metamorphic
Greenstone, likely altered basalt
Metabasalt (chlorite–actinolite–epidote assemblage), likely greenschist-facies greenstone
AI-generated identification · may be incorrectFine-grained, dull green to gray-green, massive and weakly foliated with a rough texture; typical hardness is about 5–6 Mohs, with no obvious cleavage and a granular/interlocking crystal structure. Green color commonly comes from chlorite, actinolite, epidote, and altered pyroxene.
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Physical properties
Fine-grained, dull green to gray-green, massive and weakly foliated with a rough texture; typical hardness is about 5–6 Mohs, with no obvious cleavage and a granular/interlocking crystal structure. Green color commonly comes from chlorite, actinolite, epidote, and altered pyroxene.
Formation & geological history
Formed when basaltic lava was metamorphosed by low- to medium-grade heat and pressure, commonly during mountain building or oceanic-crust alteration. Its exact age cannot be determined from the photograph; greenstone occurs from Precambrian to modern tectonic belts.
Uses & applications
Used locally as crushed aggregate, road stone, landscaping rock, and historically for tools or ceremonial objects; attractive polished pieces are collectible but are generally not jewelry-grade.
Geological facts
“Greenstone” is a field term rather than one precise mineral or rock species, and appearance alone cannot distinguish metabasalt from altered volcanic rock or serpentinite.
Field identification & locations
Look for a dark green, fine-grained, heavy rock that is harder than most sedimentary rocks; a streak test, magnetism, acid reaction, and thin-section or XRF analysis improve identification. Common settings include ancient volcanic belts and metamorphic terrains worldwide.
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