Crystal-chemistry of sulfates from the Apuan Alps, Tuscany, Italy. VIII. New data on khademite, Al(SO4)F(H2O)5
Open Access
- 30 June 2020
- journal article
- research article
- Published by Mineralogical Society in Mineralogical Magazine
- Vol. 84 (4), 540-546
- https://doi.org/10.1180/mgm.2020.51
Abstract
Khademite, ideally Al(SO4)F(H2O)(3), from the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy, has been characterised through quantitative electron microprobe analysis, micro-Raman spectroscopy and single-crystal X-ray diffraction. Khademite occurs as colourless to whitish tabular crystals, up to 5 mm. Electron microprobe analysis (in wt.%, average of 20 spot analyses) gave: SO3 35.43, Al2O3 21.27, F 6.92, H2Ocalc 39.73, sum 103.35, -O = F 2.92, total 100.43. On the basis of 10 anions per formula unit, assuming the occurrence of 5 H2O groups and 1 (F+OH) atom per formula unit, its chemical formula can b e written as Al0.96S1.02O4[F-0.84(OH)(0.1)(6)](Sigma 1.00)center dot 5H(2)O. The Raman spectrum of khademite is characterised by the occurrence of vibrational modes of SO4 groups and by broad and strong bands due to the O-H stretching modes. Khademite is orthorhombic, space group Pcab, with unit-cell parameters a = 11.1713(2), b = 13.0432(3), c = 10.8815(2) angstrom, V = 1585.54(5) angstrom(3) and Z = 8. The crystal structure refinement converged to R-1 = 0.0293 on the basis of 2359 unique reflections with F-o > 4 sigma(F-o) and 152 refined parameters. The crystal structure of khademite is characterised by the alternation, along b, of two distinct kinds of {010} layers, one formed by [001] rows of isolated Al-centred octahedra, connected to each other through H bonds, and the other showing isolated SO4 groups. Along b, oxygen atoms belonging to SO4 groups act as acceptor of H bonds from H2O groups coordinating Al atoms. The new data improved the description of the H bonds in khademite and led us to discuss about the possible existence of its (OH)-analogue, rostite. In addition, Raman spectroscopic data were collected on the same crystal used for the crystal-chemical characterisation, allowing a comparison with previous results.Keywords
This publication has 28 references indexed in Scilit:
- Vibrational spectroscopic characterization of the sulphate mineral khademite Al(SO4)F⋅5(H2O)Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2013
- Infrared and Raman spectroscopic characterisation of the sulphate mineral creedite – Ca3Al2SO4(F,OH)·2H2O – and in comparison with the alumsSpectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2013
- VOLASCHIOITE, Fe3+4(SO4)O2(OH)6{middle dot}2H2O, A NEW MINERAL SPECIES FROM FORNOVOLASCO, APUAN ALPS, TUSCANY, ITALYThe Canadian Mineralogist, 2011
- A comprehensive spectroscopic study of synthetic Fe2+, Fe3+, Mg2+ and Al3+ copiapite by Raman, XRD, LIBS, MIR and vis–NIRJournal of Raman Spectroscopy, 2010
- Fityk: a general-purpose peak fitting programJournal of Applied Crystallography, 2010
- Secondary sulfate minerals associated with acid drainage in the eastern US: recycling of metals and acidity in surficial environmentsChemical Geology, 2005
- Bond-valence parameters for solidsActa crystallographica Section B, Structural science, crystal engineering and materials, 1991
- Bond valence vs bond length in O...O hydrogen bondsActa crystallographica Section B, Structural science, crystal engineering and materials, 1988
- Bond-valence parameters obtained from a systematic analysis of the Inorganic Crystal Structure DatabaseActa crystallographica Section B, Structural science, crystal engineering and materials, 1985
- Wilcoxite and lannonite, two new fluosulphates from catron county, New MexicoMineralogical Magazine, 1983