sedimentary

Banded Chert

Silicon dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, and white bands; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 6
Color: Gray, tan, and white bands
Luster: Dull to waxy

Identified June 26, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, and white bands; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolarians or diatoms) or through chemical precipitation in marine or groundwater environments. These bands represent variations in mineral content or sediment deposition during formation.

Uses & applications

Historically used for stone tools and weapons due to its conchoidal fracture. Today used as an abrasive, in landscaping, and as a collector's specimen.

Geological facts

Chert is so hard it can strike sparks against steel. The banding in this specimen is likely due to rhythmic deposition of silica-rich layers in a prehistoric seabed.

Field identification & locations

Identify by its hardness (cannot be scratched by a steel knife) and smooth, shell-like (conchoidal) fracture surfaces. Commonly found in limestone and dolomite formations or as pebbles in stream beds.