sedimentary

Tumbled banded chert or jasper

Microcrystalline quartz (chalcedony), SiO₂, with iron-oxide impurities

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; brown, gray, and dark bands; waxy to glassy luster; opaque; cryptocrystalline quartz with no visible cleavage. The smoothly polished surface indicates a tumbled or water-worn specimen.

Identified September 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed when silica-rich fluids replaced or cemented fine sediment, with iron oxides producing the brown coloration and banding. Such cherts and jaspers range from Precambrian to much younger ages and occur in sedimentary environments worldwide.

Uses & applications

Used for cabochons, beads, ornaments, lapidary carvings, and decorative stone; chert is also historically important for cutting tools and fire-starting.

Geological facts

Chert and jasper are varieties of microcrystalline quartz; jasper is generally more opaque and impurity-rich. Banding may reflect repeated changes in sediment composition or silica and iron deposition.

Field identification & locations

Identify by its very hard, opaque, fine-grained body, conchoidal fracture, and inability to scratch with a steel knife while scratching ordinary glass. Common sources include sedimentary formations in the United States, Australia, South Africa, and India.