sedimentary

Chert (White Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs), Color: White to light grey, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Identified June 19, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs), Color: White to light grey, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like diatoms or radiolarians) or chemical precipitation from groundwater. Typically found in marine sedimentary environments (limestone/chalk beds).

Uses & applications

Historically used for making stone tools (arrowheads/scrapers); currently used in road construction, as abrasive material, and sometimes as landscaping gravel.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture creates razor-sharp edges. It is chemically identical to quartz but has a much finer grain structure.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel) and smooth, shell-like (conchoidal) breaks. Often found as nodules within limestone or as river pebbles.