mineral

Blue Chalcedony

Chalcedony (cryptocrystalline Silicon Dioxide, SiO2)

Hardness: 6.5–7 on Mohs scale; Color: Pale blue, lavender-blue, or grayish-blue; Luster: Vitreous to waxy; Structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None; Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Pale blue, lavender-blue, or grayish-blue
Luster: Vitreous to waxy

Identified February 8, 2026More mineral →

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Physical properties

Formation & geological history

Formed by the deposition of silica from aqueous solutions in volcanic and sedimentary environments. It often fills cavities (gas bubbles) in igneous rocks or fractures in sedimentary formations. It can date from almost any geological era containing silica-rich hydrothermal activity.

Uses & applications

Used primarily in jewelry (beads, cabochons, carvings), as ornamental stones, and semi-precious gemstones. Historically used for seals and amulets.

Geological facts

Chalcedony is a cryptocrystalline form of quartz and moganite intergrown. Blue chalcedony is particularly prized for its 'Tyndall scattering,' which causes it to have a hazy, ethereal blue glow when light passes through it.

Field identification & locations

Identify in the field by its waxy luster, conchoidal fracture, and lack of visible crystal faces. Common locations include Namibia (African Blue), Turkey, India, Brazil, and the USA (Oregon and California). Used by collectors to identify silica-rich hydrothermal deposit zones.

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