Bartelkeite

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]

Bartelkeite
General
CategoryGermanate mineral
Formula
(repeating unit)		PbFeGe(Ge2O7)(OH)2•H2O
Strunz classification9.J0.10 (10 ed)
4/C.08-60 (8 ed)
Dana classification7.6.2.1
Crystal systemMonoclinic
Crystal classSpheroidal (2) or prismatic (2/m)
Space groupP21 or P21/m
Unit cella = 5.83, b = 13.62, c = 6.31 [Å], β = 127.31° (approximated); Z = 2
Identification
ColorColorless, white, very pale greenish
Crystal habittabular; acicular
Cleavage{101}, distinct
Mohs scale hardness4
LusterSubadamantine
StreakWhite
DiaphaneityTransparent
Density4.97
Optical propertiesBiaxal (-)
Refractive indexnα=1.89, nβ=1.91, nγ=1.91 (approximated)
2V angleca. 35o (measured)
References[1][2][3]

Occurrence and association

Bartelkeite was detected in voids of germanium ore occurring within dolomites. 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]

  • 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

References
  1. 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. "Bartelkeite - Handbook of Mineralogy" (PDF). Handbookofmineralogy.org. Retrieved 2016-03-12.
  3. "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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