sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Gray, brown, black; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Gray, brown, black
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Gray, brown, black; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed as nodules or beds in sedimentary rocks like limestone or chalk when silica accumulates through chemical precipitation or from the remains of silica-shelled organisms.

Uses & applications

Historically used for stone tools (arrowheads, knives) and starting fires; currently used in construction aggregate and as decorative landscape stone.

Geological facts

Flint was one of the most important minerals for early human technological development because it can be chipped to create razor-sharp edges and generates sparks when struck against steel.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture patterns and ability to scratch glass. Found globally within limestone deposits or as eroded pebbles in riverbeds.