metamorphic
Likely serpentinite
Serpentinite, composed mainly of serpentine-group minerals (chrysotile, lizardite, antigorite), commonly with magnetite and pyroxene remnants
AI-generated identification · may be incorrectDark green-gray, mottled, fine-grained, and waxy to dull; typically Mohs 2.5–4, with poor cleavage and an uneven fracture. The specimen appears massive rather than crystalline; exact identification requires testing because lighting and image resolution limit certainty.
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Physical properties
Dark green-gray, mottled, fine-grained, and waxy to dull; typically Mohs 2.5–4, with poor cleavage and an uneven fracture. The specimen appears massive rather than crystalline; exact identification requires testing because lighting and image resolution limit certainty.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite are hydrated during metamorphism, commonly along oceanic crust and plate-boundary faults. Serpentinization ranges from ancient Precambrian terrains to actively forming seafloor environments.
Uses & applications
Used as decorative and architectural stone, carving material, and occasionally aggregate; attractive polished pieces are collected, though fibrous varieties may contain asbestos-form serpentine and should not be cut or abraded without precautions.
Geological facts
Serpentinite is often strongly green from iron-bearing serpentine minerals and may contain black magnetite veins or rusty weathering. It is California’s official state rock.
Field identification & locations
Look for a relatively soft, green, mottled rock with a waxy surface; a steel knife may scratch it, and a magnet may respond weakly to magnetite. Common localities include California, Italy, Canada, New Zealand, and Greece.
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