mineral

Chalcedony

Silicon dioxide (SiO2) - Microcrystalline quartz

Hardness: 6.5-7 (Mohs scale); Color: Grayish-blue, white, or pale lavender; Luster: Waxy to vitreous; Crystal structure: Trigonal/Monoclinic (cryptocrystalline); Cleavage: None; Specific gravity: 2.58–2.64

Hardness: 6
Color: Grayish-blue, white, or pale lavender
Luster: Waxy to vitreous

Identified January 1, 2026More mineral →

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Physical properties

Formation & geological history

Formed from the precipitation of silica-rich hydrothermal fluids in volcanic cavities (geodes/vugs) or sedimentary environments. It can form at low temperatures in a variety of geological ages, often as a secondary mineral in basaltic rocks or limestones.

Uses & applications

Commonly used as gemstones for jewelry (cabochons), ornamental housewares, carvings, and historically for stone tools due to its conchoidal fracture. It is also a popular collector's item.

Geological facts

The name 'chalcedony' is derived from the ancient Greek town of Chalkedon in Asia Minor. It is actually a mixture of two silica minerals: quartz and moganite. Translucent varieties are often called 'Blue Lace Agate' if they show banding.

Field identification & locations

Identify in the field by its waxy luster, translucency, and lack of visible crystals. It typically has a smooth, rounded (botryoidal) appearance when found in the wild. Common locations include Brazil, Namibia, India, and the United States (Oregon/Arizona).

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