Malachite after Azurite with Quartz

specimen number:
9505727

location:
Tenke-Fungurume, Lualaba, DR Congo

description:

A beautiful specimen showing prismatic crystals of what were once likely azurite to 2.0 cm in length, these replaced by green malachite. The entire specimen is covered with a sprinkling of sparkling micro crystals of quartz. In great condition and quite attractive.

The Tenke-Fungurume mining district, located in the Lualaba Province of the Democratic Republic of the Congo, is one of the worlds largest sediment-hosted copper and cobalt producers. Geologically, the deposits are situated within the Neoproterozoic Katanga Supergroup of the Central African Copperbelt, specifically hosted in the Roan Group rocks that underwent significant folding, faulting, and tectonic thrusting during the Lufilian Orogeny. The rich ore bodies feature deep supergene enrichment zones containing malachite, heterogenite, and chrysocolla overlying primary sulfide mineralization. Historically, indigenous artisanal mining preceded formal European exploration and prospecting in the early 20th century, followed by decades of interrupted development before modern large-scale industrial open-pit operations expanded rapidly in the 21st century.

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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