sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Gray, black, white, tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (shows conchoidal fracture); Specific gravity: 2.65

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

Identified June 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or by chemical precipitation from silica-rich groundwater. Found in sedimentary environments, often as nodules in limestone or chalk.

Uses & applications

Historically used for stone tools and fire-starting; currently used in construction aggregate, road surfacing, and as a decorative stone in jewelry or lapidary arts.

Geological facts

Flint was one of the most important materials in the Stone Age for creating sharp-edged tools like arrowheads and knives because of the predictable way it breaks (conchoidal fracture).

Field identification & locations

Identify by its waxy luster, extreme hardness (it will scratch glass), and the curved, shell-like (conchoidal) patterns on broken surfaces. Often found in riverbeds or within limestone outcrops.