sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Tan, brown, gray; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 (Mohs scale)
Color: Tan, brown, gray
Luster: Waxy to dull

Identified July 20, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Tan, brown, gray; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed as nodules or layered deposits in limestone or chalk through the accumulation of silica-rich organic remains or chemical precipitation. Found in marine sedimentary environments worldwide.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Currently used in road surfacing, as an abrasive, and sometimes for lapidary work.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges, ideal for arrowheads and scrapers. Flint is a variety of chert commonly associated with chalk.

Field identification & locations

Identify by its waxy texture, high hardness (it will scratch glass), and curved, shell-like (conchoidal) fractures. Often found in gravel beds or weathered out of limestone outcrops.