sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs); Color: Tan, beige, and white bands; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 – 2.7.

Hardness: 7 (Mohs)
Color: Tan, beige, and white bands
Luster: Waxy to dull

Identified April 3, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs); Color: Tan, beige, and white bands; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 – 2.7.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. The banding represents changes in sediment supply or oxygen levels during deposition.

Uses & applications

Historically used for stone tools (arrowheads). Today used as decorative landscaping stones, aquarium gravel, and occasionally for lapidary work (cabs).

Geological facts

Chert is so hard it can strike sparks against steel. Banded varieties are often found as 'river stones' because their hardness allows them to survive long-distance transport in water.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by steel), waxy texture, and smooth, shell-like (conchoidal) fractures. Often found in riverbeds or coastal areas.