Crystal chemistry of the tsumcorite-group minerals
- Author(s)
- Werner Krause, Klaus Belendorff, Heinz-Jürgen Bernhardt, Catherine McCammon, Herta Silvia Effenberger, Werner Mikenda
- Abstract
Optical properties, morphol., chem. compn., IR and Moessbauer spectroscopy, and crystal structure of the title minerals were investigated. Crystal symmetry is either triclinic in the case of an ordered occupation of two Me(2) sites, triclinic due to ordering of the H bonds in the case of species with 2 water mols. per formula unit, or monoclinic in the other cases. Cell parameters were refined from x-ray powder data; powder patterns are given for thometzekite (sulfatian), mounanaite, helmutwinklerite, gartrellite and zincian gartrellite. Mossbauer measurements confirmed the Fe in ferrilotharmeyerite, tsumcorite, gartrellite and zincian gartrellite to be completely trivalent. Electron microprobe analyses showed that at least partial solid soln. is common for the Me(2) and less frequent for the X and Me(1) site. In addn. to homovalent substitutions there are 3 heterovalent exchange mechanisms with a coupled substitution involving OH/H2O groups. Crystals of ferrilotharmeyerite, tsumcorite, thometzekite (sulfatian), and mounanaite have monoclinic symmetry, space group C2/m. The crystal structures were investigated by single-crystal x-ray diffraction. The structural data for tsumcorite given by Tillmanns & Gebert (1973) were confirmed, for the other minerals isotypy is proved. IR absorption spectra indicate 2 independent and strong H bonds. There is no evidence for protonated arsenate groups. The chem. formulas of ferrilotharmeyerite and lotharmeyerite (for analogy reasons) have to be revised on a 10 O basis to Ca(Fe3+,Zn)2(AsO4)2(OH,H2O)2, and Ca(Mn3+,Zn)2 (AsO4)2(OH,H2O)2, resp. The triclinic members of the tsumcorite group are gartrellite, zincian gartrellite, phosphogartrellite, helmutwinklerite, and probably (sulfate-free) thometzekite; the space group is P&1, with a pronounced monoclinic C-centered pseudocell. A redefinition based on type material was performed for gartrellite; it has the ideal formula PbCuFe3+(AsO4)2(OH)(H2O), but it frequently contains substantial amts. of Zn (at least up to 12.6 wt% ZnO), whereas the ratio Cu:Fe is close to 1:1. The triclinic distortion is caused by an ordered arrangement of Fe[6]O6 octahedra and tetragonal bi-pyramidal Cu[4+2]O6 polyhedra, as shown by Rietveld refinement of powder data. The weak superstructure reflections of helmutwinklerite obsd. by single-crystal x-ray investigations are obviously caused by an ordering of the H bonds.
- Organisation(s)
- Department of Mineralogy and Crystallography, Department of Organic Chemistry
- External organisation(s)
- Ruhr-Universität Bochum (RUB), Universität Bayreuth
- Journal
- European Journal of Mineralogy: an international journal of mineralogy, geochemistry and related sciences
- Volume
- 10
- Pages
- 179-206
- No. of pages
- 28
- ISSN
- 0935-1221
- DOI
- https://doi.org/10.1127/ejm/10/2/0179
- Publication date
- 03-1998
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105113 Crystallography, 105116 Mineralogy, 104026 Spectroscopy
- Keywords
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/crystal-chemistry-of-the-tsumcoritegroup-minerals(96a2308b-d720-4cb2-9400-bcd6b875c717).html