metamorphic
Serpentinite (serpentine-rich metamorphic rock)
Serpentinite; chiefly serpentine-group minerals, Mg₃Si₂O₅(OH)₄, with possible magnetite, chlorite, talc, and pyroxene
AI-generated identification · may be incorrectTypically olive-green, gray, black, or mottled with a waxy to greasy luster; hardness about 2.5–4 Mohs, variable cleavage, and commonly massive or foliated rather than visibly crystalline. The specimen’s green-black, uneven surface is consistent with serpentinite, though image-only identification is not definitive.
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Physical properties
Typically olive-green, gray, black, or mottled with a waxy to greasy luster; hardness about 2.5–4 Mohs, variable cleavage, and commonly massive or foliated rather than visibly crystalline. The specimen’s green-black, uneven surface is consistent with serpentinite, though image-only identification is not definitive.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite are hydrothermally altered by water, commonly along oceanic crust, subduction zones, and tectonic faults. Formation ages range from Precambrian to recent geological episodes, depending on the host terrane.
Uses & applications
Used as decorative and dimension stone, carved ornaments, and historically as a source rock associated with asbestos minerals; most pieces are collected rather than used commercially.
Geological facts
Often shows slickensided surfaces and may feel slightly soapy. Some serpentinite contains fibrous chrysotile, so avoid cutting, drilling, or creating dust unless tested and handled professionally.
Field identification & locations
Look for green coloration, waxy texture, veining, and relatively low hardness; it may scratch with a steel knife and commonly leaves a pale green-gray streak. Common in California, Italy, New Zealand, Canada, and convergent mountain belts.
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