mineral

Chalcedony (Agate)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Grayish-blue, translucent to opaque; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None; Specific Gravity: 2.58-2.64.

Hardness: 6
Color: Grayish-blue, translucent to opaque
Luster: Waxy to vitreous

Identified June 9, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica-rich fluids in volcanic cavities (vesicles) or sedimentary rock fractures. Often found in basalt flows or as nodules in limestone.

Uses & applications

Used primarily in lapidary arts for jewelry, cabochons, and decorative carvings. Historically used for making tools due to its conchoidal fracture and hardness.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are so small they can only be seen under high magnification. It is a family that includes carnelian, onyx, and agate.

Field identification & locations

Identify in the field by its waxy luster, conchoidal (shell-like) fracture, and translucent edges when held to light. Common in river beds, beaches, and volcanic regions.