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, opaque to slightly translucent, with a waxy-to-glassy luster and no visible cleavage. The smooth rounded form appears water-worn or mechanically tumbled; fine granular texture and possible iron-oxide staining are present.

Identified August 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich fluids replace or cement sediment, commonly in marine limestone or volcanic-sedimentary settings; chalcedony forms from low-temperature silica deposition. Formation ages vary widely, from Precambrian to recent, and cannot be determined from the image.

Uses & applications

Used as a durable aggregate, tool material, decorative stone, and lapidary material; attractive translucent pieces may be cut or polished for cabochons and beads.

Geological facts

Chert and chalcedony are quartz varieties distinguished mainly by texture and translucency; chert was widely used by prehistoric peoples for sharp-edged tools.

Field identification & locations

Identify by its waxy appearance, very high hardness, lack of cleavage, and inability to scratch it with a steel knife; quartz should scratch glass. Common in gravel beds, limestone regions, river deposits, and glacial till.