mineral

Chalcedony Pebble

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: brownish-tan to semi-translucent grey-brown; Luster: waxy to dull/earthy when weathered; Crystal Structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: none, conchoidal fracture

Hardness: 6
Color: brownish-tan to semi-translucent grey-brown
Luster: waxy to dull/earthy when weathered

Identified July 27, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica-rich fluids in cavities, fractures, and sedimentary rocks at low temperatures. Subsequently smoothed and rounded by river, stream, or ocean water erosion.

Uses & applications

Commonly collected as river pebbles, used in rock tumbling, lapidary arts, decorative landscaping, and occasionally carved into small beads or cabochons.

Geological facts

Chalcedony is a cryptocrystalline form of silica composed of microscopic intergrowths of quartz and moganite. Water-worn pebbles often develop a soft, frosted waxy rind from long-term stream transport.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy to resinous texture, and partial translucency when held up to a light source. Extremely common along riverbeds, beaches, and gravel bars worldwide.