sedimentary

Chert (River Stone)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs. Color: Tan, grey, brown. Luster: Dull to waxy. Structure: Microcrystalline/Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.5-2.8.

Hardness: 6
Color: Tan, grey, brown
Luster: Dull to waxy

Identified July 6, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs. Color: Tan, grey, brown. Luster: Dull to waxy. Structure: Microcrystalline/Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.5-2.8.

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Usually associated with marine limestone or as nodules in chalk. This specimen shows water-worn rounding, suggesting a fluvial (river) history.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges. Modernly used in landscaping, road construction aggregate, and as a decorative river rock.

Geological facts

Chert is so durable that it often survives long after the surrounding rock has eroded. It was the preferred material for making fire-starting flints in early history.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel) and smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds and gravel pits.