sedimentary

Chert (Black Flint)

Silicon Dioxide (SiO2)

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

Hardness: 7 on Mohs scale
Color: Black, dark grey
Luster: Waxy to dull

Identified March 27, 2026More sedimentary →

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Physical properties

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

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine or groundwater environments. Most specimens are found in limestone or chalk beds and range from Precambrian to Cenozoic geological ages.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to its sharp edges; used in early firearms (flintlocks); currently used as a raw material for ceramics, construction aggregate, and as a semi-precious gemstone in jewelry when polished.

Geological facts

Flint was one of the first materials used by early humans for fire-starting and weaponry. When struck against steel or iron pyrites, flint creates sparks that can ignite tinder.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture pattern and its ability to scratch glass. It is commonly found in gravel beds, riverbanks, and within limestone outcrops. Collectors look for pieces with unique inclusions or aesthetic banding.