sedimentary

Chert (and Flint)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs; Color: Grey, blue-grey, white; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs
Color: Grey, blue-grey, white
Luster: Waxy to dull

Identified March 24, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Grey, blue-grey, white; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in sedimentary basins. Most commonly found in limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons due to sharp edges; currently used as a flux in glassmaking, construction aggregate, and for decorative lapidary work.

Geological facts

Chert was one of the most important materials in human prehistory for crafting arrowheads and spear tips because its conchoidal fracture produces edges sharper than a surgical scalpel.

Field identification & locations

Identify by its extremely sharp, curved edges when broken and the fact that it cannot be scratched by a steel knife. It will also spark when struck against steel. Found globally in nodules or layered beds within carbonate rocks.