sedimentary

Tumbled quartz-rich chert or chalcedony pebble

Microcrystalline silica (SiO₂), likely chert/chalcedony

AI-generated identification · may be incorrect

Smooth, water-worn oval with tan-brown coloration, waxy to dull luster, and faint translucent edges; hardness about 6.5–7 Mohs, no visible cleavage, cryptocrystalline structure, and specific gravity near 2.6. Iron-oxide staining likely produces the brown tones.

Identified August 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Most likely formed when silica-rich groundwater replaced or cemented sediment, producing microcrystalline quartz; later erosion rounded it in a stream, beach, or gravel deposit. The formation age cannot be determined from the image and may range from Paleozoic to recent reworking.

Uses & applications

Commonly used as aggregate, road material, landscaping stone, and occasionally for flaked tools or decorative lapidary work. This specimen has modest collector value unless its locality or pattern is distinctive.

Geological facts

Chert and chalcedony can look similar; chalcedony is generally more translucent and evenly waxy, while chert is often more opaque and irregularly colored.

Field identification & locations

Test cautiously: it should resist scratching by a steel knife and may scratch glass; a fresh break is typically smooth, curved, and sharp-edged. Common in sedimentary terrains, river gravels, and glacial deposits.