Mimetite

Tsumeb Mine (Ongopolo Mine), Tsumeb, Oshikoto Region, Namibia

Slender, prismatic Mimetite crystals in a clear, bright yellow are scattered across the whole face of this specimen. They lie at every angle, cross one another and reach deep into the cavities of the porous gray matrix, and their flat, mirror-like terminations catch the light from many directions. Bright orange, limonitic coatings frame the edges and set off the yellow. The specimen is unusually heavy for its size, which suggests a core of massive Tennantite beneath the limonite, though this has not been confirmed. That would fit the geology of Tsumeb, where weathering arsenic-bearing ores such as Tennantite supplied the arsenic for Mimetite and the mine’s other arsenates. Tsumeb is widely regarded as the world’s finest locality for Mimetite, and a piece this richly covered shows why. Photo: Matthew Parshchikov