Sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Gray, black, tan, or dark brown; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Gray, black, tan, or dark brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, black, tan, or dark brown; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed by the accumulation of siliceous remains of organisms like diatoms or radiolarians, or through chemical precipitation in marine environments. It is often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Modern uses include road surfacing, glass manufacture, and as decorative gravel.
Geological facts
Flint was one of the most important minerals for early humans because its conchoidal fracture creates extremely sharp edges for cutting and skinning. It was also used to spark fires.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture patterns and inability to be scratched by a steel knife. Frequently found in riverbeds, gravel pits, and eroding out of limestone cliffs.
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