sedimentary

Flint

Silicon dioxide (SiO2) microcrystalline quartz

Hardness: 7 on the Mohs scale. Color: various shades of grey, blue, black, or dark brown. Luster: waxy to vitreous on fresh surfaces, dull on cortex. Crystal structure: microcrystalline / cryptocrystalline (chalcedony). Cleavage: none, exhibits conchoidal fracture. Specific gravity: 2.60 to 2.65.

Hardness: 7 on the Mohs scale
Color: various shades of grey, blue, black, or dark brown
Luster: waxy to vitreous on fresh surfaces, dull on cortex

Identified August 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the replacement of calcium carbonate by silica-rich solutions in chalk or limestone formations during the Cretaceous period.

Uses & applications

Historically used for making stone tools, weapons, and fire-striking (flint and steel); currently used in decorative landscaping, construction aggregate, and occasionally in lapidary arts.

Geological facts

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

Field identification & locations

Easily identified by its characteristic conchoidal fracture, smooth water-worn exterior when found on beaches or rivers, and high hardness capable of scratching glass.

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