metamorphic
Greenstone / serpentinized ultramafic rock
Serpentinite, chiefly serpentine-group minerals (chrysotile, lizardite, antigorite), commonly with magnetite and minor chlorite or pyroxene
AI-generated identification · may be incorrectTypically dark green to black, waxy to dull luster, massive and fine-grained, with Mohs hardness about 2.5–4 and specific gravity roughly 2.5–2.7; weak cleavage and irregular fracture. The rounded, weathered specimen may also contain iron-rich alteration or chlorite, making exact identification uncertain without testin…
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Physical properties
Typically dark green to black, waxy to dull luster, massive and fine-grained, with Mohs hardness about 2.5–4 and specific gravity roughly 2.5–2.7; weak cleavage and irregular fracture. The rounded, weathered specimen may also contain iron-rich alteration or chlorite, making exact identification uncertain without testing.
Formation & geological history
Forms when mantle-derived peridotite is hydrated and metamorphosed by fluids, commonly along tectonic plate boundaries and fault zones. Serpentinization is mostly Phanerozoic in exposed examples, though the process occurs throughout geologic time.
Uses & applications
Used as decorative stone, carvings, countertops, and historically as a source rock for asbestos-bearing serpentine; attractive pieces are collected, but fibrous material should not be cut or powdered.
Geological facts
Commonly associated with ophiolites and chromite deposits. A streak, hardness, magnetism, and thin-section or X-ray testing would distinguish serpentinite from jade, chlorite-rich greenstone, or copper-stained rock.
Field identification & locations
Look for greasy or waxy green surfaces, a relatively soft texture, dark veins, and occasional magnetism from magnetite. Common localities include California, Vermont, Italy, New Zealand, and ophiolite belts worldwide.
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