metamorphic
Greenstone (likely chlorite- or actinolite-rich metabasalt)
Metamorphosed mafic volcanic rock; commonly greenschist-facies basalt, composed chiefly of chlorite, actinolite, epidote, and albite
AI-generated identification · may be incorrectDark green-gray, fine-grained and dull, with a rough, uneven surface and possible foliation; hardness and density vary with mineral content. The photo does not show enough detail for a definitive mineral or crystal-structure identification.
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Physical properties
Dark green-gray, fine-grained and dull, with a rough, uneven surface and possible foliation; hardness and density vary with mineral content. The photo does not show enough detail for a definitive mineral or crystal-structure identification.
Formation & geological history
Typically forms when basalt or similar mafic rock is altered by low-grade regional metamorphism and hydrothermal fluids. Its age and specific formation environment cannot be determined from the image.
Uses & applications
Used locally as building or landscaping stone and collected as a geological specimen; this piece appears unworked beyond natural weathering or breakage.
Geological facts
“Greenstone” is a descriptive field term rather than a single precise rock composition; its green color commonly comes from chlorite, actinolite, or epidote.
Field identification & locations
Look for a dense, dark-green rock with fine grains and, in some specimens, weak foliation; confirm with a fresh surface and mineral tests. Greenstone belts occur worldwide, but locality cannot be inferred from this image.
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