sedimentary

Flint

Microcrystalline quartz (SiO2)

Hardness of 7 on the Mohs scale; gray, brown, or black color; waxy to vitreous luster; cryptocrystalline structure; conchoidal fracture with very sharp edges; specific gravity around 2.60.

Identified July 30, 2026More sedimentary →

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Physical properties

Hardness of 7 on the Mohs scale; gray, brown, or black color; waxy to vitreous luster; cryptocrystalline structure; conchoidal fracture with very sharp edges; specific gravity around 2.60.

Formation & geological history

Formed through the chemical replacement of limestone or chalk by silica-rich solutions or the accumulation of siliceous skeletal remains of marine organisms in deep marine environments during the Cretaceous and other periods.

Uses & applications

Historically used for making stone tools, weapons, and arrowheads due to its conchoidal fracture; later used for fire-starting with steel and in flintlock firearms; occasionally used in ornamental items.

Geological facts

Flint is virtually identical to chert, though the term flint is often specifically reserved for the dark variety found in chalk formations. It was one of the earliest materials mastered by early humans for toolmaking.

Field identification & locations

Easily identified in the field by its distinct conchoidal fracture, sharp edges, waxy luster, and occurrence as nodules or layers within chalk or limestone. Found worldwide, particularly in regions with extensive chalk deposits such as southeastern England, France, and parts of North America.