sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, white, and dark charcoal banding; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 6
Color: Gray, tan, white, and dark charcoal banding
Luster: Waxy to dull

Identified February 20, 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 in marine environments. Banding represents seasonal or environmental changes during deposition, often dating back to the Paleozoic or Mesozoic eras.

Uses & applications

Historically used for stone tools and arrowheads due to sharp edges; currently used for decorative landscaping, jewelry (when polished), and as a component in road base construction.

Geological facts

Chert is so hard it can strike sparks against steel, a property that led to its use in flintlock firearms. The specific rounded shape of this specimen suggests it was tumbled by water in a river or stream for a long duration.

Field identification & locations

Identify in the field by its smooth, waxy texture and inability to be scratched by a steel knife. It is extremely common in gravel pits and along riverbeds across North America and Europe.