mineral

Chalcedony (Common Agate)

Silicon Dioxide (SiO₂)

Hardness: 6.5-7 on Mohs scale; Color: Translucent white, cream, and tan with iron staining; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (Trigonal); Cleavage: None; Specific Gravity: 2.58-2.64.

Hardness: 6
Color: Translucent white, cream, and tan with iron staining
Luster: Waxy to vitreous

Identified July 4, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica-rich fluids in cavities or fractures within volcanic or sedimentary rocks. The specimen shows signs of alluvial wear, suggesting it was recovered from a river or stream bed.

Uses & applications

Used in jewelry (cabochons), as an abrasive in some industrial processes, and popular among lapidary hobbyists for tumbling and polishing.

Geological facts

Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. The circular pitting on the surface often results from the weathering of small botryoidal formations or mineral inclusions.

Field identification & locations

Identify in the field by its waxy luster, translucency when held to light, and conchoidal fracture. Common in gravel pits, riverbeds, and volcanic regions worldwide.