metamorphic
Serpentine-rich serpentinite pebble
Serpentinite, composed chiefly of serpentine-group minerals (lizardite, antigorite, chrysotile), commonly with magnetite and minor brucite
AI-generated identification · may be incorrectTypically olive-green to gray-green, waxy to greasy luster, fine-grained and massive; Mohs hardness about 2.5–4, with poor or absent cleavage and specific gravity around 2.5–2.6. The smooth, rounded surface indicates natural water wear or tumbling.
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Physical properties
Typically olive-green to gray-green, waxy to greasy luster, fine-grained and massive; Mohs hardness about 2.5–4, with poor or absent cleavage and specific gravity around 2.5–2.6. The smooth, rounded surface indicates natural water wear or tumbling.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite undergo hydration and low-temperature metamorphism, commonly in oceanic crust and subduction zones. Most examples are Paleozoic to Mesozoic or younger, depending on the tectonic setting.
Uses & applications
Used as ornamental stone, carvings, countertops, and historically as a source of decorative “green marble”; some varieties are collectible. Chrysotile-bearing material should not be cut, drilled, or abraded because inhaled fibers are hazardous.
Geological facts
Serpentinite often contains a distinctive mottled green pattern and may be weakly magnetic from magnetite. It is the official state rock of California and occurs widely in tectonic mélange zones.
Field identification & locations
Identify it by its green color, low hardness, waxy feel, fine texture, and occasional dark veins or magnetism; a steel blade may scratch it. Common localities include California, Italy, New Zealand, Canada, and parts of the Appalachians.
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