metamorphic
Polished serpentine (likely green serpentinite)
Serpentinite; chiefly serpentine-group minerals, Mg₃Si₂O₅(OH)₄, with magnetite and possible chromite or carbonate inclusions
AI-generated identification · may be incorrectHardness about 2.5–4 Mohs; mottled olive-green, yellow-green, brown, and black coloration with a waxy to subvitreous luster. Usually massive and noncrystalline at hand-specimen scale, with irregular fracture and no prominent cleavage; density commonly 2.5–2.6 g/cm³.
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Physical properties
Hardness about 2.5–4 Mohs; mottled olive-green, yellow-green, brown, and black coloration with a waxy to subvitreous luster. Usually massive and noncrystalline at hand-specimen scale, with irregular fracture and no prominent cleavage; density commonly 2.5–2.6 g/cm³.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite are hydrothermally altered by water, commonly in oceanic crust and subduction zones. Individual alteration ages vary widely from Precambrian to modern tectonic settings.
Uses & applications
Used as a decorative and ornamental stone, beads, carvings, cabochons, and polished specimens; massive serpentinite has also been used locally as dimension stone. Fibrous varieties may contain asbestos and should not be cut or abraded without proper controls.
Geological facts
The dark reddish-brown patches may be iron oxides or other associated minerals, while the green body is characteristic of serpentine minerals. Serpentinite is California’s state rock.
Field identification & locations
Common in tectonic belts and ophiolites, including California, Italy, New Zealand, Canada, and the Ural Mountains; identify by its low hardness, waxy green appearance, and mottled pattern. This polished specimen is consistent with serpentine, though exact locality and inclusions require testing.
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