sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Brown, tan, or dark grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Brown, tan, or dark grey
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brown, tan, or dark grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments, often replacing limestone or chalk.

Uses & applications

Historically used for stone tools and starting fires; currently used as a road aggregate, in jewelry as cabochons, and as a decorative stone.

Geological facts

Flint was a vital resource for prehistoric humans due to its ability to break into sharp edges. It produces sparks when struck against steel, making it the primary mechanism for flintlock firearms.

Field identification & locations

Identify by its characteristic conchoidal fracture (smooth, curved breaks) and its ability to scratch glass. Commonly found as nodules in chalk or limestone deposits.