metamorphic
Serpentine (likely serpentinite)
Serpentinite; chiefly serpentine-group minerals (antigorite, lizardite, chrysotile), commonly with magnetite and chromite
AI-generated identification · may be incorrectDark green to black, mottled and often waxy or greasy luster; typically massive with fibrous or scaly texture and no obvious cleavage. Hardness is about 2.5–4 Mohs, with variable density; the specimen’s polished-looking green-black pattern is consistent with serpentine.
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Physical properties
Dark green to black, mottled and often waxy or greasy luster; typically massive with fibrous or scaly texture and no obvious cleavage. Hardness is about 2.5–4 Mohs, with variable density; the specimen’s polished-looking green-black pattern is consistent with serpentine.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite undergo hydration and low-temperature metamorphism, commonly along oceanic crust and tectonic fault zones. Serpentinite ranges from ancient Precambrian bodies to young active plate-boundary occurrences.
Uses & applications
Used as decorative stone, carvings, countertops, and ornamental objects; historically used as a low-grade asbestos source where chrysotile is present. Attractive polished material has modest lapidary and collecting value.
Geological facts
Serpentinite may contain magnetite, giving it a dark appearance and occasional magnetic response. Chrysotile-bearing pieces should not be cut, drilled, or abraded because inhaled fibers are hazardous.
Field identification & locations
Common in ophiolites and subduction-related belts, including California, Oregon, Italy, New Zealand, and the Himalaya. Identify by its green-black waxy appearance, softness, streaking, and reaction to a steel point; confirmation requires microscopy or chemical testing.
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