sedimentary

Chert (Flint)

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs; Color: Brown, grey, black; Luster: Waxy to vitreous; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 Mohs
Color: Brown, grey, black
Luster: Waxy to vitreous

Identified July 6, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Brown, grey, black; Luster: Waxy to vitreous; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed primarily in marine environments where microcrystalline silica precipitates from water or replaces organic material (like limestone or chalk) during diagenesis.

Uses & applications

Historically used for stone tools and starting fires; currently used as road aggregate, in glass making, and by flintknapping hobbyists.

Geological facts

Flint is a variety of chert. When struck against steel, it creates sparks due to the friction oxidizing iron particles. It has been used by humans for millions of years for tools.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture, sharp edges when broken, and extreme hardness (it will scratch glass). Commonly found in sedimentary basins.