sedimentary

Flint / Chert

Microcrystalline quartz (SiO2)

Hardness of 7 on the Mohs scale. Colors range from dark grey, blue, black, to white and brown due to impurities. It exhibits a waxy to vitreous luster and typically has a conchoidal fracture with sharp edges. It is cryptocrystalline, meaning the crystals are too small to see without high magnification.

Identified August 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as nodules or beds in sedimentary rocks, such as chalk and limestone, through the replacement of calcium carbonate by silica-rich solutions in marine environments over millions of years.

Uses & applications

Historically used for making stone tools, arrowheads, and fire-starting (striking against steel). Today used in abrasives, road construction, and occasionally ornamental carvings or lapidary work.

Geological facts

Flint is famous for its ability to produce sharp flakes when struck, making it one of the most important materials in human technological development during the Stone Age. It produces sparks when struck against iron pyrite or steel.

Field identification & locations

Can be identified in the field by its smooth, weathered outer cortex, conchoidal fracture showing sharp edges, waxy luster, and high hardness that scratches glass easily. Commonly found in chalk deposits and glacial till.