sedimentary

Flint or chert fragment

Microcrystalline quartz (SiO₂), typically chalcedony with possible impurities

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray to olive-brown, dull to waxy luster, very fine-grained cryptocrystalline structure, and conchoidal fracture. It lacks visible cleavage and appears naturally fractured or roughly knapped.

Identified August 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich groundwater replaces or infills sediment, commonly in limestone, or when biogenic silica recrystallizes. It may range from Paleozoic to recent in age, depending on its host formation.

Uses & applications

Used historically for sharp tools, fire-starting, and construction aggregate; attractive pieces may be collected, but this specimen shows limited gem value.

Geological facts

Flint is generally a dark, impure variety of chert; both produce sharp edges when fractured. The smooth curved surfaces and hard, glass-like breaks are diagnostic.

Field identification & locations

Identify it by testing whether it scratches ordinary glass, examining its waxy texture, and looking for conchoidal fractures. Common worldwide in limestone beds, chalk, river gravels, and glacial deposits.