sedimentary

Banded Chert Pebble

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs scale. Color: Gray, tan, brownish-yellow, and off-white in distinct layered bands. Luster: Dull to sub-vitreous, silky when smooth. Fracture: Conchoidal to sub-conchoidal. Microcrystalline quartz composition.

Hardness: 6
Luster: Dull to sub-vitreous, silky when smooth

Identified July 27, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through chemical accumulation of microcrystalline silica, often precipitated from marine microfossils like radiolaria or diatoms. Later rounded and smoothed through stream or beach water erosion.

Uses & applications

Historically used for making stone tools, arrowheads, and fire-starting flints. Currently popular as decorative landscaping pebbles, aquariums, and rock tumbling specimens.

Geological facts

Banded chert exhibits distinct layers caused by subtle variations in mineral impurities (like iron oxides) or clay content during the original deposition of silica sediment.

Field identification & locations

Identify in the field by its distinct layered banding, high hardness (scratches glass, cannot be scratched by a steel pocket knife), smooth river-worn texture, and waxy or dull finish. Commonly found in riverbeds, gravel pits, and along ocean beaches worldwide.