metamorphic
Greenstone (likely altered basalt)
Chlorite- and epidote-altered mafic volcanic rock; commonly called greenschist or greenstone
AI-generated identification · may be incorrectFine-grained, pale green-gray specimen with dark fractures and a dull to weakly silky luster. Hardness and cleavage vary with its minerals; chlorite is about 2–2.5 Mohs and epidote 6–7. The image alone does not establish its exact composition.
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Physical properties
Fine-grained, pale green-gray specimen with dark fractures and a dull to weakly silky luster. Hardness and cleavage vary with its minerals; chlorite is about 2–2.5 Mohs and epidote 6–7. The image alone does not establish its exact composition.
Formation & geological history
Typically formed when basalt or related mafic rock was altered by low-grade metamorphism and hydrothermal fluids, often during ancient seafloor alteration or mountain-building. Greenstones occur in geological belts ranging from Archean to much younger ages.
Uses & applications
Greenstone is used as crushed aggregate, dimension stone, and occasionally for carved objects or jewelry; this small rough fragment has mainly educational or collecting interest.
Geological facts
Its green color commonly comes from chlorite, epidote, or actinolite replacing minerals in the original volcanic rock.
Field identification & locations
Look for a dense, fine-grained green rock, often with veins or patches and association with other altered volcanic rocks. It is common in metamorphic belts worldwide; confirming the identification requires closer examination or testing.
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