mineral

Agate pebble (with blue chalcedony exposure)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on the Mohs scale. Color: Tan-brown exterior with pitted texture revealing a deep blue chalcedony core. Luster: Dull or waxy exterior, vitreous inside. Crystal Structure: Microcrystalline/Cryptocrystalline trigonal quartz. Cleavage: None, exhibits conchoidal fracture.

Hardness: 6
Luster: Dull or waxy exterior, vitreous inside

Identified July 22, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater within cavities or vesicles in volcanic rocks (such as basalt) or sedimentary host rocks. Water erosion rounded the outer surface over time.

Uses & applications

Mainly collected by rockhounds, used for tumbling, lapidary arts, jewelry, and ornamental display.

Geological facts

The pitted surface is characteristic of weathered agate pebbles that have suffered river or beach erosion, where softer outer matrix materials wear away to expose internal agate/chalcedony pockets.

Field identification & locations

Can be identified in the field by its high hardness, smooth river-worn shape, and typical pitted exterior revealing microcrystalline quartz or chalcedony inside. Common along gravel bars, river beds, and glacial deposits.

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