metamorphic
Polished serpentine-rich rock
Serpentinite, chiefly serpentine-group minerals (Mg₃Si₂O₅(OH)₄), possibly with magnetite and iron-rich alteration minerals
AI-generated identification · may be incorrectDark green, brown, and yellow mottling with waxy to subvitreous luster; typically massive and nonfoliated. Serpentine has Mohs hardness 2.5–4 and specific gravity about 2.5–2.6; the rounded surface is polished, limiting visual identification.
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Physical properties
Dark green, brown, and yellow mottling with waxy to subvitreous luster; typically massive and nonfoliated. Serpentine has Mohs hardness 2.5–4 and specific gravity about 2.5–2.6; the rounded surface is polished, limiting visual identification.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite hydrate during low-temperature metamorphism, commonly along tectonic plate boundaries and subduction zones. Exact age cannot be determined from the photograph.
Uses & applications
Used as decorative stone, carvings, cabochons, and occasionally architectural material; this small polished piece has modest collector value.
Geological facts
Yellow-brown areas may be iron-rich serpentine or weathered inclusions, while black specks can be magnetite or chromite. Serpentinite is California’s state rock.
Field identification & locations
Look for a green waxy appearance, low hardness, curved or splintery fracture, and association with ultramafic rocks; a steel knife may scratch it. Common localities include California, Italy, New Zealand, Canada, and Zimbabwe.
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