Adamite

Adamite is a zinc arsenate hydroxide, Zn₂(AsO₄)(OH), belonging to the olivenite group and crystallizing in the orthorhombic system as wedge-shaped prisms, druses, and radiating sprays with a vitreous to adamantine luster. It forms as a secondary mineral in the oxidized zones of zinc- and arsenic-bearing hydrothermal deposits, typically alongside hemimorphite, austinite, smithsonite, olivenite, legrandite, and limonitic iron oxides. Colors range from honey-yellow and lime-green to blue, pink, and violet depending on trace substitutions: copper produces the vivid green cuprian adamite, cobalt yields pink to violet cobaltoan adamite, and manganese gives rise to manganoan adamite. At Mohs hardness 3.5 with a specific gravity of 4.32–4.48, adamite is soft and brittle, prized purely as a display and fluorescent-mineral species rather than for any industrial use.

The type locality is the historic Chañarcillo silver-zinc district in the Atacama Region of Chile, where the species was first described in 1866 from yellow crystals of the Dolores mine. Its defining occurrence, however, is the Ojuela Mine at Mapimí, Durango, Mexico, a limestone-replacement deposit whose oxidized zone has produced the world's finest and most fluorescent adamite: lime-green to yellow crystal sprays on contrasting red-brown limonite gossan, often rivaling Franklin willemite in shortwave UV brilliance thanks to uranyl-ion activation. Other classic sources include the ancient Lavrion (Laurium) mining district in Greece, celebrated for green to blue-green crystals; Tsumeb in Namibia, source of rare cobaltoan blue and violet material from one of the world's most mineralogically diverse ore bodies; Cap Garonne in France; the Dachang ore field at Nandan, Guangxi, China; and, in the United States, Gold Hill in Tooele County, Utah, and Chloride Cliff in Death Valley, California.

Collectors seek adamite for the striking contrast between its jewel-toned, often gemmy crystals and dark gossan matrix, and for its dramatic response under both longwave and shortwave ultraviolet light, glowing bright green, yellow-green, or bluish-white. Because fluorescence intensity varies enormously even between specimens from the same pocket, connoisseurs specifically hunt for the brightest Mapimí pieces and rare color varieties such as cuprian or cobaltoan adamite. Its combination of vivid natural color, fine crystal form, and UV performance makes adamite a cornerstone species for both aesthetic mineral collections and dedicated fluorescent-mineral cabinets.