sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

Hardness: 7 on Mohs scale; Color: Brownish-tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Hardness: 7 on Mohs scale
Color: Brownish-tan
Luster: Waxy to dull

Identified May 28, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brownish-tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Formation & geological history

Formed primarily by the accumulation of siliceous remains of marine organisms (like diatoms or radiolaria) or by chemical precipitation of silica in groundwater.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its conchoidal fracture. Today used as road surfacing, in construction aggregates, and occasionally as decorative stones.

Geological facts

Chert was one of the most important minerals for early humans because its sharp edges when broken were essential for hunting and survival tools.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in limestone beds as nodules.