sedimentary
Black Flint
Chert (Microcrystalline Quartz, SiO2)
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
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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.
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