sedimentary
Banded Chert / Flint Pebble
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, off-white, cream, and charcoal gray in irregular bands; Luster: Waxy to dull; Fracture: Conchoidal; Specific Gravity: ~2.65.
- Hardness
- 7 on Mohs scale
- Color
- Gray, off-white, cream, and charcoal gray in irregular bands
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, off-white, cream, and charcoal gray in irregular bands; Luster: Waxy to dull; Fracture: Conchoidal; Specific Gravity: ~2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation of microcrystalline silica in marine environments, followed by compaction and diagenesis. Frequently smoothed by wave or stream erosion into a rounded pebble.
Uses & applications
Historically used for making stone tools, arrowheads, and strike-a-lights due to its sharp conchoidal fracture. Modern uses include decorative landscaping, gravel, tumbling, and lapidary practice.
Geological facts
Banded chert often displays striking contrasting layers caused by minor mineral impurities, such as organic carbon (grays/blacks) or iron oxides (reds/browns), preserved during sedimentation.
Field identification & locations
Easily identified by its smooth, waxy surface, inability to be scratched by a steel knife, and classic conchoidal fracture lines. Commonly found along riverbeds, glacial deposits, and ocean beaches worldwide.
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