Malachite after Azurite

specimen number:
1052534

location:
Tsumeb Mine, Otjikoto, Namibia

description:
A grouping of prismatic azurite crystals 2.5 cm in height coming off matrix and replaced by chatoyant green crystallized malachite. In good condition. The specimen comes with an antique label as shown at the end of the video and dates to the very early days of mining at this famous locality.

The Tsumeb Mine, located in the Oshikoto Region of northern Namibia, is widely considered the most significant mineral locality in the world. Geologically, the deposit is a massive hydrothermal pipe-like structure that penetrates through a thick sequence of Neoproterozoic carbonate rocks belonging to the Otavi Group. This pipe, which extends over 1400 meters deep, was formed by the collapse of a prehistoric cave system that was subsequently filled with polymetallic mineralizing fluids rich in copper, lead, zinc, and silver. Historically, the outcrop was known to local tribes for centuries, but industrial mining began in 1907 under the South West Africa Company. The mine operated for nearly nine decades before closing in 1996, producing an incredible array of over 300 different mineral species, many of which are found nowhere else on Earth.

A pseudomorph is a mineralogical phenomenon where one mineral replaces another in such a way that the internal chemistry changes while the original external crystal shape is perfectly preserved. This "false form" occurs when a pre-existing crystal becomes unstable due to changes in temperature, pressure, or chemical environment, allowing a new mineral to slowly take its place. In the case of malachite after azurite, the process involves a chemical transition where the deep blue azurite loses carbon dioxide and gains water to transform into the stable green malachite. The result is a specimen that looks exactly like a sharp, bladed or tabular azurite crystal but is composed entirely of vibrant, velvety green malachite.

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