metamorphic
Probable serpentinite (serpentine-rich rock)
Serpentinite; chiefly serpentine-group minerals (Mg₃Si₂O₅(OH)₄), with possible magnetite and olivine remnants
AI-generated identification · may be incorrectDark green-gray, mottled, waxy to slightly greasy luster, irregular fracture, and fine-grained massive texture; Mohs hardness about 2.5–4, with variable density and no consistent cleavage. The small specimen appears rough and naturally fractured, though exact identification requires testing.
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Physical properties
Dark green-gray, mottled, waxy to slightly greasy luster, irregular fracture, and fine-grained massive texture; Mohs hardness about 2.5–4, with variable density and no consistent cleavage. The small specimen appears rough and naturally fractured, though exact identification requires testing.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite are hydrated during low-temperature metamorphism, commonly along tectonic plate boundaries and fault zones. Serpentinization is generally younger than the original mantle rock and may occur from Precambrian to modern times.
Uses & applications
Used as decorative and architectural stone, carving material, aggregate, and historically as a source of magnesium and asbestos-bearing minerals; attractive pieces are collected.
Geological facts
Often contains magnetite, making some specimens weakly magnetic. Fibrous chrysotile may occur, so avoid grinding or creating dust.
Field identification & locations
Common in ophiolites and ultramafic belts, including California, Italy, New Zealand, and parts of Canada. A waxy green appearance, low hardness, and possible magnetism help distinguish it from ordinary basalt; acid testing is usually ineffective.
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