sedimentary

Flint

SiO2 (Cryptocrystalline Quartz / Chert)

Hardness of 7 on the Mohs scale, colors range from dark gray, brown, to black often with a lighter weathering cortex, waxy to vitreous luster, microcrystalline structure with conchoidal fracture, and no cleavage.

Identified August 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed chemically or biochemically in marine environments, typically through the replacement of calcium carbonate in chalk or limestone by silica-rich solutions during diagenesis. Geological age generally ranges from Cretaceous to Jurassic periods.

Uses & applications

Historically used for prehistoric stone tools, arrowheads, and fire-making (striking against steel). Today used as decorative aggregate, in specialized grinding mills, and occasionally in construction.

Geological facts

Flint is a variety of chert specifically associated with chalk formations. Due to its conchoidal fracture, it can be chipped to form extremely sharp edges, making it one of the most important materials for early human technological development.

Field identification & locations

Easily identified in the field by its dark color, conchoidal fracture showing sharp edges, waxy luster, and often a white or cream-colored chalky outer rind. Commonly found embedded in chalk cliffs or as rolled pebbles on beaches.