sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs. Color: usually brownish-black, grey, or dark tan. Luster: Vitreous to waxy. Structure: Microcrystalline/Cryptocrystalline. Features: Conchoidal fracture with sharp edges.

Hardness: 6
Color: usually brownish-black, grey, or dark tan
Luster: Vitreous to waxy

Identified July 12, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs. Color: usually brownish-black, grey, or dark tan. Luster: Vitreous to waxy. Structure: Microcrystalline/Cryptocrystalline. Features: Conchoidal fracture with sharp edges.

Formation & geological history

Formed as nodules or beds in sedimentary rocks (like limestone) through the chemical precipitation of silica, often from the remains of microscopic organisms like diatoms or radiolarians.

Uses & applications

Historically used for stone tools and weapons (arrowheads, scrapers) and to strike fire. Today used as a road aggregate, in jewelry as jasper/agate variants, and as a decorative stone.

Geological facts

Flint was a vital survival resource for prehistoric humans due to its ability to be knapped into extremely sharp tools and its sparking properties when struck against steel or iron pyrites.

Field identification & locations

Identify in the field by its smooth, waxy texture and curved, glass-like 'conchoidal' fractures. Found globally in chalk and limestone deposits. Highly prized by flint-knapping hobbyists.