sedimentary

Chert

Chert (SiO2)

Hardness: 7 Mohs scale; Color: Tan, brown, or variegated; Luster: Waxy to dull; Crystal structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs scale
Color: Tan, brown, or variegated
Luster: Waxy to dull

Identified June 23, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Tan, brown, or variegated; Luster: Waxy to dull; Crystal structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed primarily by the accumulation of siliceous remains of microscopic organisms like diatoms or radiolarians, or through chemical precipitation in marine environments. They range from Precambrian to Holocene in age.

Uses & applications

Historically used for stone tools like arrowheads due to sharp edges; currently used for decorative stone, gravel in road construction, and occasionally as jewelry in the form of jasper.

Geological facts

Chert has been used by humans for millions of years to create fires and weapons because of its ability to fracture into sharp edges and produce sparks when struck against iron or steel.

Field identification & locations

Identified by its extreme hardness (cannot be scratched by a steel knife), waxy appearance, and smooth, curved (conchoidal) fractures. Found in nodules within limestone or as bedded layers.