sedimentary

Chert (Flint)

Chert (SiO2)

Hardness: 7 Mohs; Color: Gray, tan, white, brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs
Color: Gray, tan, white, brown
Luster: Waxy to dull

Identified July 13, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Gray, tan, white, brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed via the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments, often replacing limestone or chalk.

Uses & applications

Historically used for making stone tools (arrowheads). Currently used for road gravel, decorative landscaping, and as a strike-stone for fire-starting.

Geological facts

Flint is a variety of chert that occurs in chalk or marly limestone. It was one of the most important minerals for early human civilizations due to its predictable breaking pattern.

Field identification & locations

Identify in the field by its very smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Commonly found as nodules in limestone beds or as stream pebbles.