sedimentary

Banded Chert

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7.0 (Mohs scale); Color: Dark grey, greenish, and brown with distinct banding; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture)

Hardness: 6
Color: Dark grey, greenish, and brown with distinct banding
Luster: Waxy to vitreous

Identified May 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the accumulation of siliceous remains from microscopic organisms like diatoms or radiolarians, or through chemical precipitation in marine environments. Bands represent varying mineral impurities or depositional rates.

Uses & applications

Used historically for stone tools and weapons due to its sharp fracture edges. Today it is used in lapidary work, jewelry (cabochons), and as landscaping/decorative stones.

Geological facts

Chert is one of the oldest materials used by early humans for flintknapping. In its polished form, it is often sold as 'river stone' or 'pocket stones' for meditation.

Field identification & locations

Identify by its hardness (cannot be scratched by steel) and smooth, waxy surface when polished. Look for it in sedimentary basins or as rounded pebbles in riverbeds and beaches.