sedimentary

Chert (Flint)

Chert (SiO2)

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

Hardness: 7 on Mohs scale
Color: Brown, grey, or tan
Luster: Waxy to dull

Identified June 21, 2026More sedimentary →

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Physical properties

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

Formation & geological history

Formed from the accumulation of siliceous remains of organisms or through chemical precipitation in marine or groundwater environments. It can be found in various geological ages ranging from Precambrian to Cenozoic.

Uses & applications

Historically used for making sharp tools and weapons (arrowheads, knives); modern use in construction aggregates and as fire-starting flints.

Geological facts

Chert is so hard it can scratch steel and was used by ancient humans for the first industrial-scale mining. When struck against steel, it produces sparks, a property used for centuries in flintlock firearms.

Field identification & locations

Look for a microcrystalline texture, waxy appearance, and sharp, shell-like (conchoidal) fractures. It is commonly found in limestone or chalk beds and along riverbanks.