metamorphic
Serpentinite (likely serpentine-rich rock)
Serpentine-group minerals, chiefly antigorite/lizardite; commonly with magnetite, brucite, or relict olivine
AI-generated identification · may be incorrectDark olive-green to gray, mottled and fine-grained with a waxy to dull luster; Mohs hardness about 2.5–4, with no obvious cleavage and irregular fracture. The small specimen appears rough and granular, but lighting limits certainty.
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Physical properties
Dark olive-green to gray, mottled and fine-grained with a waxy to dull luster; Mohs hardness about 2.5–4, with no obvious cleavage and irregular fracture. The small specimen appears rough and granular, but lighting limits certainty.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite hydrate during low-temperature metamorphism, commonly along oceanic crust and fault zones. Serpentinite ranges from Precambrian to modern geological settings.
Uses & applications
Used as decorative stone, carvings, countertops, and occasionally jewelry; historically used as a source of asbestos-group minerals. Small unpolished fragments generally have little commercial value.
Geological facts
Serpentinite may contain magnetite and can show weak magnetism; some varieties contain chrysotile asbestos, so avoid cutting, sanding, or creating dust. Its green color reflects hydrated magnesium silicates.
Field identification & locations
Identify by green-black color, waxy texture, low hardness, and association with ultramafic terrain; a steel nail may scratch it. Common localities include California, Italy, New Zealand, Canada, and the Appalachian and Alpine belts.
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