Hydroniumjarosite, (H3O)+Fe3(SO4)2(OH)6, from Cerros Pintados, Chile: Single-crystal X-ray diffraction and vibrational spectroscopic study. (June 2014)

• Record Type: Journal Article
• Authors: Plášil, J.; Škoda, R.; Fejfarová, K.; Čejka, J.; Kasatkin, A. V.; Dušek, M.; Talla, D.; Lapčák, L.; Machovič, V.; Dini, M.
• Is Part Of: Mineralogical magazine. Volume 78:Number 3(2014:Jun.)
• Page Start: 535
• Page End: 547
• Publication Date: 2014-06
• Subjects: hydroniumjarosite, -- H3O+, -- crystal structure, -- X-ray diffraction, -- vibrational spectroscopy; Mineralogy -- Periodicals; Mineralogy -- Great Britain -- Periodicals; 549.05
• DOI: 10.1180/minmag.2014.078.3.04
• Languages: English
• ISSNs: 0026-461X

Abstract

Abstract: The natural hydroniumjarosite sample from Cerros Pintados (Chile) was investigated by electron microprobe, single-crystal X-ray diffraction and vibrational spectroscopy (Infrared and Raman). The chemical composition of studied specimens (wt.%, mean of seven analyses) obtained from electron microprobe (in wt.%): Na2 O 1.30, K2 O 0.23, CaO 0.04, Fe2 O3 50.49, Al2 O3 0.37, SiO2 0.33, SO3 33.88, H2 O (calculated on the basis of Σ(OH – +H3 O + ) deduced from the charge balance) 13.32, total 99.98, corresponds to the empirical formula (H3 O)0.77 + (Na0.20 K0.02 )∑0.22 (Fe2.95 Al0.03 )∑2.98 (OH)6.12 [(SO4 )1.97 (SiO4 )0.03 ]∑2.00 (calculated on the basis of S + Si = 2 a.p.f.u. (atoms per formula unit)). The studied hydroniumjarosite is trigonal, with space group R m, with a = 7.3408(2), c = 17.0451(6) Å and V = 795.46(4) Å 3 . The refined structure architecture is consistent with known jarosite-series minerals, including synthetic hydroniumjarosite. However, in the current study the presence of H3 O + is well documented in difference Fourier maps, where characteristic positive difference Fourier maxima, with apparent trigonal symmetry, were localized in the vicinity of the O4 atom in the channel-voids of the structure. The structure of natural hydroniumjarosite, including the H atoms, was refined to R 1 = 0.0166 for 2113 unique observed reflections, with I obs >3σ( I ). The present structure model, which includes the position of the H atom within the hydronium ion, is discussed with regard to the vibration spectroscopy results and earlier published density-functional theory (DFT) calculations for the alunite-like structure containing H3 O + .