metamorphic
Greenstone (likely altered mafic rock)
Chlorite- and amphibole-bearing metabasalt; exact identification requires testing
AI-generated identification · may be incorrectDark green-gray, dull to slightly waxy surface with pale mineral patches; likely fine-grained and tough. Hardness and specific gravity cannot be determined reliably from the photo; greenstone commonly has Mohs hardness about 5–6.
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Physical properties
Dark green-gray, dull to slightly waxy surface with pale mineral patches; likely fine-grained and tough. Hardness and specific gravity cannot be determined reliably from the photo; greenstone commonly has Mohs hardness about 5–6.
Formation & geological history
Formed when basalt or other mafic igneous rock was altered by low-grade metamorphism and hydrothermal fluids. Its age depends on its source locality and cannot be inferred from the image.
Uses & applications
Commonly used as crushed aggregate or dimension stone; attractive pieces may be collected or fashioned into beads and carvings.
Geological facts
The name “greenstone” describes color and alteration, not one unique mineral or rock composition.
Field identification & locations
Look for a dense, dark green rock with fine texture and scattered lighter veins or grains; chlorite, epidote, and amphibole are common. Similar-looking rocks occur worldwide, so a fresh surface and mineral tests are needed for a firm identification.
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