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 | |
| 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] |
Occurrence and association
editBartelkeite was detected in voids of germanium ore occurring within dolomites. The mineral associates with galena, germanite, reniérite, and tennantite.[3]
Crystal structure
editBartelkeite 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
edit- ^ 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.
- ^ a b c 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
- ^ a b "Bartelkeite - Handbook of Mineralogy" (PDF). Handbookofmineralogy.org. Retrieved 2016-03-12.
- ^ a b "Bartelkeite: Bartelkeite mineral information and data". Mindat.org. Retrieved 2016-03-04.
- ^ 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)
- ^ "Mathewrogersite: Mathewrogersite mineral information and data". Mindat.org. Retrieved 2016-03-04.
- ^ "Tsumeb Mine (Tsumcorp Mine), Tsumeb, Otjikoto Region (Oshikoto), Namibia - Mindat.org". Mindat.org. Retrieved 2016-03-10.
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