metamorphic
Serpentinized ultramafic rock (likely serpentinite)
Serpentinite; chiefly serpentine-group minerals, with possible magnetite, olivine, pyroxene, and talc
AI-generated identification · may be incorrectHardness typically 2.5–4 Mohs; mottled dark green, olive, black, and brown with a waxy to dull luster. Usually fine-grained and massive, lacking obvious crystals; commonly somewhat dense and smooth when waterworn.
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Physical properties
Hardness typically 2.5–4 Mohs; mottled dark green, olive, black, and brown with a waxy to dull luster. Usually fine-grained and massive, lacking obvious crystals; commonly somewhat dense and smooth when waterworn.
Formation & geological history
Forms when mantle-derived peridotite is hydrated and metamorphosed by circulating fluids, commonly along oceanic crust and plate boundaries. Ages vary widely, from Precambrian to modern tectonic settings.
Uses & applications
Used as decorative stone, carvings, beads, countertops, and occasionally construction aggregate; attractive polished pieces have modest collecting value.
Geological facts
The green color comes from serpentine minerals formed during hydration of olivine- and pyroxene-rich rocks. Some serpentinite contains magnetite and may show weak attraction to a magnet.
Field identification & locations
Identify by its green-black mottling, smooth waxy surface, relatively low hardness, and possible magnetism; common in ophiolites and tectonic belts worldwide, including California, Italy, New Zealand, and the Appalachians.
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