sedimentary

Flint or chert

Microcrystalline quartz (SiO₂), commonly with chalcedony and minor impurities

AI-generated identification · may be incorrect

Typically dark gray to black, very fine-grained, opaque, with a waxy to dull luster and conchoidal fracture; hardness about 6.5–7 Mohs, no cleavage, and specific gravity near 2.6. The smooth curved break and sharp edge are characteristic.

Identified September 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms by replacement or accumulation of silica in sedimentary rocks, especially limestone and chalk, commonly during diagenesis. It may range from Paleozoic to Cenozoic in age, depending on its host formation.

Uses & applications

Historically used for flaked stone tools, fire-starting, and projectile points; today it is mainly a teaching, lapidary, and collecting material. It has limited industrial use compared with higher-purity quartz.

Geological facts

Flint is generally a dense, dark variety of chert, while lighter or multicolored examples are usually called chert. Its conchoidal fracture can produce extremely sharp cutting edges.

Field identification & locations

Identify it by testing for glass-like conchoidal fracture, lack of visible grains, and resistance to scratching glass. Common occurrences include limestone and chalk regions worldwide, including England, France, the Great Lakes, and Texas.