Kolwezite after Cuprite with Calcite

specimen number:
8282052

location:
Kakanda, Lubudi, Lualaba, DR Congo

description:

A colorful and interesting specimen showing crystals of what were once cuprite measuring to 1.0 cm in size scattered across the front of a matrix covered by botryoidal brilliant pink crystallized calcite. The cuprite crystals have been replaced by olive green kolwezite. This is in really good condition.

The Kakanda mining district, located in the Lualaba Province of the Democratic Republic of the Congo, is a notable copper and cobalt producing area centered around its historical open-pit operations. Geologically, the deposit sits within the Central African Copperbelt and is hosted in the Neoproterozoic sedimentary sequences of the Katanga Supergroup, where a series of highly faulted and brecciated fragments from the Mines Subgroup contain stratiform copper-cobalt mineralization that underwent extensive supergene enrichment. Large-scale industrial mining began under Belgian colonial administration with the Union Miniere du Haut-Katanga in the mid-twentieth century and was later nationalized under the state-owned company Gecamines in 1967. While formal high-volume industrial mining by Gecamines and joint-venture partners fluctuated and largely wound down by the late twentieth century, the locality has seen continuous, intensive artisanal quarrying and surface mining stretching well into the 2020s.

Kolwezite is a rare copper cobalt carbonate hydroxide mineral where copper and cobalt replace one another within a structural framework closely related to malachite. Typically forming as beige-brown, blackish-brown, or distinct pale green microcrystalline crusts, nodular masses, and tiny radiating spherical aggregates, it is classified as a member of the rosasite mineral group. First discovered and approved as a valid mineral species in 1980 from its type locality near Kolwezi, this secondary mineral crystallizes exclusively within the highly oxidized zones of cobalt-rich hydrothermal copper deposits where carbonate-bearing fluids react with primary sulfides.

A pseudomorph occurs when a mineral completely replaces a preexisting crystal atom-for-atom, maintaining the original outward shape and structural geometry while entirely changing the chemical composition. In the case of kolwezite after cuprite, changes in the chemical environment and fluid composition within the weathering zone cause the copper oxide, cuprite, to gradually alter into the copper cobalt carbonate, kolwezite. This process yields highly distinctive and collectable specimens where dark green or brownish kolwezite perfectly preserves the sharp, geometric octahedral or cubic crystal forms of the original cuprite, frequently set against a contrasting matrix of pink cobaltian calcite.

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