sedimentary

Chert / Flint

Microcrystalline quartz (SiO2)

Hardness of 7 on the Mohs scale, colors vary from grey, brown, white to black, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with no true cleavage, specific gravity of 2.60 to 2.65.

Identified July 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the replacement of calcium carbonate by silica-rich solutions in sedimentary environments like chalk or limestone, or through the accumulation of siliceous skeletal remains of marine organisms over millions of years.

Uses & applications

Historically used for making stone tools, arrowheads, and fire-starting (flint and steel); currently used in abrasives, road aggregate, and occasionally in ornamental stonework or lapidary arts.

Geological facts

Chert and flint are chemically identical; the term 'flint' is often used specifically for darker varieties found in chalk formations. It was one of the earliest materials manipulated by early humans to create advanced tools.

Field identification & locations

Easily identifiable in the field by its distinct conchoidal fracture (smooth, curved breakage surfaces) and extreme hardness that easily scratches glass. Commonly found within sedimentary limestone and chalk beds worldwide.