sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 Mohs; Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline) quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs
Color: Gray, tan, or brown
Luster: Waxy to dull

Identified May 31, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline) quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments; age varies from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools and starting fires; currently used as a road aggregate, in jewelry as semi-precious stones (jaspers), and as an abrasive.

Geological facts

Chert breaks with a conchoidal fracture, creating extremely sharp edges, which made it the primary material for prehistoric arrowheads and spear points.

Field identification & locations

Look for a microcrystalline texture that feels smooth or waxy, and look for curved, glass-like shell-shaped fractures. Commonly found in limestone or chalk beds.