metamorphic
Serpentinite (likely serpentinized ultramafic rock)
Serpentinite; chiefly serpentine-group minerals (antigorite, lizardite, chrysotile), with possible magnetite, olivine, pyroxene, and talc
AI-generated identification · may be incorrectDark green-black, mottled and locally rusty orange; commonly waxy to greasy luster, fine-grained, and massive, with Mohs hardness about 2.5–4 and no prominent cleavage. The specimen appears weathered and mixed with lighter quartz/feldspar-bearing material, so exact identification is uncertain from the image alone.
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Physical properties
Dark green-black, mottled and locally rusty orange; commonly waxy to greasy luster, fine-grained, and massive, with Mohs hardness about 2.5–4 and no prominent cleavage. The specimen appears weathered and mixed with lighter quartz/feldspar-bearing material, so exact identification is uncertain from the image alone.
Formation & geological history
Forms when mantle-derived peridotite is hydrated and metamorphosed by water, commonly along faults and mid-ocean ridges; many exposures range from Paleozoic to Mesozoic or younger. Orange-brown surfaces reflect oxidation of iron-bearing minerals.
Uses & applications
Used as decorative stone, sculpture, aggregate, and historically as a source of asbestos where chrysotile is present; it is generally unsuitable for casual cutting or dust production without testing.
Geological facts
Serpentinite often has a distinctive slick, waxy appearance and may be weakly magnetic from magnetite. Some varieties contain chromium, nickel, and asbestos minerals.
Field identification & locations
Look for green-black color, greasy/waxy texture, soft scratch response, and possible magnetism; acid testing is usually negative. Common in California, the Appalachians, the Alps, New Zealand, and ophiolite belts worldwide.
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