metamorphic
Greenstone (likely altered basalt)
Chlorite- and/or epidote-altered mafic volcanic rock; exact identification needs close examination
AI-generated identification · may be incorrectGreen-gray, fine-grained, dull to slightly waxy surface; likely dominated by altered plagioclase and pyroxene with chlorite, epidote, or actinolite. Hardness and cleavage vary with mineral makeup; the photo does not allow reliable measurement.
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Physical properties
Green-gray, fine-grained, dull to slightly waxy surface; likely dominated by altered plagioclase and pyroxene with chlorite, epidote, or actinolite. Hardness and cleavage vary with mineral makeup; the photo does not allow reliable measurement.
Formation & geological history
Often forms when basalt is metamorphosed or hydrothermally altered, commonly in ancient oceanic crust and greenstone belts; its age cannot be determined from appearance.
Uses & applications
Greenstone is used as crushed aggregate and occasionally as ornamental or carving stone; this small piece has mainly curiosity or collecting value.
Geological facts
The green color typically comes from secondary minerals formed as hot fluids or metamorphism alter iron- and magnesium-rich volcanic rock.
Field identification & locations
A compact, fine-grained green rock with mottled color supports a greenstone identification, but visual appearance alone cannot confirm it. Greenstones occur in metamorphic belts worldwide, including ancient shield regions.
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