sedimentary

Polished dark river pebble

Likely fine-grained basalt or chert; exact identification requires testing

AI-generated identification · may be incorrect

Dark brown to black, smooth and glossy from natural or human polishing, with no visible crystals. Likely hardness about 6–7 Mohs and specific gravity roughly 2.6–3.0; cleavage is absent or indistinct.

Identified August 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Probably a water-worn cobble shaped by abrasion in a stream or beach environment; if basalt, it formed from rapidly cooled lava, while chert formed from microcrystalline silica. Geological age cannot be determined from the photograph.

Uses & applications

Used as a decorative stone, lapidary cabochon, craft material, or garden/landscaping pebble; generally little commercial value unless it has unusual provenance or attractive patterning.

Geological facts

The rounded form and uniformly fine texture indicate strong abrasion and fine grain. A glassy appearance may result from wetting or polishing rather than natural crystal luster.

Field identification & locations

Check streak, hardness, density, and reaction to acid: chert scratches glass and gives a white streak; basalt is typically heavier, duller, and may contain tiny feldspar crystals. Common examples occur in stream gravels and volcanic terrains.