sedimentary

Tumbled chert or chalcedony pebble

Microcrystalline quartz (SiO₂), likely chert/chalcedony

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; tan to honey-brown, dull to waxy luster, very fine-grained and massive with conchoidal-looking fractures. No visible crystal faces or cleavage; density typically 2.6 g/cm³.

Identified September 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich fluids replace or cement sediment, commonly from biogenic silica, during sedimentary diagenesis; its age depends on the host formation and may range from Paleozoic to recent. The rounded shape indicates stream or beach transport and/or tumbling.

Uses & applications

Used for decorative stones, lapidary carvings, beads, and historically for sharp tools and fire-starting. This ordinary specimen has little commercial value.

Geological facts

The image cannot distinguish chert from jasper, chalcedony, or a polished concretion with certainty. A glassy fracture and ability to scratch ordinary glass support quartz-rich material.

Field identification & locations

Common in gravel beds, beaches, river channels, and sedimentary outcrops worldwide; look for waxy texture, lack of cleavage, and conchoidal fracture. Estimated value: $1–$10 for a common pebble, or $10–$40 if unusually attractive and polished.