mineral

Chalcedony (Agate Pebble)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Translucent pale yellow to grayish; Luster: Waxy to vitreous; Structure: Cryptocrystalline (hexagonal crystal system at microscopic level); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64

Hardness: 6
Color: Translucent pale yellow to grayish
Luster: Waxy to vitreous

Identified July 10, 2026More mineral →

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Physical properties

Formation & geological history

Formed from the deposition of silica-rich groundwater in cavities of volcanic or sedimentary rocks. This specific specimen appears to be a water-worn river pebble, having been smoothed by fluvial transport.

Uses & applications

Used primarily in lapidary work for making beads, cabochons, and decorative carvings. Industrial uses include mortars and pestles for chemical labs due to its hardness.

Geological facts

Chalcedony has been used since the Bronze Age for seal stones and jewelry because it does not stick to wax. It is the broad term for all microcrystalline quartz varieties including agate, carnelian, and onyx.

Field identification & locations

Commonly found in river beds or areas with volcanic history. Can be identified by its waxy luster, translucency when held to light, and its inability to be scratched by a steel knife.