Malachite after Azurite

specimen number:
2102428

location:
Morenci Mine, Greenlee Co., Arizona, USA

description:

The top of matrix is covered by large sharp bladed crystals of what were once azurite, these now replaced by deep green crystallized malachite. In great condition. Collected in the early 1990s.

The Morenci mine, located in Greenlee County, Arizona, is one of the largest open-pit copper mining complexes in the world. Geologically, the site is a classic porphyry copper deposit formed during the Laramide Orogeny, where igneous intrusions injected metal-rich hydrothermal fluids into local Paleozoic sedimentary rocks and Precambrian basement formations. Over millions of years, weathering and groundwater movement produced a massive supergene enrichment zone, converting lean primary sulfides into high-grade chalcocite and creating an abundance of secondary copper carbonates. Underground mining in the district began in the early 1870s under various entities, eventually consolidating under the Phelps Dodge Corporation, which transitioned the property to large-scale open-pit mining methods in 1937. Today, the operation utilizes massive southwestern solvent extraction-electrowinning facilities alongside traditional mining, remaining a highly productive industrial site under the ownership of Freeport-McMoRan.

In the early 1990s, specifically around late 1992 and 1993, a remarkable mineralogical discovery occurred within the Northwest Extension of the Morenci open pit, an area alternatively referred to by collectors as part of the incredible pigment zone or blue hole. As heavy machinery pushed benches through this newly exposed section, miners and field collectors encountered highly localized, clay-filled veins packed with massive amounts of copper carbonates. This pocket yielded extraordinary specimens of malachite pseudomorphs after azurite, where original, sharp, deep-blue azurite crystal plates and rosettes had been entirely replaced by velvety, forest-green malachite while perfectly preserving the original crystal forms. The find produced tons of world-class material, creating an immediate sensation among mineralogists and collectors who prized the stark structural definition and rich coloration of these unique pseudomorphs.

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