metamorphic
Weathered greenstone
Metamorphosed mafic rock, commonly chlorite–actinolite schist or altered basalt
AI-generated identification · may be incorrectTypically dark green to gray-green, dull to weakly silky, fine- to medium-grained, and irregularly fractured; hardness about 5–6 Mohs. The reddish patches may be iron-oxide weathering, while pale green areas commonly contain chlorite, epidote, or actinolite.
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Physical properties
Typically dark green to gray-green, dull to weakly silky, fine- to medium-grained, and irregularly fractured; hardness about 5–6 Mohs. The reddish patches may be iron-oxide weathering, while pale green areas commonly contain chlorite, epidote, or actinolite.
Formation & geological history
Formed when basalt or gabbro underwent low- to moderate-grade metamorphism and hydrothermal alteration, commonly during ancient oceanic or mountain-building events. Exact age cannot be determined from the photograph.
Uses & applications
Used locally as crushed aggregate, landscaping stone, and occasionally as a decorative lapidary material; this weathered specimen has little jewelry value.
Geological facts
Its green color usually reflects alteration of iron- and magnesium-rich minerals rather than a single mineral. The cavities and rough surface likely result from weathering, dissolved veins, or formerly gas-filled spaces.
Field identification & locations
Look for a green, dense rock with black amphibole or chlorite, epidote-like grains, and no obvious sedimentary layering; a streak, hardness, and acid test can help distinguish it from serpentine or green jasper. Common in metamorphic belts and altered volcanic terrains worldwide.
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