metamorphic

Rounded greenstone river cobble

Likely serpentinite or chlorite-rich metamorphic rock; exact identification requires testing

AI-generated identification · may be incorrect

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.

Identified September 16, 2026More metamorphic →

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Physical properties

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.