sedimentary

Banded chert or silicified sedimentary rock

Microcrystalline quartz (chalcedony), SiO₂, with iron-oxide and other mineral bands

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray, cream, and rusty-yellow layered color; waxy to dull luster; very fine-grained, with no visible cleavage and irregular to conchoidal fracture. The specimen appears naturally weathered or possibly cut and lightly polished.

Identified August 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed when silica-rich fluids replaced or cemented layered sediment, commonly in ancient marine basins; iron oxidation produced the yellow-brown bands. Its precise geological age cannot be determined from the photograph.

Uses & applications

Used as lapidary material, cabochons, carvings, and decorative stone; dense chert is also useful for toolmaking and aggregate. This small ordinary specimen has limited commercial value.

Geological facts

The parallel banding and very fine texture distinguish chert from many coarse-grained rocks, though visual identification alone is not definitive. A steel file should barely scratch it, while quartz should not.

Field identification & locations

Common in sedimentary formations worldwide, including the Ozarks, Great Lakes region, western U.S., Europe, and Australia. Confirm with a streak test, hardness test, close examination of fracture, and ideally a silica/iron-mineral analysis.