mineral

Chalcedony / Quartz Pebble

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Grayish-white, translucent to semi-opaque; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: ~2.65.

Hardness: 7 on Mohs scale
Color: Grayish-white, translucent to semi-opaque
Luster: Waxy to vitreous

Identified July 26, 2026More mineral →

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Physical properties

Formation & geological history

Formed in volcanic cavity gas bubbles (geodes) or sedimentary environments through precipitation of silica-rich fluids. Often rounded by water erosion in stream beds or beach gravel deposits.

Uses & applications

Commonly used for lapidary work, tumbling, decorative landscaping, and collecting as a raw silica specimen.

Geological facts

Microcrystalline quartz varieties like chalcedony are composed of microscopic intergrowths of quartz and moganite. Water-worn pebbles often feature botryoidal textures or banding under the weathered exterior.

Field identification & locations

Identify by its waxy luster, hardness (can scratch glass and steel), smooth water-worn surface, and light translucency when backlit. Commonly found in riverbeds, gravel pits, and ancient alluvial deposits.