Bartelkeite

Bartelkeite
General
Category Germanate mineral
Formula
(repeating unit)
PbFeGe(Ge2O7)(OH)2•H2O
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 ca. 4
Luster Subadamantine
Streak White
Diaphaneity Transparent
Density 4.97 (calculated)
Optical properties Biaxal (-)
Refractive index nα=1.89, nβ=1.91, nγ=1.91 (approximated)
2V angle ca. 35o (measured)
References [1][2][3]

Bartelkeite is an exceptionally rare mineral, one of scarce natural germanium compounds.[3] The formula was originally assumed to be PbFeGe3O8,[4] 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.[1] Bartelkeite and mathewrogersite are minerals with essential (dominant) lead, iron and germanium.[5] Both come from Tsumeb, Namibia - a world's "capital" of germanium minerals.[6]

Occurrence and association

Bartelkeite was detected in voids of germanium ore occurring within dolostones. The mineral associates with galena, germanite, reniérite, and tennantite.[2]

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:[1]

References

  1. 1 2 3 Origlieri, M.J., Yang, H., Downs, R.T., Posner, E.S., Domanik, K.J., and Pinch, W.P., 2012. The crystal structure of bartelkeite, with a revised chemical formula, PbFeGeVI(Ge2IVO7)(OH)2·H2O, isotypic with high-pressure P21/m lawsonite. American Mineralogist 97(10), 1812-1815
  2. 1 2 "Bartelkeite - Handbook of Mineralogy" (PDF). Handbookofmineralogy.org. Retrieved 2016-03-12.
  3. 1 2 "Bartelkeite: Bartelkeite mineral information and data". Mindat.org. Retrieved 2016-03-04.
  4. Keller, V.P., Hess, H., and Dunn, P.J., 1981. Bartelkeit, PbFe2+Ge3O8, ein neues Germanium-Mineral von Tsumeb, Namibia. Chemie der Erde 40, 201-206 (in German)
  5. "Mathewrogersite: Mathewrogersite mineral information and data". Mindat.org. Retrieved 2016-03-04.
  6. "Tsumeb Mine (Tsumcorp Mine), Tsumeb, Otjikoto Region (Oshikoto), Namibia - Mindat.org". Mindat.org. Retrieved 2016-03-10.
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