sedimentary

Chert (Flint)

Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, brown, black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

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

Identified May 30, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, brown, black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in sedimentary basins, often replacing limestone or chalk. Commonly found in Upper Cretaceous formations.

Uses & applications

Historically used for stone tools and starting fires (flintlocks). Currently used in road construction, as a gemstone (Jasper varieties), and for making glass or ceramics.

Geological facts

Flint was the primary material for the Stone Age tool industry due to its ability to split into razor-sharp edges. It is chemically very stable and can survive long periods of weathering.

Field identification & locations

Identify by its waxy luster, smooth conchoidal (shell-like) fractures, and its ability to scratch glass. It often occurs as nodules within limestone or chalk beds.