mineral

Chalcedony (Common Opal variant)

Silicon dioxide (SiO2) with microcrystalline structure

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Milky white to pale yellow/honey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.58-2.64

Hardness: 6
Color: Milky white to pale yellow/honey
Luster: Waxy to vitreous

Identified May 15, 2026More mineral →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Milky white to pale yellow/honey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.58-2.64

Formation & geological history

Formed from the deposition of silica-rich water in cavities of volcanic and sedimentary rocks at low temperatures. Common in various geological ages ranging from Cenozoic to ancient Precambrian deposits.

Uses & applications

Used in gemstone carvings, jewelry making, lapidary arts, and as a collector's specimen. Historically used for making tools and seals.

Geological facts

Chalcedony was highly prized in antiquity; the name is derived from the ancient Greek town of Chalkedon. It is a fibrous cryptocrystalline form of silica.

Field identification & locations

Identify in the field by its waxy luster, conchoidal fracture (curved glass-like breaks), and lack of visible crystals. Commonly found in desert environments, riverbeds, and volcanic geodes.