sedimentary

Likely weathered flint or chert fragment

Cryptocrystalline quartz (SiO₂), possibly siliceous chert/flint

AI-generated identification · may be incorrect

Dark gray-brown, dull to subtly waxy luster, very fine-grained with no visible crystals; Mohs hardness about 6.5–7, conchoidal fracture, and no cleavage. The surface appears naturally weathered or possibly lightly worked.

Identified August 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when microcrystalline quartz replaces silica-rich sediment or accumulates as nodules in limestone, commonly during the Paleozoic–Cenozoic eras. Flint is a dark variety often associated with marine chalk and limestone.

Uses & applications

Historically used for sharp tools, scrapers, and fire-starting; attractive polished pieces are used decoratively, but this specimen has little commercial gemstone value.

Geological facts

Its sharp conchoidal edges and glasslike fracture are diagnostic of quartz-rich chert. Dark coloration commonly comes from organic matter, iron, or manganese impurities.

Field identification & locations

Look for a smooth waxy surface, lack of visible grains, high hardness, and conchoidal fracture; it should scratch glass but not be scratched by a steel knife. Common in limestone, chalk, gravel, and glacial deposits worldwide.