mineral

Chalcedony (Agate/Carnelian type)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Translucent yellowish-brown to tan; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.64.

Hardness: 6
Color: Translucent yellowish-brown to tan
Luster: Waxy to vitreous

Identified April 13, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in cavities of volcanic rocks or sedimentary formations. This specimen appears water-worn, likely from a river or beach environment.

Uses & applications

Commonly used for lapidary work, jewelry making (cabochons), and as decorative pocket stones. Also historically used for making hard-wearing tools or seals.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are so small they can only be seen under high magnification. Small river-tumbled pieces like this are often called 'river agates'.

Field identification & locations

Identify by its waxy luster, translucency when held to light, and ability to scratch glass. Commonly found in gravel beds, shorelines, and volcanic regions.

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