sedimentary

Tumbled chert or flint pebble

Microcrystalline quartz (SiO₂), likely chert; exact variety uncertain from the image

AI-generated identification · may be incorrect

Hardness ~6.5–7 Mohs; opaque tan-brown, matte to slightly waxy luster, very fine-grained cryptocrystalline structure, no visible cleavage, and conchoidal-fracture tendency. The rounded shape indicates natural water wear or tumbling.

Identified August 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica from microscopic marine organisms or groundwater replaces sediment, commonly in limestone; ages range from Precambrian to recent. This specimen was likely transported and rounded in a river, beach, or gravel deposit.

Uses & applications

Used historically for sharp tools and fire-starting; attractive pieces are sold as tumbled stones, craft material, or low-cost cabochons.

Geological facts

Chert and flint are chemically similar varieties of microcrystalline quartz; darker flint commonly contains organic matter or impurities. The pale brown color can result from iron oxides and other sedimentary impurities.

Field identification & locations

Identify it by its uniform fine texture, high hardness, earthy/waxy surface, and possible sharp conchoidal break; it should scratch glass but not a steel knife easily. Common in limestone regions, river gravels, and glacial deposits.