sedimentary

Chert (Flint)

Chert (Silicon Dioxide, SiO2)

Hardness: 7 on Mohs scale; Color: Gray, brown, or tan with waxy/dull luster; Crystal structure: Microcrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, brown, or tan with waxy/dull luster

Identified June 20, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, brown, or tan with waxy/dull luster; Crystal structure: Microcrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical precipitation of silica in marine or groundwater environments. It typically occurs as nodules or layers within limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges. Modern uses include abrasives, road construction material, and occasionally as semi-precious gemstones in jewelry (as jasper or agate varieties).

Geological facts

Because it sparks when struck against steel, it was the primary material for flintlock firearms. It was one of the most important trade commodities of the prehistoric world.

Field identification & locations

Identify in the field by its very smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass easily. It is commonly found in sedimentary basins and riverbeds globally.