Malachite after Azurite with Azurite

specimen number:
1052487

location:
Tsumeb Mine, Otjikoto, Namibia

description:
Classic specimen from Namibia with thick prismatic double terminated crystal of what was once azurite 3.0 cm in length, this now replaced by green malachite, and laying across a bed bright blue crystallized azurite. In good condition. This is from the early days of mining at this famous locality, the specimen comes with a pair of antique labels that dates this to the very early 20th century.

The Tsumeb Mine in Namibia is one of the most famous polymetallic deposits in the world, with large scale mining beginning around 1905 and continuing until final closure in 1996. The deposit is a complex pipe like ore body hosted in dolomitic limestone and is exceptionally rich in copper, lead, zinc, and many rare elements. Extensive underground workings reached great depths and produced a remarkable variety of minerals, especially from the oxidized zones where secondary mineralization developed. Tsumeb became renowned not only for its economic output but also for its extraordinary mineral diversity, making it one of the most studied and collected localities in mineralogy.

Pseudomorphs are minerals that have replaced an earlier mineral while preserving the original external crystal form. At Tsumeb, one of the most well known examples is malachite after azurite, where original blue azurite crystals were chemically altered and replaced by green malachite over time. This process occurs in the oxidized zone as changing conditions cause azurite to become unstable and dissolve while malachite precipitates in its place. The resulting specimens retain the sharp crystal shape of azurite but are composed entirely of malachite, often creating striking color contrasts and providing clear evidence of mineral replacement processes.

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