sedimentary

Black Flint

Chert (Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs; Color: Black, dark gray, or charcoal; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Hardness: 7 Mohs
Color: Black, dark gray, or charcoal
Luster: Waxy to vitreous

Identified July 9, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Black, dark gray, or charcoal; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed in sedimentary environments, typically as nodules in chalk or limestone through the replacement of calcium carbonate by silica. Often dates from the Cretaceous period.

Uses & applications

Historically used for stone tools and firearms; currently used in jewelry (as cabochons), architectural facing, and as a component in ceramics.

Geological facts

Flint was the primary material used by prehistoric humans to create sharp edges and ignite fires. The dark color is often due to organic impurities trapped within the silica structure.

Field identification & locations

Identified by its distinctive conchoidal fracture (smooth, curved breaks) and extreme sharpness. Commonly found in the UK (Dover), France, and the USA. Collectors look for smooth nodules or worked artifacts.