Bartelkeite
| Bartelkeite | |
|---|---|
| General | |
| Category | Germanate mineral |
| Formula (repeating unit) | PbFeGe(Ge2O7)(OH)2•H2O |
| Strunz classification | 4/C.08-60 |
| Dana classification | 7.6.2.1 |
| Crystal system | Monoclinic, space group P21/m |
| Unit cell | a=5.83, b=13.62, c=6.31 [Å], β=127.31o (approximated) |
| Identification | |
| Color | Colorless, white, very pale greenish |
| Crystal habit | tabular; acicular |
| Crystal symmetry | Monoclinic - Prismatic (2/m) |
| 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]
- 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 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
- 1 2 "Bartelkeite - Handbook of Mineralogy" (PDF). Handbookofmineralogy.org. Retrieved 2016-03-12.
- 1 2 "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.