sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: White, grey, or tan; Luster: Waxy to dull; Crystal structure: Microcrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: White, grey, or tan
Luster: Waxy to dull

Identified July 12, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: White, grey, or tan; Luster: Waxy to dull; Crystal structure: Microcrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed as nodules or layered deposits in limestone or chalk beds by the accumulation of siliceous remains of marine organisms or through chemical precipitation of silica-rich groundwater. Geological age varies from Precambrian to Recent.

Uses & applications

Historically used for stone tools and starting fires; currently used in construction aggregate, road surfacing, and as a component in ceramics and glass.

Geological facts

Flint, a variety of chert, was the most important material for early human technology. When struck against steel or pyrite, it produces sparks used to ignite fires. It breaks with extremely sharp edges, making it ideal for blades.

Field identification & locations

Identify in the field by its smooth, waxy texture and characteristic shell-like (conchoidal) fractures. Common in river beds, beaches, and chalk cliffs worldwide. Collectors look for unique colors or fossil inclusions.