sedimentary

Beach Agate / Chalcedony Pebble

Silicon Dioxide (SiO2) - Microcrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs. Color: translucent grey, beige, and brown with fine white banding and quartz veining. Luster: vitreous to waxy when wet/polished. Structure: microcrystalline/cryptocrystalline. Specific gravity: ~2.6.

Hardness: 6
Luster: vitreous to waxy when wet/polished

Identified July 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by secondary deposition of silica-rich fluids filling cavities (vesicles) within volcanic rocks or fractures in sedimentary beds. Subsequently eroded and naturally rounded by coastal wave action over thousands of years.

Uses & applications

Popular for rock tumbling, lapidary arts, jewelry components, cabochon cutting, and amateur rockhounding collections.

Geological facts

Agates are microcrystalline varieties of quartz known for their translucency and concentric or horizontal banding patterns. Ocean waves naturally polish these stones, giving them a smooth, rounded pebble shape.

Field identification & locations

Look for translucency when backlit by a flashlight, along with fine linear banding or quartz cross-veins on smooth coastal pebbles. Commonly found along gravel beaches and riverbanks in active geological zones.