Bartelkeite

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
General
CategoryGermanate mineral
Formula
(repeating unit)		PbFeGe(Ge2O7)(OH)2•H2O
IMA symbolBtk[1]
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[2][3][4]

Occurrence and association

Bartelkeite was detected in voids of germanium ore occurring within dolomites. The mineral associates with galena, germanite, reniérite, and tennantite.[3]

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:[2]

  • 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. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. 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
  3. "Bartelkeite - Handbook of Mineralogy" (PDF). Handbookofmineralogy.org. Retrieved 2016-03-12.
  4. "Bartelkeite: Bartelkeite mineral information and data". Mindat.org. Retrieved 2016-03-04.
  5. 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)
  6. "Mathewrogersite: Mathewrogersite mineral information and data". Mindat.org. Retrieved 2016-03-04.
  7. "Tsumeb Mine (Tsumcorp Mine), Tsumeb, Otjikoto Region (Oshikoto), Namibia - Mindat.org". Mindat.org. Retrieved 2016-03-10.


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