metamorphic
Serpentinite
Serpentinite; chiefly serpentine-group minerals (antigorite, lizardite, chrysotile), commonly with magnetite, chlorite, and talc
AI-generated identification · may be incorrectTypically dark green, black, or mottled gray-green with waxy to dull luster and commonly slickensided surfaces; Mohs hardness about 2.5–4, low-to-moderate density, and massive rather than visibly crystalline texture. The yellow-green patches and veining are characteristic of serpentinization.
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Physical properties
Typically dark green, black, or mottled gray-green with waxy to dull luster and commonly slickensided surfaces; Mohs hardness about 2.5–4, low-to-moderate density, and massive rather than visibly crystalline texture. The yellow-green patches and veining are characteristic of serpentinization.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite react with water during hydrothermal alteration, often in oceanic crust and subduction zones. Many exposures are Paleozoic to Mesozoic or younger fragments of obducted ophiolites.
Uses & applications
Used as decorative and architectural stone, carvings, countertops, and historically for heat-resistant objects; asbestos-bearing varieties require caution and are not suitable for indoor use. Collectible value is generally modest unless unusually patterned or polished.
Geological facts
Serpentinite is California’s state rock and commonly records ancient oceanic mantle. Some specimens contain chrysotile asbestos, so avoid cutting, drilling, or generating dust without proper testing and controls.
Field identification & locations
Identify by its mottled green-black color, waxy feel, low hardness, and association with tectonic faults or ophiolite belts; it may scratch with a steel knife and often has magnetite-rich dark spots. Common worldwide in Alpine, Appalachian, Californian, New Zealand, and other subduction-related terrains.
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