sedimentary

Chert (Flint)

Chert (SiO2)

Hardness: 7 Mohs scale; Color: Grey, brown, or tan; Luster: Waxy to dull; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

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

Identified June 11, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Grey, brown, or tan; Luster: Waxy to dull; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed by the precipitation of silica from water, often replacing organic material or filling voids in limestone. Can be biogenic (from radiolarian or diatom skeletons) or chemical.

Uses & applications

Historically used for stone tools and starting fires (striker). Modern uses include road aggregates, jewelry (if colorful), and as an abrasive in some industrial processes.

Geological facts

Flint is a variety of chert that occurs in chalk or marly limestone. It was the primary material for the Stone Age tool industry because of its predictable conchoidal fracturing.

Field identification & locations

Identify in the field by its sharp, curved (conchoidal) edges when broken and its ability to scratch glass. It is often found as nodules or layers within limestone formations.