metamorphic
Serpentinite (probable)
Serpentinite; chiefly serpentine-group minerals (antigorite, lizardite, chrysotile), commonly with magnetite and relict olivine/pyroxene
AI-generated identification · may be incorrectGreenish-gray, mottled and fine-grained with dull to waxy luster; Mohs hardness about 2.5–4, generally massive with no obvious cleavage. The dark metallic-looking patches may be magnetite or chromite, but the photograph is insufficient for certainty.
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Physical properties
Greenish-gray, mottled and fine-grained with dull to waxy luster; Mohs hardness about 2.5–4, generally massive with no obvious cleavage. The dark metallic-looking patches may be magnetite or chromite, but the photograph is insufficient for certainty.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite undergo low-temperature hydrothermal metamorphism and hydration, commonly along plate boundaries and ancient oceanic crust. Ages range from modern alteration to Precambrian occurrences.
Uses & applications
Used as a decorative and carving stone, dimension stone, and historically for architectural surfaces; asbestos-bearing varieties require health precautions. Attractive polished material has limited lapidary and collector use.
Geological facts
Serpentinite commonly preserves a mesh-like texture from altered olivine and may contain magnetite, making some pieces weakly magnetic. It is California’s official state rock.
Field identification & locations
Look for greasy/waxy green mottling, low hardness, and possible magnetism; a streak, acid, hardness, and thin-section test can distinguish it from chlorite-rich rocks or altered basalt. Common in ophiolites and subduction-zone mélanges worldwide.
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