sedimentary

Chert or flint nodule

Microcrystalline quartz (SiO₂), likely chalcedony-rich chert

AI-generated identification · may be incorrect

Typically hardness 6.5–7 Mohs, waxy to dull luster, opaque cream-to-tan color, and conchoidal fracture; it lacks visible crystal faces and has no cleavage. The specimen appears weathered and possibly lightly coated with whitish surface material.

Identified August 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica precipitates or replaces sediment, commonly as nodules in limestone or chalk; the exact geological age cannot be determined from the photograph. Chert occurs in marine sedimentary formations from Precambrian through recent ages.

Uses & applications

Used historically for sharp tools and fire-starting, and today as a collector specimen, aggregate, and occasional decorative stone; fine flint may be knapped. It has little jewelry value unless strongly colored or patterned.

Geological facts

Chert is chemically similar to quartz but consists of microscopic quartz and chalcedony crystals. A fresh broken edge may be translucent and glassy, while weathered surfaces become pale and chalky.

Field identification & locations

Common in limestone, chalk, and gravel deposits worldwide, including the Great Lakes, Texas, Kansas, England, and France. Test cautiously with a steel file or glass: genuine chert resists scratching and may produce a sharp conchoidal edge.