sedimentary

Chert / Flint

Silicon dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Grey, black, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Hardness: 6
Color: Grey, black, or tan
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Grey, black, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Formation & geological history

Formed from the recrystallization of silica-rich organic remains or chemical precipitation in marine environments; age varies from Precambrian to modern seafloor deposits.

Uses & applications

Historically used for stone tools and starting fires; currently used in construction aggregate and as a semi-precious gemstone in jewelry.

Geological facts

Flint is a variety of chert that was essential to prehistoric humans for making sharp blades, arrowheads, and spears due to its predictable conchoidal fracturing.

Field identification & locations

Identify by its very smooth, glass-like fracture surfaces and extreme hardness (will scratch glass). Commonly found in limestone or chalk beds as nodules.