sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Grey, blue-grey, tan, and rusty orange (iron staining); Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Hardness: 7 Mohs scale
Color: Grey, blue-grey, tan, and rusty orange (iron staining)
Luster: Waxy to vitreous

Identified July 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from groundwater or as a replacement of carbonate minerals in sedimentary sequences. Often occurs as nodules or beds in limestone and chalk, dating from various eras including the Cretaceous.

Uses & applications

Historically used for stone tools and weapons due to sharp edges when fractured. Modern uses include abrasives, road construction, and as flint for fire-starting in survival kits.

Geological facts

Chert has been used by humans for millions of years to create arrowheads and scrapers. Its ability to produce sparks when struck against steel made it essential for flintlock firearms.

Field identification & locations

Identify in the field by its characteristic smooth, bowl-shaped (conchoidal) fractures and its ability to scratch glass. Commonly found in limestone outcrops, riverbeds, and chalk cliffs.