sedimentary

Flint

SiO2 (Microcrystalline Quartz / Chert)

Hardness: 7 on the Mohs scale. Color: Dark grey, brown, or black with a white or grey weathered cortex. Luster: Vitreous to waxy. Crystal structure: Cryptocrystalline / Microfibrous quartz. Cleavage: None, exhibits distinctive conchoidal fracture. Specific gravity: 2.60 to 2.65.

Hardness: 7 on the Mohs scale
Luster: Vitreous to waxy

Identified August 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as nodules or masses in sedimentary rocks such as chalk and limestone through the replacement of calcium carbonate by silica-rich solutions during the Cretaceous period.

Uses & applications

Historically used for making stone tools, weapons, and fire-starting strikers. Today used in decorative gravel, abrasive blasting, and historically in building construction.

Geological facts

Flint was one of the earliest materials manipulated by early humans to create sharp cutting edges, arrowheads, and hand axes due to its predictable conchoidal fracture.

Field identification & locations

Easily identified in the field by its dark glassy interior, smooth conchoidal fracture scars, and typically chalky outer cortex. Commonly found along chalk cliffs and beaches in regions like Southern England, France, and parts of North America.