sedimentary

Chert

Cryptocrystalline Silica (SiO2)

Hardness: 7 on Mohs scale; Color: Rusty brown/tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Rusty brown/tan
Luster: Waxy to dull

Identified June 22, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Rusty brown/tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed primarily by the accumulation of siliceous remains of organisms like diatoms or radiolarians, or through chemical precipitation in marine environments. This specimen shows oxidation typical of weathered surface deposits.

Uses & applications

Historically used for stone tools and arrowheads; currently used in construction aggregate, road surfacing, and as a polishing abrasive.

Geological facts

Chert is so hard it can scratch glass and steel. It was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges.

Field identification & locations

Field identification focuses on its extreme hardness, waxy texture, and conchoidal (shell-like) fracture patterns. It is found globally in limestone and chalk beds.