sedimentary

Iron-stained chert or flint nodule

Microcrystalline quartz (SiO₂), likely chert with limonite/goethite staining

AI-generated identification · may be incorrect

Hardness about 7 Mohs; brown, tan, and cream with a dull to waxy luster, very fine-grained texture, irregular conchoidal-fracture surfaces, and no visible cleavage. The pale band may be silica-rich material or weathered carbonate/chalk inclusion.

Identified August 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by precipitation or replacement of silica in sedimentary beds, commonly as a concretion or nodule; iron oxides produced the brown coloration during weathering. Exact age cannot be determined from the photograph.

Uses & applications

Used historically for sharp tools and fire-starting; attractive pieces are collected, but this specimen is generally not gem-quality or valuable for construction.

Geological facts

Chert can resemble jasper, petrified wood, or iron-rich quartzite. A fresh broken edge should be glassy and sharp, and it should scratch ordinary glass.

Field identification & locations

Common in limestone, chalk, and marine sedimentary formations worldwide, including regions of England, France, the Great Plains, and the Great Lakes. Confirm with a glass-scratch test, streak test, and close inspection for conchoidal fracture; avoid destructive testing on valuable specimens.