metamorphic
Weathered greenstone (likely serpentinite or chlorite-rich metamorphic rock)
Serpentinite/chlorite schist; commonly dominated by serpentine-group minerals, Mg-rich chlorite, talc, and magnetite
AI-generated identification · may be incorrectHardness typically 2.5–4 Mohs; mottled green, gray, and brown with dull to waxy luster, fine-grained texture, and irregular fracture. The specimen appears strongly weathered and lacks visible diagnostic crystals.
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Physical properties
Hardness typically 2.5–4 Mohs; mottled green, gray, and brown with dull to waxy luster, fine-grained texture, and irregular fracture. The specimen appears strongly weathered and lacks visible diagnostic crystals.
Formation & geological history
Formed when ultramafic mantle rocks, especially peridotite, were hydrated during low-temperature metamorphism; associated rocks may be Precambrian to Phanerozoic in age. Surface oxidation produces brown and rusty patches.
Uses & applications
Used as decorative stone, carvings, countertops, and historically as a source rock for asbestos-bearing minerals; ordinary pieces have little commercial value.
Geological facts
Greenstone is a broad field term, so exact identification requires tests or laboratory analysis. Serpentinite may feel unusually smooth or waxy and can leave a pale green streak.
Field identification & locations
Common in ophiolite belts, subduction zones, and tectonic fault zones worldwide, including California, Italy, New Zealand, and Canada. Check for a waxy feel, low hardness, green streak, and possible magnetism; avoid cutting or sanding unknown serpentinite because some varieties contain asbestos.
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