sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Black with white/grey cortex; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.7.

Hardness: 7 (Mohs scale)
Color: Black with white/grey cortex
Luster: Waxy to vitreous

Identified March 19, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Black with white/grey cortex; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 – 2.7.

Formation & geological history

Formed via chemical precipitation of silica-rich fluids or replacement of calcium carbonate in sedimentary environments like limestone or chalk. Often associated with Cretaceous or Paleozoic eras.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Currently used in road aggregates, concrete, and as a raw material for silicon-based products.

Geological facts

Flint was the primary material for the Stone Age technology due to its ability to produce razor-sharp edges. It produces sparks when struck against steel, which was once the standard mechanism for firearms (flintlocks).

Field identification & locations

Identify by its waxy texture and characteristic curved, shell-like (conchoidal) fractures. Often found as nodules within limestone or as river pebbles. Collectors look for pieces with high-contrast color bands or fossils.