Malachite after Azurite

specimen number:
2063343

location:
New Cornelia Mine, Ajo, Pima Co., Arizona, USA

description:
A loose cluster of what were once blocky sharp crystals of azurite, the largest crystal 2.0 cm on edge, the entire piece now replaced by deep green lustrous crystallized malachite. This is classic for the locality. In great condition. The specimen comes with a previous label from the collection of Ray DeMark.

Located in the Little Ajo Mountains of Pima County, Arizona, the New Cornelia Mine at Ajo is a massive open-pit porphyry copper deposit formed within Laramide-age granodiorite intrusive rocks. Native Americans and early Spanish prospectors exploited its rich surface copper deposits for pigments and ore long before large-scale commercial mining began in 1917 under the New Cornelia Copper Company, which established it as the first major open-pit copper mine in Arizona. Famed among mineral collectors, the mine's extensive oxidized zone yielded exceptional specimens of minerals such as shattuckite, papagoite, turquoise, malachite, and azurite until major mining operations ceased in the 1980s.

A pseudomorph occurs when one mineral replaces another while preserving the original crystal shape and form of the first mineral. In the specific case of malachite after azurite, the copper carbonate mineral azurite is gradually altered and replaced by malachite, another copper carbonate, due to changing chemical conditions in the oxidation zones of copper deposits. This chemical transformation retains the distinct crystal habit and sharp geometric forms of the original azurite crystals, but completely changes their classic deep blue color into a vibrant emerald green. Famous localities for this classic specimen type include Chessy-les-Mines in France, Tsumeb in Namibia, and various copper districts in the southwestern United States.

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