igneous
Greenstone (likely altered basalt)
Metamorphosed mafic volcanic rock, commonly chlorite- and actinolite-rich; exact identification requires testing
AI-generated identification · may be incorrectSmall, rough, dark green to olive fragment with a granular, mottled surface. Hardness and luster cannot be determined reliably from the image; greenstone commonly contains plagioclase, chlorite, actinolite, and epidote.
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Physical properties
Small, rough, dark green to olive fragment with a granular, mottled surface. Hardness and luster cannot be determined reliably from the image; greenstone commonly contains plagioclase, chlorite, actinolite, and epidote.
Formation & geological history
Formed when basaltic lava or shallow intrusions were altered by low-grade metamorphism and hydrothermal fluids. Such rocks occur in ancient greenstone belts spanning much of Earth’s geological history.
Uses & applications
Commonly used as crushed aggregate or building stone; attractive, sound pieces may be polished or used decoratively.
Geological facts
“Greenstone” is a field term for several green, altered mafic rocks rather than one precisely defined mineral or rock species.
Field identification & locations
Look for a dense, fine-grained texture and green minerals; confirm with a fresh surface and mineralogical tests. Found in metamorphic belts worldwide, including Canada, Australia, and southern Africa.
