sedimentary

Rounded gray river cobble

Likely fine-grained sandstone, siltstone, or metamorphosed equivalent; exact identification requires a fresh surface and tests

AI-generated identification · may be incorrect

Dense, smooth, and well-rounded with a dull gray-green color and very fine granular texture; likely Mohs 5–7, with no visible crystals or cleavage. Luster is dull to slightly silky; composition may include quartz, feldspar, and clay minerals, possibly with chlorite or mica.

Identified August 20, 2026More sedimentary →

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At a glance

Common name: Rounded gray river cobble
Scientific name: Likely fine-grained sandstone, siltstone, or metamorphosed equivalent; exact identification requires a fresh surface and tests
Category: sedimentary
Identified: August 20, 2026
Method: Standard

AI Estimated Value

$1–$10 as an ordinary cobble; approximately $10–$40 if unusually attractive, polished, or sold as a lapidary specimen.

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

Natural fluvial abrasion produced the rounded shape. The original rock likely formed from compacted fine sediment, potentially millions to hundreds of millions of years ago, though its age cannot be determined visually.

Uses & applications

Primarily a landscaping, decorative, or lapidary stone; occasionally used for cabochons or polished stones if it takes a good finish. Not enough information to recommend construction use.

Geological facts

The subtle green-gray tone can indicate chlorite-bearing sedimentary or metamorphic material, but lighting and surface weathering can be misleading.

Field identification & locations

Look for consistent fine grains, absence of vesicles, and a natural weathering rind; a streak, hardness, acid, and fresh-break test would distinguish sandstone, slate, basalt, and greenstone. Common in streambeds, beaches, and glacial deposits.