Malachite after Azurite with Calcite

specimen number:
8282070

location:
Mashamba West Mine, Kolwezi, Lualaba, DR Congo

description:

A sharp crystal of what was once azurite 3.0 cm across and replaced by green crystallized malachite is set up on a crystallized calcite matrix. This is in terrific condition.

The Mashamba West mine, located near Kolwezi in the Lualaba Province of the Democratic Republic of the Congo, is a famous open-pit copper and cobalt operation renowned for producing world-class specimens of cuprite and malachite. Geologically, the deposit belongs to the Central African Copperbelt and is hosted within the Neoproterozoic sedimentary rocks of the Katanga Supergroup, specifically the Mines Subgroup, where primary copper-cobalt stratification underwent intense folding, faulting, and deep supergene enrichment. Supergene weathering in the upper oxidized zones allowed meteoric waters to dissolve primary sulfides and reprecipitate an array of vibrant secondary carbonate minerals in massive vugs and fractures. Commercial open-pit mining began in 1978 under the state-owned mining company Gecamines, which extracted high-grade ore continuously until operations ceased and the pit flooded in the late 1980s due to political and economic shifts. Since the formal closure, the site has seen intermittent activity by artisanal miners who continue to access the upper benches and surrounding exposures to recover world-class collector specimens well into the 2020s.

A pseudomorph is a mineral specimen that has replaced another mineral atom-for-atom, completely altering the chemical composition while perfectly preserving the original crystal shape, habits, and outward geometry of the precursor species. In the case of malachite replacing azurite, the transformation occurs when changes in groundwater chemistry, acidity, or carbon dioxide levels cause the chemically unstable azurite to alter into the more stable copper carbonate, malachite. This gradual chemical substitution leaves a specimen that displays the distinct, sharp, bladed or prismatic crystal forms typical of azurite, but is composed entirely of a rich, velvety green malachite. The Mashamba West mine is globally celebrated for producing some of the finest examples of these sharp green pseudomorphs, highly sought after by collectors for their morphological preservation and intense color contrast.

Questions about this specimen?
Send an email or call us: 314-341-1811.