metamorphic
Likely serpentinite or serpentinized ultramafic rock
Serpentinite; chiefly serpentine-group minerals (antigorite, lizardite, chrysotile), commonly with magnetite and relict olivine/pyroxene
AI-generated identification · may be incorrectDark green-gray, mottled and massive with a dull to waxy luster; Mohs hardness about 2.5–4, typically low cleavage, fine-grained to subtly fibrous, and relatively dense (specific gravity about 2.5–2.7). The photograph is somewhat blurry, so exact identification is uncertain.
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Physical properties
Dark green-gray, mottled and massive with a dull to waxy luster; Mohs hardness about 2.5–4, typically low cleavage, fine-grained to subtly fibrous, and relatively dense (specific gravity about 2.5–2.7). The photograph is somewhat blurry, so exact identification is uncertain.
Formation & geological history
Forms when mantle-derived peridotite is hydrated and metamorphosed by water, commonly along oceanic crust and subduction-zone faults. Serpentinization ranges from ancient Precambrian to modern geological activity.
Uses & applications
Used as decorative and architectural stone, carvings, countertops, and occasionally as a source of asbestos-bearing material; attractive pieces are collected as cabinet specimens.
Geological facts
Serpentinite may show slick, waxy surfaces and can contain magnetite, making it weakly magnetic. Chrysotile-bearing varieties should not be cut, drilled, or abraded because inhaled fibers are hazardous.
Field identification & locations
Likely if the specimen is greenish, unusually smooth or waxy, dense, and weakly magnetic; a streak, hardness, magnet test, and fresh surface would help confirm it. Common locations include California, Italy, New Zealand, Canada, and the Appalachian and Alpine belts.
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