sedimentary

Flint or chert

Microcrystalline quartz (SiO₂), commonly chalcedony with possible impurities

AI-generated identification · may be incorrect

Dark gray-brown, opaque, waxy to dull luster, very fine-grained and massive; conchoidal fracture and no visible cleavage. Mohs hardness is about 6.5–7; the irregular pale marks may be weathering, quartz veins, or impact scars.

Identified August 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills cavities in limestone and other sediments, often during diagenesis. It can range from Paleozoic to younger ages depending on its host formation.

Uses & applications

Historically used for sharp tools, arrowheads, and fire-starting; today it is mainly collected, studied, or used decoratively. This rough, weathered piece has little commercial value.

Geological facts

Its sharp conchoidal edges are characteristic of flint/chert, though the pictured specimen may also be a dark siliceous rock such as hornfels or weathered quartzite. Precise identification requires a fresh fracture and host-rock context.

Field identification & locations

Common in limestone regions, river gravels, and glacial deposits worldwide; notable sources include England, France, Texas, Kansas, and the Great Lakes region. Test a fresh edge with a steel file or glass—true chert typically scratches glass.