sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Gray, brown, or black; Luster: Waxy to dull; Structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8

Hardness: 6
Color: Gray, brown, or black
Luster: Waxy to dull

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Gray, brown, or black; Luster: Waxy to dull; Structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments; commonly found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and starting fires; currently used as a decorative stone, in construction aggregate, and occasionally in jewelry.

Geological facts

Because of its conchoidal fracture, it can be chipped to form extremely sharp edges. It was one of the most important minerals for prehistoric humans to create tools like arrowheads and knives.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel) and curved, glass-like fracture surfaces. Often found as rounded nodules in sedimentary rock layers.