sedimentary

Tumbled 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 mustard-brown, earthy to dull luster, very fine-grained cryptocrystalline structure, with no visible cleavage and conchoidal fracture when broken. The rounded shape indicates natural stream abrasion or tumbling.

Identified September 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or cements sediment, commonly during diagenesis in marine limestone or volcanic-sedimentary settings; its exact geological age cannot be determined from the image. Brown coloration is caused mainly by iron oxides and hydroxides.

Uses & applications

Used as aggregate, road material, landscaping stone, lapidary material, and occasionally carved or polished as decorative jasper. This specimen has little gem value unless it displays unusual patterns or translucency.

Geological facts

Chert and jasper are varieties of microcrystalline quartz; jasper is typically opaque and impurity-rich, while chert may be gray, brown, red, or black.

Field identification & locations

Common in gravel beds, river channels, glacial deposits, and sedimentary terrains worldwide. Test identification with a steel file or glass-scratch test—quartz-rich material scratches glass; inspect a fresh fracture for a waxy surface and conchoidal break.