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Edwardsite from the Tsumeb Mine, Namibia

Analytical investigations of the germanite and renierite associated secondary minerals have lead to the discoveries of many unique minerals eg. otjisumeite, bartelkeite, stottite from the Tsumeb Mine, Otavi Highlands, Namibia in the past decades.

There are still many undescribed Germanium (Ge), Gallium (Ga) bearing secondary minerals present in this assemblage, that lack size or other parameters for further structural work, but the main focus of this article are new Cadmium (Cd) bearing minerals, that are already known from other localities.

These minerals, mainly sulphates, are formed by weathering of Cd rich sphalerite in germanite-chalcocite matrix. These are interesting, as only a small number of other localities and mining areas eg. Lavrion, Greece, and Broken Hill, NSW, Australia in the world are known, where these occur too.

This article is a summary of recently discovered species, that are new for the Tsumeb mine.

The identification was made by the combined use of SEM-EDS, Raman spectroscopy, powder diffraction (PXRD) and microdiffraction.

Edwardsite, Cu3Cd2(SO4)2(OH)6 4H2O, can be found in pale blue crystals up to 50 µm with an arrow-shaped morphology often associated with ktenasite, niedermayrite and sometimes lauraniite. Pictured below, almost centered, is a double terminated greenish-blue edwardsite surrounded by very small triangular lauraniite. The mineral is rather widespread as coatings in this assemblage, but less common in well visible crystals.

Edwardsite from the Tsumeb mine could be confirmed by microdiffraction (A. Kasatkin) and standardless SEM-EDS analysis. We currently have one on germanite matrix in our e-rocks auction. The detailed desciption is available here: 

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Photos: Edwardsite from the Tsumeb Mine, Namibia
Photos: Edwardsite from the Tsumeb Mine, Namibia
Photos: Edwardsite from the Tsumeb Mine, Namibia