sedimentary

Flint / Chert

Silicon dioxide (Microcrystalline quartz, SiO2)

Hardness: 7 on the Mohs scale. Color: Variable, typically grey, white, brownish, or black. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline/microcrystalline (quartz). Cleavage: None, exhibits conchoidal fracture.

Hardness: 7 on the Mohs scale
Color: Variable, typically grey, white, brownish, or black
Luster: Waxy to vitreous

Identified August 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed diagenetically as nodules within sedimentary rocks such as chalk and marine limestones, through the replacement of calcium carbonate by silica-rich solutions.

Uses & applications

Historically used for making stone tools, weapons, and fire-starting (striking against steel). Today used mainly for ornamental landscaping, grinding pebbles, and occasionally in construction or flintlock firearms.

Geological facts

Flint has been utilized by humans for over two million years due to its ability to fracture with extremely sharp edges (conchoidal fracture). It is chemically identical to quartz and jasper.

Field identification & locations

Easily identified in the field by its waxy luster, smooth water-worn surface (when found as beach pebbles), conchoidal fracture, and ability to scratch glass. Commonly found along chalk cliffs, beaches, and limestone formations worldwide.

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