mineral

Chalcedony Pebble

Silicon Dioxide (SiO2)

Mohs hardness of 6.5-7. Translucent to semi-translucent body with waxy to vitreous luster. Color ranges from brownish-pink, grey, to reddish-brown with internal fractures or banding. Trigonal crystal system (microcrystalline/cryptocrystalline aggregate). Conchoidal fracture, no cleavage. Specific gravity approx 2.6.

Identified July 27, 2026More mineral →

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Physical properties

Formation & geological history

Forms at relatively low temperatures through the precipitation of silica-rich fluid in cavities, veins, or sedimentary rock voids, often worn smooth into river or beach pebbles by hydraulic erosion.

Uses & applications

Popular for lapidary work, tumbling, wire wrapping, gemstone cabochons, decorative carving, and rock collecting.

Geological facts

Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. Water-worn pebbles often develop a soft, frosted exterior texture from natural tumbling.

Field identification & locations

Identified in the field by its hardness (scratches glass), waxy luster, smooth rounded shape, and waxy shell-like (conchoidal) fractures. Widely found along gravel bars, riverbeds, and ocean beaches globally.