metamorphic
Serpentinized ultramafic rock (likely serpentinite)
Serpentinite; chiefly serpentine-group minerals, Mg₃Si₂O₅(OH)₄, with possible magnetite, olivine, pyroxene, and sulfides
AI-generated identification · may be incorrectDark green-black to yellow-green, mottled and waxy/greasy luster, massive texture, commonly veined; Mohs hardness about 2.5–4, typically low-to-moderate specific gravity, with no obvious cleavage. The metallic-looking patches may be magnetite or sulfide minerals.
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Physical properties
Dark green-black to yellow-green, mottled and waxy/greasy luster, massive texture, commonly veined; Mohs hardness about 2.5–4, typically low-to-moderate specific gravity, with no obvious cleavage. The metallic-looking patches may be magnetite or sulfide minerals.
Formation & geological history
Forms when oceanic peridotite is hydrated and metamorphosed by circulating water, commonly in ophiolite belts and subduction zones. The specimen’s exact geological age cannot be determined from the photograph.
Uses & applications
Used as decorative stone, carvings, countertops, and historically as a source of asbestos-bearing material; attractive pieces are collected, though asbestos content requires caution when cutting or abrading.
Geological facts
Serpentinite often has a characteristic green, mottled appearance and may feel unusually smooth or soapy. It can contain magnetite and may weakly attract a magnet.
Field identification & locations
Common in California, Italy, New Zealand, Canada, and many ophiolite complexes worldwide. Confirm with a hardness test, streak, magnet, and ideally petrographic or X-ray analysis; avoid producing dust until asbestos is excluded.
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