sedimentary

Banded Chert

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, white, with orange/red iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, tan, white, with orange/red iron staining
Luster: Waxy to dull

Identified March 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from silica-saturated fluids in marine environments. These specimens can range from Precambrian to Cenozoic in age.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges. Modern uses include glassmaking, abrasives, decorative landscaping, and as a semi-precious gemstone in jewelry when it displays interesting patterns.

Geological facts

Chert is so hard it can scratch steel and produce sparks when struck against iron. This specific piece shows 'liesegang rings' or secondary iron oxide staining, which creates the bright orange bands.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. It is common in limestone or dolomite beds globally, particularly in the Midwestern United States and the UK.