sedimentary

Flint / Chert

Silicon dioxide (SiO2)

Hardness of 7 on the Mohs scale, dark brown/black/grey color, waxy to vitreous luster, microcrystalline (cryptocrystalline) quartz structure, exhibits conchoidal fracture with sharp edges, specific gravity around 2.60 to 2.65.

Identified July 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through chemical sedimentary processes, typically by the replacement of calcium carbonate in limestone or chalk by silica-rich solutions, 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 blades due to its sharp conchoidal fracture. Also used for fire-making (striking sparks) and historically in flintlock firearms.

Geological facts

Flint and chert are essentially the same material, though 'flint' typically refers to the dark varieties found in chalk formations. It was one of the earliest materials manipulated by early humans for technology.

Field identification & locations

Easily identified in the field by its waxy luster, smooth nodular surfaces often with a white chalky cortex, and sharp conchoidal fracture edges. Found worldwide within chalk or limestone deposits.