metamorphic

Rounded banded metamorphic cobble, likely greenstone or serpentinite

Probable greenschist-facies metavolcanic rock (chlorite–actinolite schist) or serpentinized ultramafic rock

AI-generated identification · may be incorrect

Green-gray to brown, strongly streaked/banded, fine-grained, with dull to slightly waxy luster and no visible large crystals; estimated Mohs hardness 3–6, depending on chlorite/serpentine versus harder amphibole and quartz. The wet surface enhances its dark green mineral bands.

Identified September 5, 2026More metamorphic →

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At a glance

Common name: Rounded banded metamorphic cobble, likely greenstone or serpentinite
Scientific name: Probable greenschist-facies metavolcanic rock (chlorite–actinolite schist) or serpentinized ultramafic rock
Category: metamorphic
Identified: September 5, 2026
Method: Standard

AI Estimated Value

$0–$10 as a common creek cobble; approximately $10–$50 if unusually attractive, polished, or confidently identified.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Likely formed when basaltic or ultramafic rock was altered by heat, pressure, and hydrothermal fluids during regional metamorphism; precise age and identity require thin-section or chemical testing. The rounded shape indicates prolonged stream transport and abrasion.

Uses & applications

Ordinary specimens have little commercial value; related greenstone is used locally as aggregate, landscaping stone, and sometimes ornamental material. Attractive polished pieces may be sold as lapidary rough or display stones.

Geological facts

Greenstone commonly contains chlorite, epidote, actinolite, albite, and quartz; serpentinite instead is dominated by serpentine minerals, often with magnetite. A magnet, streak, hardness, and acid test can help distinguish alternatives.

Field identification & locations

Look for dense green-black color, foliation or streaking, and a fine crystalline texture; test an inconspicuous area because the specimen is wet. Common in metamorphic belts and streambeds downstream from them.