metamorphic
Likely serpentinized ultramafic rock (serpentinite)
Serpentinite; chiefly serpentine-group minerals (Mg₃Si₂O₅(OH)₄), with possible magnetite, chromite, and relict olivine/pyroxene
AI-generated identification · may be incorrectDark olive-gray to brown, mottled and weakly foliated, with a waxy to dull luster; Mohs hardness about 2.5–4, commonly massive, with poor cleavage and specific gravity roughly 2.5–2.7. The image is not sufficient for definitive identification.
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Physical properties
Dark olive-gray to brown, mottled and weakly foliated, with a waxy to dull luster; Mohs hardness about 2.5–4, commonly massive, with poor cleavage and specific gravity roughly 2.5–2.7. The image is not sufficient for definitive identification.
Formation & geological history
Forms when mantle-derived peridotite is hydrated and metamorphosed by water, commonly along oceanic crust, subduction zones, and fault zones. Formation ages vary widely from Paleozoic to modern tectonic settings.
Uses & applications
Used as decorative stone, carving material, aggregate, and historically as asbestos-bearing stone; attractive polished pieces may be collected, but fibrous varieties should not be cut or powdered.
Geological facts
Often contains magnetite, giving some specimens a magnetic response; associated minerals may include talc, chlorite, and chromite.
Field identification & locations
Common in ophiolites and tectonic belts, including California, Italy, New Zealand, and the Appalachians. Check for a green waxy surface, black magnetite specks, low hardness, and possible weak magnetism; testing or thin-section analysis is recommended.
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