Chrysocolla after Barite with Malachite

specimen number:
8282353

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

description:

Prismatic crystals of what were once likely barite measuring to 3.0 cm in height or coming off this matrix and replaced completely by blue chrysocolla. A later generation of velvety green crystallized malachite scattered throughout. Attractive and interesting.

The Mashamba West Mine, located in the Kolwezi District of the Lualaba Province in the Democratic Republic of the Congo, is a premier locality within the Central African Copperbelt. Geologically, it is a stratiform copper-cobalt deposit hosted in Neoproterozoic sedimentary rocks of the Katanga Supergroup, specifically within the Mines Group. The ore bodies formed through complex diagenetic and hydrothermal processes that mineralized the dolomitic shales and siltstones with primary sulfides, which were later subjected to intense tropical weathering. This weathering created a rich oxidation zone famous for producing world-class specimens of cuprite, malachite, and cobaltian smithsonite. Historically, the mine began as an open-pit operation in the late 1970s, specifically around 1978, under the state-owned company Gecamines. While major industrial production was significant during the 1980s, the mine has experienced periods of inactivity and artisanal working, eventually becoming part of larger corporate concessions like those held by Glencore (KCC). It remains a legendary site for collectors due to the extraordinary size and color of the oxidized copper and cobalt minerals recovered during its peak years.

Pseudomorphs are a fascinating mineralogical phenomenon where one mineral replaces another while retaining the original crystal shape of the first mineral. This process occurs when a primary mineral becomes chemically unstable due to changes in temperature, pressure, or the chemistry of circulating fluids, such as groundwater in an oxidation zone. As the original mineral dissolves or reacts, a new mineral precipitates in its place, essentially acting as a stony cast of the predecessor. In the Mashamba West Mine and surrounding areas, this is frequently seen with malachite replacing azurite or cuprite. The result is a specimen that may have the vibrant green color and silky texture of malachite but possesses the sharp, geometric crystal habit of the original azurite. These "mineral ghosts" are highly prized because they provide a visual record of the chemical evolution and environmental changes that occurred within a geological deposit over millions of years.

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