sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

Hardness: 7 on Mohs scale; Color: Tan, yellow, or light brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, yellow, or light brown
Luster: Waxy to dull

Identified June 23, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, yellow, or light brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine environments; age varies from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools (flint knapping). Modern use in road construction and as decorative garden stones.

Geological facts

Chert is so hard it can scratch glass and steel. It was one of the most important materials for early humans to create spearheads and arrowheads due to its sharp edges when broken.

Field identification & locations

Identify by its extreme hardness, waxy texture, and conchoidal (shell-like) fracture patterns. Found globally in limestone formations or as river pebbles.