mineral

Chalcedony

Chalcedony (SiO2)

Hardness: 6.5-7 Mohs; Color: Bluish-white, gray, or tan; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.6-2.64

Hardness: 6
Color: Bluish-white, gray, or tan
Luster: Waxy to vitreous

Identified May 23, 2026More mineral →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Bluish-white, gray, or tan; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.6-2.64

Formation & geological history

Formed from the deposition of silica-rich water in cavities of volcanic or sedimentary rocks at relatively low temperatures. Often found in geodes and as nodules.

Uses & applications

Used extensively in jewelry as cabochons, lapidary carvings, ornamental stones, and historically for tools due to its sharp conchoidal fracture.

Geological facts

Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. Agate and Onyx are specific varieties of chalcedony.

Field identification & locations

Identify by its waxy luster, lack of visible crystals, and conchoidal fracture. Often found in arid desert environments or volcanic ash beds. Look for translucency when held to light.