sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

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

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

Identified July 9, 2026More sedimentary →

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Physical properties

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

Formation & geological history

Formed by the accumulation of siliceous remains of marine organisms or precipitation from silica-rich groundwater within limestone or chalk beds. Often Cretaceous in age.

Uses & applications

Historically used for stone tools (arrowheads), fire-starting, and flintlock firearms. Currently used as road aggregate and in some ceramics.

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 technological development due to its predictable fracturing.

Field identification & locations

Identified by its sharp, glass-like conchoidal fracture edges and ability to scratch glass. Commonly found in riverbeds, chalk cliffs, and as nodules in limestone regions.