sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Dark brown to black with a tan weathering crust; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Dark brown to black with a tan weathering crust
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation in marine environments; often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used in construction aggregate, as a gemstone (variety of jasper/agate), and for fire-starting in survival kits.

Geological facts

Flint was one of the most important materials for early humans because of its ability to fracture into sharp edges and produce sparks when struck against steel or iron pyrites.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture, sharp edges when broken, and inability to be scratched by a steel knife. Commonly found in riverbeds or within limestone outcrops.