mineral

Chalcedony

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale), Color: Smoky grey to translucent white, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline (Trigonal/Monoclinic), Specific Gravity: 2.6-2.64.

Hardness: 6

Identified July 18, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: Smoky grey to translucent white, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline (Trigonal/Monoclinic), Specific Gravity: 2.6-2.64.

Formation & geological history

Formed via the deposition of silica from aqueous solutions at relatively low temperatures, often found in volcanic cavities (vesicles), sedimentary environments, and as a replacement in petrified wood.

Uses & applications

Used primarily in jewelry as gemstones (cabochons), ornamental carvings, and historically for stone tools due to its conchoidal fracture. Also used as an abrasive in industrial applications.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are so small they can only be seen under extreme magnification. It has been used by humans for thousands of years, notably by the Minoans on Crete for seal stones.

Field identification & locations

Identify in the field by its waxy luster, translucency, and shell-like (conchoidal) fracture when broken. It is a common find in gravel beds and dry washes in volcanic regions throughout the Western United States and Brazil.