metamorphic
Serpentinite (likely)
Serpentinite, composed mainly of serpentine-group minerals (Mg₃Si₂O₅(OH)₄), with possible magnetite, chromite, and talc
AI-generated identification · may be incorrectTypically dark green to black, mottled, waxy to greasy luster; Mohs hardness about 2.5–4. It commonly has a massive, fine-grained texture rather than visible crystal faces, with possible magnetic response from magnetite.
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Physical properties
Typically dark green to black, mottled, waxy to greasy luster; Mohs hardness about 2.5–4. It commonly has a massive, fine-grained texture rather than visible crystal faces, with possible magnetic response from magnetite.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite are hydrated and metamorphosed, commonly along oceanic crust and subduction zones. Most specimens represent ancient Paleozoic–Mesozoic tectonic belts, though age depends on locality.
Uses & applications
Used as decorative stone, carvings, countertops, and historically as a source of asbestos-bearing material; attractive pieces are collected, but fibrous varieties should not be cut or abraded.
Geological facts
The mottled green-black appearance and shiny patches are characteristic of serpentinization; associated chromite or magnetite may produce dark metallic grains.
Field identification & locations
Common in ophiolites and tectonic mélanges worldwide, including California, Italy, New Zealand, and the Appalachians. Confirm with a streak, hardness, density, and laboratory mineral analysis; visual identification is not definitive.
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