metamorphic
Serpentinite (likely serpentinized ultramafic rock)
Serpentinite; chiefly serpentine-group minerals (Mg₃Si₂O₅(OH)₄), commonly with magnetite, chromite, and relict olivine/pyroxene
AI-generated identification · may be incorrectDark green to gray-green, finely mottled and waxy to slightly silky; commonly massive with faint veining. Mohs hardness about 2.5–4, specific gravity roughly 2.5–2.7; poor or absent cleavage, typically microcrystalline rather than visibly crystalline.
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Physical properties
Dark green to gray-green, finely mottled and waxy to slightly silky; commonly massive with faint veining. Mohs hardness about 2.5–4, specific gravity roughly 2.5–2.7; poor or absent cleavage, typically microcrystalline rather than visibly crystalline.
Formation & geological history
Forms when mantle-derived peridotite is hydrated and altered by circulating water, usually along oceanic crust, subduction zones, and major faults. Ages range from ancient Precambrian bodies to much younger active tectonic complexes.
Uses & applications
Used as dimension stone, decorative tile, carvings, and lapidary material; historically marketed as green marble. Avoid cutting or generating dust without testing, because some serpentinite contains fibrous chrysotile asbestos.
Geological facts
The cylindrical object appears polished or cored, so texture and color are more diagnostic than natural surface luster. Vein patterns may contain carbonate or quartz.
Field identification & locations
Field clues include green mottling, unusually low hardness, waxy feel, and association with mafic or ultramafic rocks; it may scratch with a steel knife. Common in California, the Appalachians, the Alps, New Zealand, and ophiolite belts worldwide.
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