metamorphic
Likely greenstone (altered basalt)
Chlorite–actinolite-bearing metabasalt; identification is tentative from the image
AI-generated identification · may be incorrectDark olive-green, fine-grained and rough, with a pale mineral patch; likely dominated by chlorite and amphibole, with possible epidote or feldspar. Hardness and luster cannot be reliably determined visually; greenstone commonly has Mohs hardness around 5–6 and a dull to slightly silky luster.
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Physical properties
Dark olive-green, fine-grained and rough, with a pale mineral patch; likely dominated by chlorite and amphibole, with possible epidote or feldspar. Hardness and luster cannot be reliably determined visually; greenstone commonly has Mohs hardness around 5–6 and a dull to slightly silky luster.
Formation & geological history
Forms when basalt is altered by low-grade metamorphism and hydrothermal fluids, commonly in ancient oceanic crust and volcanic belts. Its age cannot be determined from the photograph.
Uses & applications
Greenstone is used as aggregate and building stone; attractive, sound pieces may be cut for ornamental objects or collected.
Geological facts
“Greenstone” describes a green-colored altered rock, not one unique mineral or fixed composition.
Field identification & locations
Look for a dense, fine-grained texture and green minerals; a hand lens and hardness or streak tests can help distinguish it from other green rocks. Greenstones occur in metamorphic belts worldwide.
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mineral