sedimentary

Tumbled brown chert or jasper

Microcrystalline quartz (SiO₂), likely iron-stained chert/jasper

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque brown to ochre with rusty iron-oxide mottling, waxy to dull luster, and no visible cleavage. It appears water-worn or mechanically tumbled, with a very fine-grained cryptocrystalline structure.

Identified September 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when silica-rich groundwater replaced or cemented sediment, commonly from biochemical silica or volcanic ash; iron oxides produced the brown coloration. Its exact geological age cannot be determined from the photograph and may range from Paleozoic to younger deposits.

Uses & applications

Used as a lapidary stone for cabochons, beads, carvings, and decorative objects; chert is also historically important for toolmaking and occasionally used as aggregate.

Geological facts

Jasper is an opaque, impure variety of microcrystalline quartz, while chert is the broader silica-rock category; the boundary between them is often informal.

Field identification & locations

Identify by testing scratch resistance against steel or glass, checking for a conchoidal fracture, and noting the absence of calcite fizz with dilute acid. Common in river gravels and silica-rich sedimentary formations worldwide.