metamorphic
Rounded greenstone river cobble
Likely serpentinite or chlorite-rich metamorphic rock; exact identification requires testing
AI-generated identification · may be incorrectMassive, fine-grained, pale green-gray, weathered surface with faint foliation and matte to slightly waxy luster; likely Mohs 3–6 depending on composition. No visible crystals, cleavage, or fossils; shape reflects abrasion rather than crystal structure.
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Physical properties
Massive, fine-grained, pale green-gray, weathered surface with faint foliation and matte to slightly waxy luster; likely Mohs 3–6 depending on composition. No visible crystals, cleavage, or fossils; shape reflects abrasion rather than crystal structure.
Formation & geological history
Probably a glacial or stream-rounded cobble derived from altered ultramafic rock or greenschist-facies metamorphism. Such rocks commonly formed during ancient tectonic and hydrothermal processes, with age dependent on its source terrane.
Uses & applications
Used as landscaping stone, décor, lapidary material, and occasionally aggregate; attractive pieces may be polished, though this specimen appears natural and uncut.
Geological facts
Serpentinite commonly contains serpentine minerals and may include magnetite, chromite, or minor asbestos-form minerals. A streak, hardness, specific-gravity, and acid test would help distinguish it from greenstone, epidote rock, or weathered basalt.
Field identification & locations
Common in serpentinite belts, ophiolites, glacial deposits, and mountain streams. Look for a greasy/waxy feel, green veining, low-to-moderate density, and white streak; avoid cutting unknown serpentinite dust because some varieties can contain fibrous asbestos minerals.
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