sedimentary

Chert (Flint)

Microcrystalline quartz (SiO2)

Hardness of 7 on the Mohs scale, typically white, gray, or brown in color, waxy to dull luster, cryptocrystalline structure, conchoidal fracture with no true cleavage, specific gravity of 2.60 to 2.65.

Identified August 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via chemical and biochemical precipitation in marine environments, often replacing calcium carbonate in limestone or chalk during diagenesis over millions of years.

Uses & applications

Historically used extensively by ancient humans for making stone tools and weapons (arrowheads, spear points, blades) due to its sharp conchoidal fracture. Also used historically to strike sparks for fire-starting.

Geological facts

Chert and flint are chemically identical forms of microcrystalline quartz, though 'flint' is often reserved for darker varieties found in chalk formations. Its extreme durability allows it to survive in the geological record long after surrounding host rocks erode.

Field identification & locations

Easily identified in the field by its characteristic conchoidal fracture (producing very sharp, glass-like edges) and high hardness that scratches glass. Commonly found as nodules within limestone or chalk deposits worldwide.