sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs scale; Color: Multi-colored bands (grey, tan, brown); Luster: Waxy to vitreous when wet or polished; Structure: Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.65

Hardness: 7 Mohs scale
Color: Multi-colored bands (grey, tan, brown)
Luster: Waxy to vitreous when wet or polished

Identified June 29, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Multi-colored bands (grey, tan, brown); Luster: Waxy to vitreous when wet or polished; Structure: Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.65

Formation & geological history

Formed primarily as a chemical precipitate from silica-rich fluids or the accumulation of siliceous microfossils like diatoms or radiolarians in marine environments. Banding represents seasonal or environmental changes during deposition.

Uses & applications

Historically used for making sharp tools and arrowheads; today used for decorative purposes, landscape gravel, and as a popular choice for rock tumbling and jewelry lapidary.

Geological facts

Chert is so durable that it often survives long after the surrounding rock has weathered away. It was one of the most important minerals for early humans due to its ability to create a spark and hold a razor-sharp edge.

Field identification & locations

Identified by its extreme hardness (cannot be scratched by a steel knife), smooth waxy feel, and distinctive swirled or straight color bands. Commonly found in riverbeds, lakeshores, and coastal areas as rounded pebbles.