metamorphic
Serpentinized ultramafic rock (likely serpentinite)
Serpentinite; chiefly serpentine-group minerals Mg₃Si₂O₅(OH)₄, with magnetite, olivine, and pyroxene remnants
AI-generated identification · may be incorrectTypically dark green, black, brown, and mottled cream; waxy to submetallic luster, fine-grained to fibrous texture, Mohs hardness about 2.5–4, and specific gravity roughly 2.5–2.7. The specimen appears massive and strongly veined or brecciated rather than distinctly crystalline.
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Physical properties
Typically dark green, black, brown, and mottled cream; waxy to submetallic luster, fine-grained to fibrous texture, Mohs hardness about 2.5–4, and specific gravity roughly 2.5–2.7. The specimen appears massive and strongly veined or brecciated rather than distinctly crystalline.
Formation & geological history
Forms when mantle-derived peridotite is hydrated and metamorphosed by water, commonly along oceanic crust and tectonic fault zones. Serpentinization ranges from ancient Precambrian occurrences to modern geological settings.
Uses & applications
Used as decorative stone, carvings, countertops, and occasionally aggregate; attractive polished pieces may be sold as ornamental stone, though this rough specimen is unlikely to be gem-grade.
Geological facts
Serpentinite commonly contains magnetite, explaining dark patches and occasional weak magnetism; some varieties may contain asbestos-form serpentine minerals, so avoid cutting or generating dust.
Field identification & locations
Look for green-black mottling, a relatively soft waxy surface, vein-like patterns, and possible magnetism. Common localities include California, Italy, New Zealand, the Alps, and ophiolite belts worldwide.
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