sedimentary

Chert (Flint)

Chert (Silicon Dioxide, SiO2)

Hardness: 7 (Mohs scale); Color: White, cream, gray; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: White, cream, gray
Luster: Waxy to dull

Identified June 20, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: White, cream, gray; 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 organic remains (like diatoms or radiolaria) or chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to sharp edges; currently used as road surface material, in construction, and as fire-starting flints.

Geological facts

Chert was one of the most important minerals for prehistoric humans because it breaks with a conchoidal fracture, creating razor-sharp edges. It is chemically identical to quartz but has a different microscopic structure.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel), waxy texture, and shell-like (conchoidal) breaking pattern. Common in sedimentary basins worldwide.