Aurichalcite

Aurichalcite is a secondary mineral consisting of copper and zinc carbonate hydroxide. It forms in oxidized zones of copper-zinc ore deposits and is valued for its distinctive blue to blue-green coloration.

Chemically, aurichalcite comprises copper and zinc in a carbonate-hydroxide lattice. The idealized formula is often represented as (Cu,Zn)5(CO3)2(OH)6, reflecting variable copper-to-zinc composition. It is described as a hydrous basic copper zinc carbonate mineral, with composition that can shift within a solid solution range depending on local ore chemistry.

In hand specimens, aurichalcite typically appears as delicate, often tabular or prismatic crystals, or as opaque to translucent crusts and coatings. The color ranges from sky blue to greenish blue, and the mineral commonly exhibits a vitreous to pearly luster. Mohs hardness is about 3.5 to 4, and its specific gravity is approximately 3.7 to 3.9, making it relatively light for a copper-containing mineral.

Aurichalcite occurs worldwide in association with other secondary copper minerals such as malachite, azurite, chrysocolla, and hemimorphite, as well as zinc-bearing phases like smithsonite. It is especially noted from oxidized portions of copper-zine ore systems and their transition zones, where weathering processes concentrate copper and zinc into carbonate-hydroxide phases.

The name aurichalcite derives from aurichalcum, the ancient term for a copper–zinc alloy, reflecting the mineral’s copper–zinc composition and its characteristic blue-green hue.