sedimentary

Chert / River Pebble

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on the Mohs scale. Luster: Dull, waxy, or earthy. Color: Brownish-gray with tan or reddish weathering crust/banding. Structure: Cryptocrystalline, smooth water-worn texture with conchoidal fracture potential.

Hardness: 6
Color: Brownish-gray with tan or reddish weathering crust/banding
Luster: Dull, waxy, or earthy

Identified July 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation and recrystallization of silica-rich organic remains or chemical precipitation in sedimentary environments, followed by natural erosion, tumbling, and smoothing in a river bed or beach setting.

Uses & applications

Commonly used as aggregate, landscaping gravel, river rock filler, and historically for stone tools such as arrowheads due to its sharp conchoidal fracture.

Geological facts

River pebbles made of chert or fine-grained quartzite are extremely durable and can travel hundreds of miles down river systems, becoming rounded and polished by natural water action over thousands to millions of years.

Field identification & locations

Identified by its extreme smoothness, rounded wedge shape, hard surface that resists scratching with steel, and distinct brownish color zones from iron-rich weathering. Widely found along riverbanks, lake shores, and glacial deposits globally.

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