metamorphic
Greenstone pebble (likely altered basalt or serpentine)
Greenschist-facies mafic rock; commonly chlorite–actinolite–epidote ± serpentine
AI-generated identification · may be incorrectFine-grained, rounded, dull to weakly silky green surface with darker streaks; typically Mohs 5–6 (serpentine-rich varieties 2.5–4), opaque, poor cleavage, and specific gravity about 2.7–3.3. Exact identification requires testing for hardness, streak, magnetism, and mineral texture.
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Physical properties
Fine-grained, rounded, dull to weakly silky green surface with darker streaks; typically Mohs 5–6 (serpentine-rich varieties 2.5–4), opaque, poor cleavage, and specific gravity about 2.7–3.3. Exact identification requires testing for hardness, streak, magnetism, and mineral texture.
Formation & geological history
Likely a river-worn pebble derived from metamorphosed or hydrothermally altered basalt, formed during regional metamorphism or seafloor alteration; age depends on its source terrain. Weathering and stream transport produced its smooth shape.
Uses & applications
Used locally as decorative stone, landscaping aggregate, or lapidary material; attractive green pieces may be polished, but this specimen appears ordinary and uncut.
Geological facts
“Greenstone” is a field term rather than one precise mineral or rock; similar pebbles may be greenschist, altered basalt, epidote-rich rock, or serpentine.
Field identification & locations
Look for green chlorite/actinolite, fine grain, and a non-glassy surface; a steel file or knife can distinguish softer serpentine from harder greenschist. Common in stream gravels downstream from volcanic or metamorphic terranes.
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