metamorphic
Greenstone, likely serpentinite
Serpentinite; predominantly serpentine-group minerals, Mg₃Si₂O₅(OH)₄, with possible magnetite, chlorite, and talc
AI-generated identification · may be incorrectDark olive-green, mottled, fine-grained rock with dull to waxy luster and no obvious crystals; hardness is typically 2.5–4 Mohs, with variable specific gravity around 2.5–2.6. The specimen’s appearance is consistent with serpentinized ultramafic rock, though a photo cannot exclude chlorite-rich greenstone.
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Physical properties
Dark olive-green, mottled, fine-grained rock with dull to waxy luster and no obvious crystals; hardness is typically 2.5–4 Mohs, with variable specific gravity around 2.5–2.6. The specimen’s appearance is consistent with serpentinized ultramafic rock, though a photo cannot exclude chlorite-rich greenstone.
Formation & geological history
Forms when mantle-derived peridotite is hydrated and metamorphosed by circulating fluids, commonly in oceanic crust and tectonic suture zones. Serpentinization ranges from ancient Precambrian terrains to modern settings; its exact age is locality-dependent.
Uses & applications
Used as decorative stone, carvings, talismans, and occasionally architectural facing; historically used for tools and ornamental objects. Common pieces have modest collector value.
Geological facts
Serpentinite often contains slick, waxy surfaces and dark magnetite grains, and may weather to a pale green or brown crust. Some varieties contain asbestos-form serpentine, so avoid cutting or generating dust unless tested.
Field identification & locations
Common in California, Vermont, Italy, New Zealand, Canada, and many ophiolite belts. Check for a waxy feel, green veining, relatively low hardness, and possible magnetism; a streak, hardness, and mineralogical test would improve identification.
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