Bartelkeite

Bartelkeite is an exceptionally rare mineral, one of scarce natural germanium compounds. The formula was originally assumed to be PbFeGe₃O₈, bartelkeite was later shown to be isostructural with a high-pressure form of the mineral lawsonite. Thus, its correct formula is PbFeGe₂•H₂O. Bartelkeite and mathewrogersite are minerals with essential lead, iron and germanium. Both come from Tsumeb, Namibia - a world's "capital" of germanium minerals.

Occurrence and association

Bartelkeite was detected in voids of germanium ore occurring within dolomites. The mineral associates with galena, germanite, reniérite, and tennantite.

Crystal structure

Bartelkeite is the first analyzed mineral containing both tetrahedrally- and octahedrally-coordinated germanium. It is isostructural with high-pressure form of the silicate lawsonite. In the structure there are:

chains of FeO₆ and GeO₆ octahedra, that share edges
Ge₂O₇ dimers that cross-link the chains
Pb atoms and water molecules in large cavities of the framework