolite, or serpentine.
Formation & geological history
Likely formed when basaltic volcanic rock was altered by low- to medium-grade metamorphism, often during regional tectonic burial; age depends on its source terrain. Stream or soil transport rounded the specimen and weathering produced its muted surface.
Uses & applications
Common greenstone is used as aggregate, landscaping stone, and occasionally carved ornamental material; attractive pieces may be collected but are generally not gem-grade.
Geological facts
“Greenstone” is a field term covering several rocks, not one mineral. A fresh broken surface, streak, magnetism, acid reaction, and hardness testing are needed to distinguish metabasalt, serpentinite, epidote-rich rock, or other possibilities.
Field identification & locations
Common in regions with ancient volcanic and metamorphic belts, including the Appalachian, Pacific Northwest, and many ophiolite zones. Collector value is usually $1–$10 for a hand specimen, potentially $20–$50 if unusually attractive or compositionally distinctive.
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