sedimentary

Polished brown chert or jasper pebble

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

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque brown with a smooth tumbled surface, waxy to dull luster, and a pale cream vein or fracture filling. Microcrystalline quartz lacks visible crystal faces and has no obvious cleavage; specific gravity is about 2.6.

Identified August 21, 2026More sedimentary →

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Physical properties

Formation & geological history

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

Uses & applications

Used as an ornamental stone, cabochon, lapidary material, and occasionally aggregate; this small tumbled piece has modest decorative value.

Geological facts

The cream line may be quartz or calcite filling a fracture, or a contrasting chert band. Chert commonly produces a sharp conchoidal fracture when freshly broken.

Field identification & locations

Identify by its very high hardness, fine-grained appearance, opaque brown body, and inability to scratch with a steel knife easily; it should scratch ordinary glass. Common in sedimentary formations and stream gravels worldwide.