sedimentary

Weathered chert or flint nodule

Microcrystalline quartz (SiO₂), commonly chalcedony/quartz

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; tan to brown, opaque, earthy to dull/waxy luster, cryptocrystalline structure, and no visible cleavage. The rounded, pitted surface suggests natural weathering or abrasion; pale patches may be silica-rich alteration or cortex.

Identified September 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms by replacement or precipitation of silica in limestone, chalk, or volcanic sediment, generally during the Paleozoic–Cenozoic depending on its host formation. Nodules are later liberated by weathering and rounded in stream or shoreline environments.

Uses & applications

Used historically for cutting tools and fire-starting flints; attractive pieces may be polished for display, cabochons, or lapidary work. Common specimens have modest commercial value.

Geological facts

Chert fractures with a sharp conchoidal edge and was an important prehistoric tool material. The image alone cannot reliably distinguish chert from jasper, silicified limestone, or another brown microcrystalline-silica rock.

Field identification & locations

Common in limestone and chalk regions, river gravels, beaches, and glacial deposits. Test a fresh edge with a steel file or glass—true chert resists scratching glass—while avoiding destructive testing on valuable specimens.