mineral

Chalcedony

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Bluish-white, gray, or tan; Luster: Waxy to vitreous; Crystal Structure: Trigonal (monoclinic morphs common); Fracture: Conchoidal; Specific Gravity: 2.6

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

Identified July 18, 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: Trigonal (monoclinic morphs common); Fracture: Conchoidal; Specific Gravity: 2.6

Formation & geological history

Formed by the deposition of silica from aqueous solutions at relatively low temperatures, often in volcanic rock cavities or sedimentary environments as nodules or veins.

Uses & applications

Used primarily in jewelry as cabochons or beads, for ornamental carvings, and historically for stone tools and seals.

Geological facts

The name comes from the Latin 'chalcedonius', derived from the name of the ancient Greek town Chalcedon in Asia Minor. It is a broad term that includes agate, carnelian, and onyx.

Field identification & locations

Identify in the field by its waxy luster, conchoidal fracture (curved glass-like breaks), and high hardness. Commonly found in riverbeds or volcanic regions like the American Southwest.