sedimentary

Rounded brown chert (flint) pebble

Microcrystalline quartz (SiO₂), commonly with iron-oxide staining

AI-generated identification · may be incorrect

Hardness about 7 Mohs; brown to ochre, opaque, fine-grained, and dull to waxy-lustrous. It has no visible crystals or cleavage, conchoidal fracture, and typical specific gravity near 2.6.

Identified September 10, 2026More sedimentary →

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Physical properties

Hardness about 7 Mohs; brown to ochre, opaque, fine-grained, and dull to waxy-lustrous. It has no visible crystals or cleavage, conchoidal fracture, and typical specific gravity near 2.6.

Formation & geological history

Chert forms when silica precipitates or replaces carbonate sediments, often from microscopic marine organisms; the exact geological age cannot be determined from the image. Its smooth, rounded shape indicates transport and abrasion in a river, beach, or glacial deposit.

Uses & applications

Used historically for sharp tools and fire-starting; attractive pieces may be tumbled or used as low-cost decorative stones. It is generally not used as a major construction stone in pebble form.

Geological facts

Chert can produce exceptionally sharp edges when fractured, and flint is a dark, often organic-rich variety. Brown coloration commonly results from hydrated iron oxides.

Field identification & locations

Identify it by its uniform texture, lack of visible grains, waxy surface, and glassy conchoidal break; a steel file should not scratch it. Common in gravel beds, limestone regions, river channels, and beaches.