igneous and sedimentary

Rounded river pebbles, likely basalt and sandstone/conglomerate

Probable basalt (dark specimen) and ferruginous sandstone or weathered conglomerate (tan specimen)

AI-generated identification · may be incorrect

The dark pebble is fine-grained, charcoal-black, dull to weakly metallic, and likely basalt; the tan pebble is fine-grained, porous, rounded, and probably sandstone or weathered volcanic rock. Estimated hardness is about 5–6 for basalt and 4–7 for sandstone, with no obvious cleavage;…

Identified September 4, 2026More igneous and sedimentary →

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At a glance

Common name: Rounded river pebbles, likely basalt and sandstone/conglomerate
Scientific name: Probable basalt (dark specimen) and ferruginous sandstone or weathered conglomerate (tan specimen)
Category: igneous and sedimentary
Identified: September 4, 2026
Method: Standard

AI Estimated Value

Typically $0–$5 each; attractive polished or demonstrably unusual specimens may sell for approximately $5–$20.

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

These are water-worn clasts eroded from older bedrock and rounded in a stream, river, or beach environment. Their precise geological age cannot be determined from the photograph; basalt commonly forms from cooling lava, while sandstone forms by lithification of sediment.

Uses & applications

Commonly used as landscaping, decorative stone, aggregate, and occasional lapidary material; these ordinary pebbles have little jewelry value.

Geological facts

The strong rounding indicates prolonged transport or wave action. The dark pebble may contain plagioclase and pyroxene, while the tan stone may contain quartz, feldspar, iron oxides, or volcanic ash.

Field identification & locations

Test with a steel knife or glass, inspect a broken face, and use dilute hydrochloric acid to check for carbonate cement. Basalt is widespread in volcanic regions; sandstone and mixed river gravel occur globally.