sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, tan, gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8.

Hardness: 6
Color: Brown, tan, gray
Luster: Waxy to dull

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, tan, gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in sedimentary environments. Common in marine limestone and chalk deposits.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges; currently used for road surfacing, flintlocks, and as a decorative landscaping stone.

Geological facts

Because it breaks with a conchoidal fracture, it creates extremely sharp edges; ancient humans used it for arrowheads and scrapers. It can strike sparks against steel to start fires.

Field identification & locations

Identify by its waxy texture, smoothness, and the distinctive curved (shell-like) chips on its surface. Often found as rounded nodules on beaches or embedded in limestone cliffs.