mineral

Chalcedony (River or Beach Pebbles)

Chalcedony (Silicon Dioxide, SiO2)

Hardness: 6.5–7 (Mohs scale); Color: translucent tan, honey-yellow, brown, and green; Luster: waxy to vitreous; Crystal Structure: microcrystalline/cryptocrystalline; Cleavage: none; Fracture: conchoidal.

Hardness: 6
Color: translucent tan, honey-yellow, brown, and green
Luster: waxy to vitreous

Identified July 5, 2026More mineral →

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Physical properties

Formation & geological history

These are water-worn cryptocrystalline quartz nodules (chalcedony and chert). They form via the precipitation of silica from groundwater in volcanic or sedimentary cavities. Their rounded shape indicates long-term transport in high-energy aqueous environments like rivers or coastal shorelines.

Uses & applications

Used primarily as decorative gravel, aquarium stones, and for lapidary arts like tumbling or cabochon making. Fine chalcedony is used in jewelry.

Geological facts

The smooth, rounded 'potato' look is caused by constant abrasion against other rocks in water. The green specimens visible in the photo may be green chalcedony (chrysoprase or jasper) or piece of sea glass.

Field identification & locations

Look for a waxy texture and translucency when held to a light source. These are common in riverbeds, glacial till, and coastal beaches globally. They are excellent candidates for rock tumblers.

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