metamorphic
Rounded greenstone (likely serpentinite or chlorite-rich metamorphic rock)
Serpentinite/chlorite-actinolite schist; composition commonly dominated by serpentine-group minerals, chlorite, actinolite, magnetite, and minor iron oxides
AI-generated identification · may be incorrectDark olive-green to yellow-brown, mottled, fine-grained, and weakly silky to waxy; approximate Mohs hardness 2.5–5.5 depending on mineral mix, with no obvious cleavage and variable specific gravity around 2.6–3.3. The rounded, glossy surface is naturally water-worn or weathered.
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Physical properties
Dark olive-green to yellow-brown, mottled, fine-grained, and weakly silky to waxy; approximate Mohs hardness 2.5–5.5 depending on mineral mix, with no obvious cleavage and variable specific gravity around 2.6–3.3. The rounded, glossy surface is naturally water-worn or weathered.
Formation & geological history
Typically forms when ultramafic mantle rocks undergo hydration and metamorphism, commonly in ancient oceanic crust and subduction-zone complexes; the pebble’s exact geological age cannot be determined from the image. Its smooth shape indicates shoreline or stream transport.
Uses & applications
Used locally as decorative stone, carvings, lapidary material, and aggregate; attractive pieces may be polished, though this specimen is not gem-grade.
Geological facts
Greenstone is a field term rather than one precise mineral; yellow-brown patches may be iron-oxide weathering, while dark flecks can be magnetite.
Field identification & locations
Look for green mottling, waxy or silky surfaces, very fine grain, and possible weak magnetism; a streak, hardness, acid, and thin-section tests would distinguish serpentinite from chlorite-rich schist. Common in ophiolites and metamorphic belts worldwide.
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