metamorphic

Greenstone pebble (likely altered basalt or serpentine)

Greenschist-facies mafic rock; commonly chlorite–actinolite–epidote ± serpentine

AI-generated identification · may be incorrect

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.

Identified September 7, 2026More metamorphic →

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Physical properties

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.