sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: brown, tan, gray; Luster: waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: brown, tan, gray
Luster: waxy to dull

Identified July 17, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: brown, tan, gray; Luster: waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed in marine or freshwater environments via chemical precipitation or replacement of other minerals by silica-rich fluids. Can be billions of years old or from recent geological eras.

Uses & applications

Historically used for stone tools and weapons (knapping); currently used in construction as aggregate and occasionally as a flint-starter for fires.

Geological facts

Chert is so hard it will scratch glass and steel. It was one of the most important raw materials for early humans to create arrowheads and knives due to its sharp, glass-like edges when fractured.

Field identification & locations

Identify in the field by its smooth, waxy surface and its tendency to break into curved, sharp-edged flakes. Commonly found in limestone and dolomite beds or as river-worn nodules.