sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on the Mohs scale; Color: typically gray, brown, or tan; Luster: waxy to dull; Crystal structure: cryptocrystalline (microscopic quartz); Cleavage: none, exhibits distinct conchoidal (shell-like) fracture; Specific Gravity: 2.65.

Hardness: 7 on the Mohs scale
Color: typically gray, brown, or tan
Luster: waxy to dull

Identified March 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of silica in sedimentary environments, often replacing organic material or filling cavities in limestone/chalk. Found in formations ranging from Precambrian to recent geological ages.

Uses & applications

Historically used for stone tools (arrowheads/knives) and fire-starting. Currently used as road aggregate, in glass manufacturing, and as decorative gravel.

Geological facts

Chert was one of the most vital resources for prehistoric humans because its predictable fracture pattern allowed for the creation of sharp blades and tools, a technology known as knapping.

Field identification & locations

Identify in the field by its waxy texture and sharp, curved edges when broken. It cannot be scratched by a steel knife and will spark when struck against steel. Commonly found in riverbeds or embedded in limestone cliffs.