metamorphic
Likely serpentinized ultramafic rock (serpentinite)
Serpentinite; chiefly serpentine-group minerals, Mg₃Si₂O₅(OH)₄, possibly with magnetite, chromite, and brucite
AI-generated identification · may be incorrectTypically mottled olive-green to black, waxy or greasy luster, irregular massive texture, and occasional slick surfaces; Mohs hardness is about 2.5–4. The image is insufficient for confident mineral identification, and the specimen may also contain other green alteration minerals.
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Physical properties
Typically mottled olive-green to black, waxy or greasy luster, irregular massive texture, and occasional slick surfaces; Mohs hardness is about 2.5–4. The image is insufficient for confident mineral identification, and the specimen may also contain other green alteration minerals.
Formation & geological history
Forms when mantle-derived peridotite is hydrated and metamorphosed by fluids, commonly along fault zones and oceanic crust; formation ages vary from Precambrian to modern tectonic settings. It is not possible to determine age or exact composition from the photograph alone.
Uses & applications
Used as decorative stone, carved objects, aggregate, and historically as a source or host for asbestos minerals; jewelry-grade material is occasionally polished. Avoid cutting or grinding unknown serpentinite because some varieties contain hazardous fibrous asbestos.
Geological facts
The green color commonly results from serpentine minerals, while dark grains may be magnetite or chromite. A magnet, streak, hardness, acid, and asbestos-fiber inspection would substantially improve identification.
Field identification & locations
Common in ophiolites and tectonic belts, including California, the Appalachians, New Zealand, Italy, and Canada. Field clues include low density, green-black mottling, greasy feel, and sometimes magnetic response; confirm with hardness, streak, and laboratory testing.
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