sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs; Color: Brown, black, or grey; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

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

Identified June 18, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Brown, black, or grey; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed primarily by the accumulation of siliceous remains of microscopic organisms like diatoms and radiolarians, or through chemical precipitation in marine environments. Found in sedimentary layers throughout geologic history from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges; currently used as a road aggregate, in glass manufacturing, and as a decorative stone.

Geological facts

Chert has been used by humans for millions of years to create fire pulses when struck against steel. It is one of the most durable sedimentary rocks.

Field identification & locations

Identified by its waxy luster, extreme hardness (scratches glass), and characteristic curved, shell-like (conchoidal) fractures. Commonly found in limestone or chalk beds globally.