Letter: The crystal structure of bartelkeite, with a revised chemical formula, PbFeGe VI(Ge 2 IVO 7) (OH) 2·H 2O, isotypic with high-pressure P2 1/m lawsonite

Marcus J. Origlieri, Hexiong Yang, Robert T. Downs, Esther S. Posner, Kenneth J. Domanik, William W. Pinch

Research output: Contribution to journalArticle

5 Scopus citations

Abstract

Bartelkeite from Tsumeb, Namibia, was originally described by Keller et al. (1981) with the chemical formula PbFeGe 3O 8. By means of electron microprobe analysis, single-crystal X-ray diffraction, and Raman spectroscopy, we examined this mineral from the type locality. Our results show that bartelkeite is monoclinic with space group P2 1/m, unit-cell parameters a = 5.8279(2), b = 13.6150(4), c = 6.3097 (2) Å, β = 127.314(2)°, and a revised ideal chemical formula PbFeGe VIGe 2 IVO 7(OH) 2·H 2O (Z = 2). Most remarkably, bartelkeite is isostructural with the high-pressure P2 1/m phase of lawsonite, CaAl 2Si 2O 7(OH)·H 2O, which is only stable above 8.6 GPa and a potential host for H 2O in subducting slabs. Its structure consists of single chains of edge-sharing FeO 6 and Ge1O 6 octahedra parallel to the c-axis, cross-linked by Ge2 2O 7 tetrahedral dimers. The average <Ge-O> bond lengths for the GeO 6 and GeO 4 polyhedra are 1.889 and 1.744 Å, respectively. The Pb atoms and H 2O groups occupy large cavities within the framework. The hydrogen bonding scheme in bartelkeite is similar to that in lawsonite. Bartelkeite represents the first known mineral containing both 4- and 6-coordinated Ge atoms and may serve as an excellent analog for further exploration of the temperature-pressure-composition space of lawsonite.

Original languageEnglish (US)
Pages (from-to)1812-1815
Number of pages4
JournalAmerican Mineralogist
Volume97
Issue number10
DOIs
StatePublished - Oct 1 2012

Keywords

  • Bartelkeite
  • Crystal structure
  • Germanate
  • Hydrous mineral
  • Raman spectra
  • X-ray diffraction

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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