sedimentary

Chert / Flint

Silicon dioxide (SiO2)

Hardness of 7 on the Mohs scale, colors vary from grey, white, yellow, to brown, waxy or vitreous luster, microcrystalline or cryptocrystalline quartz structure, conchoidal fracture, specific gravity around 2.60 to 2.65.

Identified August 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments through the chemical or biochemical precipitation of silica from seawater, often replacing carbonate rocks like limestone during diagenesis. Can range widely in geological age from Precambrian to Cenozoic.

Uses & applications

Historically used for making stone tools, arrowheads, and spark generation in firearms. Today used in abrasives, ceramics, and occasionally as decorative stone or gravel.

Geological facts

Chert and flint are essentially the same material, with 'flint' typically referring to darker varieties found in chalk deposits. Because of its extremely fine grain and conchoidal fracture, it can be chipped to form razor-sharp edges in a process called knapping.

Field identification & locations

Identified easily by its extreme hardness, waxy luster, and distinctive conchoidal fracture (curved, shell-like breakage patterns). Commonly found as nodules or layers within limestone and chalk formations worldwide.