Bartelkeite | |
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General | |
Category | Germanate mineral |
Formula (repeating unit) | PbFeGe(Ge2O7)(OH)2•H2O |
IMA symbol | Btk[1] |
Strunz classification | 9.J0.10 (10 ed) 4/C.08-60 (8 ed) |
Dana classification | 7.6.2.1 |
Crystal system | Monoclinic |
Crystal class | Spheroidal (2) or prismatic (2/m) |
Space group | P21 or P21/m |
Unit cell | a = 5.83, b = 13.62, c = 6.31 [Å], β = 127.31° (approximated); Z = 2 |
Identification | |
Color | Colorless, white, very pale greenish |
Crystal habit | tabular; acicular |
Cleavage | {101}, distinct |
Mohs scale hardness | 4 |
Luster | Subadamantine |
Streak | White |
Diaphaneity | Transparent |
Density | 4.97 |
Optical properties | Biaxal (-) |
Refractive index | nα=1.89, nβ=1.91, nγ=1.91 (approximated) |
2V angle | ca. 35o (measured) |
References | [2][3][4] |
Bartelkeite is an exceptionally rare mineral, one of scarce natural germanium compounds.[4] The formula was originally assumed to be PbFeGe3O8,[5] 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.[2] Bartelkeite and mathewrogersite are minerals with essential (dominant) lead, iron and germanium.[6] Both come from Tsumeb, Namibia - a world's "capital" of germanium minerals.[7]
Bartelkeite was detected in voids of germanium ore occurring within dolomites. The mineral associates with galena, germanite, reniérite, and tennantite.[3]
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:[2]