bartelkeite

{{infobox mineral | name = Bartelkeite | category = Germanate mineral | image = | imagesize = | alt = | caption = | formula = PbFeGe(Ge2O7)(OH)2•H2O |IMAsymbol=Btk | strunz = 9.J0.10 (10 ed) 4/C.08-60 (8 ed) | dana = 7.6.2.1 | system = Monoclinic | class = Spheroidal (2) or prismatic (2/m) | symmetry = P21 or P21/m | unit cell = a = 5.83, b = 13.62, c = 6.31 [Å], β = 127.31° (approximated); Z = 2 | color = Colorless, white, very pale greenish | colour = | habit = tabular; acicular | twinning = | cleavage = {101}, distinct | fracture = | tenacity = | mohs = 4 | luster = Subadamantine | streak = White | diaphaneity = Transparent | gravity = | density = 4.97 | polish = | opticalprop = Biaxal (-) | refractive = nα=1.89, nβ=1.91, nγ=1.91 (approximated) | birefringence = | pleochroism = | 2V = ca. 35o (measured) | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | references = }} 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 PbFeGe(Ge2O7)(OH)2•H2O. 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.