metamorphic
Serpentinite
Serpentinite, chiefly serpentine-group minerals (antigorite, lizardite, chrysotile), commonly with magnetite and chromite
AI-generated identification · may be incorrectTypically dark green to black, mottled, waxy to greasy luster, Mohs hardness about 2.5–4; massive and fine-grained with no obvious crystal cleavage. The specimen’s green-black color and subtly fibrous, rough texture are consistent with serpentinite.
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Physical properties
Typically dark green to black, mottled, waxy to greasy luster, Mohs hardness about 2.5–4; massive and fine-grained with no obvious crystal cleavage. The specimen’s green-black color and subtly fibrous, rough texture are consistent with serpentinite.
Formation & geological history
Forms when olivine- and pyroxene-rich ultramafic rocks hydrate during low-temperature metamorphism, often near tectonic plate boundaries; formation ages vary from Precambrian to modern tectonic settings.
Uses & applications
Used as decorative and architectural stone, carvings, aggregate, and historically as a source of asbestos-bearing material; attractive pieces are collected but are generally not jewelry gemstones.
Geological facts
Serpentinite can contain magnetite, making some pieces weakly magnetic, and may weather to form distinctive green soils. Fibrous chrysotile varieties should not be cut, drilled, or inhaled because of asbestos risk.
Field identification & locations
Common in California, Italy, New Zealand, Canada, and ophiolite belts worldwide; identify by green-black color, waxy feel, softness, and possible magnetism. A firm identification requires testing or thin-section analysis.
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