metamorphic
Polished greenstone/serpentine pebble (probable)
Serpentinite, dominated by serpentine-group minerals (lizardite/chrysotile); possible accessory olivine or chlorite
AI-generated identification · may be incorrectDark olive-green to black, mottled and faintly translucent in spots, with a waxy to subvitreous luster and irregular granular texture. Hardness is typically 2.5–4 Mohs; cleavage is poor or absent, and specific gravity is about 2.5–2.6.
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Physical properties
Dark olive-green to black, mottled and faintly translucent in spots, with a waxy to subvitreous luster and irregular granular texture. Hardness is typically 2.5–4 Mohs; cleavage is poor or absent, and specific gravity is about 2.5–2.6.
Formation & geological history
Formed when ultramafic mantle rocks such as peridotite were hydrated and metamorphosed during tectonic activity, commonly in ancient oceanic lithosphere and subduction zones. The specimen appears tumbled or naturally water-worn rather than freshly fractured.
Uses & applications
Used as a decorative stone, carving material, ornamental tile, and lapidary material; attractive pieces may be made into cabochons or beads.
Geological facts
Serpentinite commonly contains magnetite, producing dark specks and occasional magnetic response. Chrysotile-bearing material should not be cut, drilled, or powdered because its fibers can be hazardous if inhaled.
Field identification & locations
Look for a greasy or waxy feel, olive-green mottling, low hardness, and possible magnetism; a steel nail may scratch it. Common sources include California, Italy, New Zealand, Canada, and oceanic serpentinite belts, but exact identification requires testing.
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