sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Variegated grays, tans, and dull whites with a dark gray core; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Luster: Waxy to dull

Identified March 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or by chemical precipitation in marine environments, occurring as nodules in limestone or chalk beds. Often associated with Cretaceous and Jurassic geological ages.

Uses & applications

Historically used for stone tools (arrowheads, knives) and strike-a-lights for fire making. Modern uses include road surfacing, decorative landscaping, and as an ingredient in ceramics.

Geological facts

Flint was one of the most important minerals for human survival during the Stone Age due to its ability to produce sharp edges when fractured. When struck against steel, it produces sparks used to ignite gunpowder or tinder.

Field identification & locations

Identify in the field by its distinctive 'chime' when struck, its sharp glass-like edges, and its inability to be scratched by a steel knife. Common in the UK (Chalk Downs), USA (Ohio, Texas), and across Europe.