metamorphic
Serpentinite (likely polished/tumbled)
Serpentinite; chiefly antigorite, lizardite, and chrysotile-group serpentine minerals, commonly with magnetite and minor carbonate
AI-generated identification · may be incorrectTypically green-gray to black, waxy or silky luster, fine-grained and massive; Mohs hardness about 2.5–4, specific gravity 2.5–2.6, with no obvious cleavage. The streaked fibrous appearance and rusty magnetite/iron-oxide patches fit serpentinite.
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Physical properties
Typically green-gray to black, waxy or silky luster, fine-grained and massive; Mohs hardness about 2.5–4, specific gravity 2.5–2.6, with no obvious cleavage. The streaked fibrous appearance and rusty magnetite/iron-oxide patches fit serpentinite.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite are hydrated during low-temperature metamorphism, commonly along tectonic plate boundaries and faults. Specimen age depends on its source, often Paleozoic to Mesozoic or younger tectonic complexes.
Uses & applications
Used as decorative stone, carvings, countertops, and ornamental tumbled material; historically used as a jade substitute. Chrysotile-bearing varieties may contain asbestos and should not be cut, drilled, or powdered without proper controls.
Geological facts
Serpentinite often contains magnetite, producing dark specks and occasional weak magnetism, while weathering creates rusty brown staining. It is California’s official state rock.
Field identification & locations
Common in ophiolites and subduction-zone mélanges, including California, Oregon, British Columbia, the Alps, New Zealand, and Greece. Identify it by its soft waxy surface, green-gray color, slick feel, and possible magnetism; visual identification is not definitive.
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