mineral

Chalcedony

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Pale blue, grey, white, or yellowish; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None; Specific Gravity: 2.58-2.64

Hardness: 6
Color: Pale blue, grey, white, or yellowish
Luster: Waxy to vitreous

Identified March 2, 2026More mineral →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Pale blue, grey, white, or yellowish; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None; Specific Gravity: 2.58-2.64

Formation & geological history

Formed through the precipitation of silica from groundwater in cavities of various rock types, including volcanic lavas and sedimentary layers. It can form at relatively low temperatures.

Uses & applications

Used primarily in jewelry (cabochons, beads), ornamental carvings, and historical seals. Also used in precision instruments for its hardness and resistance to chemicals.

Geological facts

Chalcedony was highly prized in the ancient world; many ancient Greek and Roman signet rings were carved from it. It is actually a microcrystalline variety of quartz.

Field identification & locations

Identify in the field by its waxy luster, conchoidal fracture, and translucency. It often appears as nodules or botryoidal (grape-like) masses. Common in Brazil, India, and the southwestern USA.