metamorphic
Weathered greenstone (altered mafic rock)
Greenschist-facies metabasalt; typically chlorite, actinolite, epidote, and albite
AI-generated identification · may be incorrectDull, pale green-gray, fine-grained and massive, with rusty weathering spots; constituent minerals are generally Mohs 5–6, but the rock’s hardness varies. The image alone does not establish its exact mineralogy or crystal structure.
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Physical properties
Dull, pale green-gray, fine-grained and massive, with rusty weathering spots; constituent minerals are generally Mohs 5–6, but the rock’s hardness varies. The image alone does not establish its exact mineralogy or crystal structure.
Formation & geological history
Formed when basalt or similar mafic rock was altered by low-grade metamorphism and hydrothermal fluids; its age depends on the source formation and cannot be determined from the photo.
Uses & applications
Commonly used as crushed aggregate or dimension stone; attractive, sound pieces may be collected or cut for decorative use.
Geological facts
“Greenstone” describes a color and alteration, not one uniquely defined rock composition.
Field identification & locations
Look for a dense greenish rock with fine-grained texture and chlorite/epidote alteration; similar rocks occur in ancient volcanic belts worldwide. Confirm identification with mineral or laboratory testing.
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