sedimentary

Chert

Silicon dioxide (SiO2)

Hardness of 7 on the Mohs scale, typically white, grey, brown, or reddish-brown in color, waxy to vitreous luster, conchoidal fracture, and cryptocrystalline structure.

Identified July 30, 2026More sedimentary →

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Physical properties

Hardness of 7 on the Mohs scale, typically white, grey, brown, or reddish-brown in color, waxy to vitreous luster, conchoidal fracture, and cryptocrystalline structure.

Formation & geological history

Formed by the chemical precipitation of silica from aqueous solutions or through the accumulation of siliceous remains of marine organisms such as diatoms and radiolarians in deep marine environments over millions of years.

Uses & applications

Historically used by early humans for making stone tools such as arrowheads and knives due to its conchoidal fracture; occasionally used in ornamental applications or landscaping.

Geological facts

Chert that occurs in limestone or chalk deposits is commonly known as flint. Because of its conchoidal fracture, it breaks into very sharp edges, making it ideal for primitive weaponry and tools.

Field identification & locations

Can be identified in the field by its extreme hardness (scratches glass easily), waxy luster, and characteristic conchoidal fracture. Commonly found in limestone and chalk formations worldwide.