sedimentary

Tumbled chert or flint pebble

Microcrystalline quartz (SiO₂), likely chert/flint

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; tan to brown, waxy-to-dull luster, very fine-grained cryptocrystalline structure, no visible cleavage, and conchoidal fracture. The smooth surface and rounded shape indicate natural water wear or tumbling; exact identification is limited by the photograph.

Identified September 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich fluids replace or cement sediments, commonly in limestone or chalk, from Precambrian through modern geological settings. This specimen was later rounded by erosion or artificial tumbling.

Uses & applications

Used historically for sharp tools and fire-starting; attractive pieces are sold as lapidary material, cabochons, carvings, and polished curios. It has little construction value as an individual pebble.

Geological facts

A steel file or quartz crystal should not easily scratch it, while chert can scratch ordinary glass. Flint is a dark, often chalk-associated variety of chert; this brown material is more generally called chert.

Field identification & locations

Common in sedimentary terrains, river gravels, beaches, and glacial deposits worldwide; inspect for a glassy waxy surface, conchoidal chips, and absence of visible grains. A streak test is usually white.