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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2018: 2.631

CiteScore 2018: 2.55

SCImago Journal Rank (SJR) 2018: 1.355
Source Normalized Impact per Paper (SNIP) 2018: 1.103

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1945-3027
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Volume 97, Issue 10

Issues

Letter. The crystal structure of bartelkeite, with a revised chemical formula, PbFeGeVI(Ge2 IVO7) (OH)2·H2O, isotypic with high-pressure P21/m lawsonite

Marcus J. Origlieri / Hexiong Yang / Robert T. Downs / Esther S. Posner / Kenneth J. Domanik / William W. Pinch
Published Online: 2015-04-02 | DOI: https://doi.org/10.2138/am.2012.4269

Abstract

Bartelkeite from Tsumeb, Namibia, was originally described by Keller et al. (1981) with the chemical formula PbFeGe3O8. 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 P21/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 PbFeGeVIGe2IVO7(OH)2·H2O (Z = 2). Most remarkably, bartelkeite is isostructural with the high-pressure P21/m phase of lawsonite, CaAl2Si2O7(OH)·H2O, which is only stable above 8.6 GPa and a potential host for H2O in subducting slabs. Its structure consists of single chains of edge-sharing FeO6 and Ge1O6 octahedra parallel to the c-axis, cross-linked by Ge22O7 tetrahedral dimers. The average <Ge-O> bond lengths for the GeO6 and GeO4 polyhedra are 1.889 and 1.744 Å, respectively. The Pb atoms and H2O 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.

Keywords : Bartelkeite; germanate; hydrous mineral; crystal structure; X-ray diffraction; Raman spectra

About the article

Received: 2012-06-19

Accepted: 2012-07-15

Published Online: 2015-04-02

Published in Print: 2012-10-01


Citation Information: American Mineralogist, Volume 97, Issue 10, Pages 1812–1815, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am.2012.4269.

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© 2015 by Walter de Gruyter Berlin/Boston.Get Permission

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