sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

Hardness: 7 Mohs; Color: Tan, beige, grey, or yellowish; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5–2.8

Hardness: 7 Mohs
Color: Tan, beige, grey, or yellowish
Luster: Waxy to dull

Identified June 7, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Tan, beige, grey, or yellowish; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5–2.8

Formation & geological history

Formed from the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or through chemical precipitation in sedimentary environments. Common in marine limestone and dolomite formations across various geological ages.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges; used today as a decorative stone, road ballast, and in some industrial grinding processes.

Geological facts

Chert has been one of the most important minerals in human history, used since the Paleolithic era to create arrowheads, scrapers, and blades. Sparking chert against steel was an early method for starting fires.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy appearance, and conchoidal (shell-like) fracture patterns. Frequently found as nodules within limestone or as bedded layers.