$Flint (chert), likely a worked or fractured nodule (Microcrystalline quartz/chalcedony (SiO₂)) — sedimentary$

sedimentary

Flint (chert), likely a worked or fractured nodule

Microcrystalline quartz/chalcedony (SiO₂)

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; dark gray to brown, with dull to waxy luster and a pale weathered cortex. It is cryptocrystalline, lacks cleavage, has conchoidal fracture, and typically weighs about 2.5–2.7 g/cm³.

Identified August 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Flint forms by replacement of carbonate sediment, commonly from biogenic silica in chalk or limestone, during diagenesis. Its age depends on the host formation; the specimen’s broken, sharp-edged surface may indicate human knapping or natural fracture.

Uses & applications

Historically used for stone tools, fire-starting, and weapons; today it is mainly a teaching or collecting specimen, with limited aggregate use.

Geological facts

The smooth curved break surfaces and very fine grain are diagnostic of chert/flint. Dark coloration commonly comes from organic matter, iron, or other trace impurities.

Field identification & locations

Identify it by testing for glass-like conchoidal fracture, lack of visible grains, and inability to scratch it with a steel knife (though it may scratch glass). Common in chalk and limestone regions worldwide, including England, France, the U.S. Midwest, and Texas.