sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Grey, black, brown, or dull green; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline/Microcrystalline; Fracture: Conchoidal; Specific gravity: 2.65

Hardness: 6
Color: Grey, black, brown, or dull green
Luster: Waxy to vitreous

Identified June 26, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Grey, black, brown, or dull green; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline/Microcrystalline; Fracture: Conchoidal; Specific gravity: 2.65

Formation & geological history

Formed through the precipitation of silica-rich fluids within sedimentary host rocks, often as nodules or bedded layers. Usually occurs in limestone or chalk beds from Paleozoic to Cenozoic eras.

Uses & applications

Historically used for stone tools/weapons (knapping) and fire-starting. Currently used in road surfacing, grinding media, and occasionally as decorative gravel or gemstone (jasper varieties).

Geological facts

Chert was one of the first resources humans traded over long distances during the Stone Age. It breaks with a conchoidal fracture, creating razor-sharp edges.

Field identification & locations

Identify by its waxy appearance, extreme hardness (it will scratch glass), and the curved, shell-like (conchoidal) patterns on broken surfaces. Found worldwide in limestone formations.