sedimentary

Brown flint or chert pebble

Microcrystalline quartz (SiO₂), commonly with iron-oxide staining

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque brown to ochre, dull-to-waxy luster, very fine-grained cryptocrystalline structure, and no visible cleavage. The rounded, smooth surface indicates water abrasion, while cracks and pits are natural weathering features.

Identified September 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich sediment or biogenic silica is chemically replaced and lithified, often within limestone or chalk; its age depends on the host formation. This specimen was likely rounded in a river, beach, or glacial deposit.

Uses & applications

Used historically for sharp tools and fire-starting; attractive pieces are collected or used as lapidary material, though this example appears mainly ornamental.

Geological facts

Freshly broken chert commonly shows a curved, conchoidal fracture and sharp edges. Brown coloration generally comes from iron oxides or hydroxides rather than the quartz itself.

Field identification & locations

Look for extreme hardness, inability to scratch with a steel knife, fine texture, and conchoidal fracture; it commonly occurs as nodules or pebbles in limestone regions, river gravels, and beaches.