sedimentary

Chert (Flint)

Chert (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs; Color: Gray, tan, white, and black mottled patterns; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture)

Hardness: 7 Mohs
Color: Gray, tan, white, and black mottled patterns
Luster: Dull to waxy

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Gray, tan, white, and black mottled patterns; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture)

Formation & geological history

Formed via the accumulation of silica-rich organic remains (such as diatoms or radiolaria) or chemical precipitation in marine environments; often found as nodules in limestone.

Uses & applications

Historically used for stone tools and starting fires; used today in road construction, as decorative river rock, and in jewelry (when polished).

Geological facts

Flint is a variety of chert that was essential to prehistoric humans because it fractures predictably into extremely sharp edges for knives and arrowheads.

Field identification & locations

Identified by its extreme hardness (scratches glass) and smooth, curved conchoidal fractures. Commonly found in gravel pits, riverbeds, and chalk/limestone chalk cliffs.