sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7.0 (Mohs scale); Color: Gray, brown, or tan; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6

Hardness: 6
Color: Gray, brown, or tan
Luster: Waxy to vitreous

Identified May 20, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7.0 (Mohs scale); Color: Gray, brown, or tan; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed primarily through the chemical precipitation of silica from groundwater or the accumulation of siliceous skeletal remains (diatoms/radiolarians) in marine environments. Common in limestone or chalk beds.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) and starting fires. Currently used in jewelry (as jasper or agate), construction aggregate, and as a collector's specimen.

Geological facts

Flint was one of the most important minerals for early human development, enabling the creation of sharp tools and the ability to strike fire using steel.

Field identification & locations

Identified in the field by its sharp, curved (conchoidal) fracture edges, waxy feel, and its ability to scratch glass or steel. Often found as nodules within limestone or as river-worn cobbles.