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

Jakub Plasil (Korresp. Autor*in), Radek Skoda, K. Fejfarová, J. Cejka, A.V. Kasatkin, M. Dusek, Dominik Talla, L. Lapčák, V. Machovic, M. Dini

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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.%): Na 2O 1.30, K 2O 0.23, CaO 0.04, Fe 2O 3 50.49, Al 2O 3 0.37, SiO 2 0.33, SO 3 33.88, H 2O (calculated on the basis of ∑(OH -+H 3O +) deduced from the charge balance) 13.32, total 99.98, corresponds to the empirical formula (H 3O) 0.77 +(Na 0.20K 0.02) S 0.22(Fe 2.95Al 0.03)∑ 2.98 (OH) 6.12[(SO 4) 1.97(SiO 4) 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 R3̄m, 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 H 3O + 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 H 3O +.

Seiten (von - bis)535-547
FachzeitschriftMineralogical Magazine
PublikationsstatusVeröffentlicht - 1 Juni 2014

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