sedimentary

Chert (Flint)

Chert (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, white, and translucent; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline) quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, white, and translucent
Luster: Waxy to dull

Identified June 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of silica from groundwater or the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) in sedimentary environments. Common in limestone and chalk beds.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) and fire-starting. Currently used in road construction as aggregate and occasionally as a gemstone or in decorative landscaping.

Geological facts

Flint is a variety of chert that was essential to prehistoric humans for tool-making because it fractures predictably into extremely sharp edges. It can produce sparks when struck against iron or steel.

Field identification & locations

Identify in the field by its sharp, curved (conchoidal) edges and its ability to scratch glass. It is commonly found in riverbeds, coastal chalk cliffs, and as nodules within limestone outcrops.