sedimentary

Chert

Chert (SiO2)

Hardness: 7 Mohs scale; Color: Cream, tan, yellowish-brown; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs scale
Color: Cream, tan, yellowish-brown
Luster: Dull to waxy

Identified June 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from groundwater or the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) in sedimentary environments. Can be found in nodules or bedded layers.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) because of its sharp conchoidal fracture. Modern uses include road surfacing, decorative gravel, and as a raw material in some ceramic glazes.

Geological facts

Chert is essentially the same mineral as jasper, flint, and agate, distinguished primarily by its color and opacity. It has been one of the most important minerals for human technology during the Stone Age.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and waxy, smooth texture compared to surrounding limestone. Look for conchoidal (shell-like) fracture patterns on broken edges.