title: Bartelkeite
text: # Bartelkeite
  
  Bartelkeite is an exceptionally rare mineral, one of scarce natural germanium compounds. The formula was originally assumed to be $PbFeGe_3O_8,$ bartelkeite was later shown to be isostructural with a high-pressure form of the mineral lawsonite. Thus, its correct formula is $PbFeGe(Ge_2O_7)(OH)_2•H_2O.$ Bartelkeite and mathewrogersite are minerals with essential (dominant) 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 $FeO_6$ and $GeO_6$ octahedra, that share edges
  * $Ge_2O_7$ dimers that cross-link the chains
  * Pb atoms and water molecules in large cavities of the framework
  