sedimentary

Chert (Flint)

Chert (Silicon Dioxide, SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, white, or brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Hardness: 7 on Mohs scale
Color: Gray, tan, white, or brown
Luster: Waxy to dull

Identified May 27, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains or the chemical precipitation of silica in sedimentary basins, often occurring as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and fire-starting; currently used as road aggregate, in jewelry (as jasper or agate varieties), and for flintlock firearms.

Geological facts

Flint is a variety of chert that was the primary material for the Stone Age technology due to its ability to chip into sharp edges. It produces sparks when struck against steel.

Field identification & locations

Identify by its 'waxy' texture and sharp, curved (conchoidal) edges when broken. It is harder than steel and will scratch glass. Common in river beds and chalk cliffs.