mineral

Blue Chalcedony

Cryptocrystalline Quartz (SiO2)

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

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

Identified July 15, 2026More mineral →

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Physical properties

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

Formation & geological history

Formed from volcanic activity and groundwater deposition. Silica-rich fluids precipitate in cavities of igneous rocks or sedimentary layers, often at low temperatures. Common in Cenozoic deposits.

Uses & applications

Used extensively in jewelry for cabochons and beads, ornamental carvings, and historically for stone tools and seals.

Geological facts

Chalcedony was named after the ancient Greek town of Chalcedon. It has been used for over 3,000 years to carve seals because wax does not stick to it.

Field identification & locations

Identify by its waxy luster and conchoidal fracture. Often found as rounded pebbles in riverbeds or within volcanic nodules (geodes). Common in Brazil, Namibia, Turkey, and the USA.