sedimentary

Weathered river cobble, possibly sandstone or volcanic tuff

Indeterminate lithology; likely fine-grained sandstone/siltstone, with possible iron-oxide veining

AI-generated identification · may be incorrect

Large rounded, flattened cobble with tan-brown color, dull earthy luster, fine-grained texture, faint reddish-brown vein, and surface weathering. Hardness is approximately 4–6 Mohs if sandstone or tuff; cleavage is absent, and specific gravity likely 2.2–2.7.

Identified September 3, 2026More sedimentary →

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At a glance

Common name: Weathered river cobble, possibly sandstone or volcanic tuff
Scientific name: Indeterminate lithology; likely fine-grained sandstone/siltstone, with possible iron-oxide veining
Category: sedimentary
Identified: September 3, 2026
Method: Standard

AI Estimated Value

About $5–$30 as an ordinary large cobble; potentially $30–$100 if provenance, unusual mineralization, or attractive polished texture is demonstrated.

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

Its smooth shape indicates prolonged abrasion in a river, beach, or glacial setting; the reddish coloration likely reflects iron oxidation. Exact age and formation environment cannot be determined reliably from the photograph.

Uses & applications

Usually a landscaping, decorative, or curiosity specimen; it has little industrial or jewelry value unless cutting reveals attractive texture or mineralization.

Geological facts

The dark green-gray patch may be a secondary mineral, lichen, or attached material rather than part of the rock. A fresh broken or sawn surface would be needed for confident identification.

Field identification & locations

Look for grain size, reaction to dilute hydrochloric acid, and hardness: sandstone commonly shows visible grains, while volcanic tuff is ash-textured. Common analogous cobbles occur in river gravels worldwide.