metamorphic

Serpentinite

Serpentinite, dominated by serpentine-group minerals (chrysotile, lizardite, antigorite), commonly with magnetite and chlorite

AI-generated identification · may be incorrect

Typically dark green to black, mottled, waxy to greasy luster, and massive or finely fibrous; Mohs hardness is about 2.5–5.5, with poor cleavage and specific gravity near 2.5–2.6. The specimen’s green-black color and mottled texture are consistent with serpentinite, though photo identification is not definitive.

Identified September 12, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when ultramafic mantle rocks such as peridotite are hydrated during hydrothermal alteration, commonly along faults and subduction zones. It can form from Precambrian through modern geological settings.

Uses & applications

Used as decorative stone, carvings, countertops, and ornamental specimens; historically used as a source of asbestos-bearing material. Avoid cutting or grinding unknown samples because some serpentinite contains fibrous chrysotile asbestos.

Geological facts

Serpentinite is California’s state rock and commonly contains magnetite, giving some pieces a magnetic response. It is often associated with chromite, talc, and nickel-bearing minerals.

Field identification & locations

Field clues include a green-black mottled appearance, relatively soft surface, waxy feel, and possible magnetism; a streak, hardness, and asbestos-safe laboratory test help confirm it. Common localities include California, the Alps, New Zealand, Japan, and ophiolite belts worldwide.