Eyselite

In 1977, Professor Terry Seward acquired several germanium-rich ore samples from Windhoek mineral dealer Sid Pieters. A secondary mineral hosted by a vug on one of these samples was analysed by XRD in the early 1990s but could not be identified. In 2002, the material was submitted to Andy Roberts at the Geological Survey of Canada who determined that it was a new species (Roberts et al. 2004). Eyselite (IMA 2003-052) was named for Walter H. Eysel, professor of crystallography at the Ruprecht-Karls University, Heidelberg, Germany, recognising his contributions to the mineralogy of germanates and to the Powder Diffraction File. Type material is conserved at Eidgenössische Technische Hochschule, Zürich, Switzerland (no specimen number) and at the Geological Survey of Canada, Ottawa (catalogue number 68093).

Eyselite is an exceptionally rare mineral. On the type specimen it occurs in a vug (4 x 5 mm) in germanite ore (renierite and germanite) with minor tennantite, almost certainly from the second oxidation at Tsumeb. Eyselite formed from the alteration of germanium ore by oxidising ground water; however, no other secondary minerals are associated. Individual crystals of eyselite (typically subhedral, platy to prismatic and not exceeding 20 µm in length) are tan-yellow in colour and transparent with a vitreous lustre. They form opaque and dirty brown-yellow aggregates coating sulphide surfaces.

germanite; renierite; tennantite-(Zn)