sedimentary

Banded Chert

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs). Color: Variegated black, grey, and ochre/tan bands. Luster: Waxy to dull. Crystal Structure: Microcrystalline/Cryptocrystalline quartz. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Hardness: 6
Color: Variegated black, grey, and ochre/tan bands
Luster: Waxy to dull

Identified June 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (radiolarites/diatoms) or chemical precipitation in marine environments. The banding typically represents seasonal or cyclic depositional changes. Found in Precambrian to Cenozoic strata.

Uses & applications

Historically used for stone tools and arrowheads; currently used in jewelry (as tumbled stones), lapidary projects, and road construction aggregate.

Geological facts

Banded chert and its close relative, jasper, are among the earliest materials used by humans for toolmaking due to their predictability when fractured. Some banded iron formations containing chert date back over 2 billion years.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife), waxy smooth texture, and smooth, curved conchoidal fractures. Commonly found in riverbeds, shoreline gravels, and limestone outcrops.