sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs; Color: Gray, tan, brown; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs
Color: Gray, tan, brown
Luster: Dull to waxy

Identified June 10, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Gray, tan, brown; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed by the precipitation of silica in sedimentary environments, often replacing carbonate material or accumulating from the remains of silica-shelled organisms like diatoms and radiolarians around 100-500 million years ago.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used in jewelry (as jasper), as road aggregate, and for starting fires (flint).

Geological facts

Chert has been used by humans for over 2 million years. It is extremely chemically stable and resistant to weathering, which is why it is often found as smooth nodules in riverbeds.

Field identification & locations

Identify by its conchoidal (shell-like) fracture, ability to scratch glass, and waxy luster. Common in limestone and chalk beds globally, especially in regions like the UK and the Midwestern USA.