sedimentary

Chert (often called Flint)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, tan, brown, or white; Luster: Dull to waxy; Structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, tan, brown, or white
Luster: Dull to waxy

Identified June 24, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, brown, or white; Luster: Dull to waxy; Structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed as nodules or layered deposits in limestone or chalk through the accumulation of silica-rich organic remains or chemical precipitation. Primarily found in marine sedimentary layers of various ages.

Uses & applications

Historically used for stone tools (arrowheads, knives) and striking fire; currently used as a road aggregate, in glass making, and by flintknapping hobbyists.

Geological facts

Chert breaks with a conchoidal fracture, creating sharp edges that are sharper than a steel scalpel. It was one of the most important resources for prehistoric humans.

Field identification & locations

Identify by its extremely fine grain (can't see crystals), waxy feel, and the way it breaks into curved, glass-like shards. Often found in creek beds or eroding out of limestone cliffs.