sedimentary

Banded Chert (Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7.0 (Mohs scale); Color: Brown, yellow, and grey banding; Luster: Waxy to vitreous; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.65

Hardness: 6
Color: Brown, yellow, and grey banding
Luster: Waxy to vitreous

Identified July 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by chemical precipitation from hydrothermal fluids in sedimentary environments. Common in Precambrian and Paleozoic formations.

Uses & applications

Primarily used for lapidary work, jewelry (tumbled stones), and historically for tool-making (arrowheads) due to its sharp edges when fractured. Valued by collectors as a decorative stone.

Geological facts

Chert is so durable that it often survives long after the surrounding rock has weathered away. The brown and yellow hues are typically caused by iron oxide (limonite or goethite) impurities.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, waxy surface when polished. Commonly found in riverbeds, glacial tills, and sedimentary outcrops.