Publication details
Hydroniumjarosite, (H3O)Fe-+(3)(SO4)(2)(OH)(6), from Cerros Pintados, Chile: Single-crystal X-ray diffraction and vibrational spectroscopic study
| Authors | |
|---|---|
| Year of publication | 2014 |
| Type | Article in Periodical |
| Magazine / Source | Mineralogical Magazine |
| MU Faculty or unit | |
| Citation | |
| Doi | http://dx.doi.org/10.1180/minmag.2014.078.3.04 |
| Field | Geology and mineralogy |
| Keywords | hydroniumjarosite; H3O+; crystal structure; X-ray diffraction; vibrational spectroscopy |
| Description | 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.%): Na2O 1.30, K2O 0.23, CaO 0.04, Fe2O3 50.49, Al2O3 0.37, SiO2 0.33, SO3 33.88, H2O (calculated on the basis of Sigma(OH-+H3O+) deduced from the charge balance) 13.32, total 99.98, corresponds to the empirical formula (H3O)(0.77)(+)(Na0.20K0.02)(Sigma 0.22)(Fe2.95Al0.03)(Sigma 2.98) (OH)(6.12)[(SO4)(1.97)(SiO4)(0.03)](Sigma 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 (3) over barm, with a = 7.3408(2), c = 17.0451(6) angstrom and V = 795.46(4) angstrom(3). The refined structure architecture is consistent with known jarosite-series minerals, including synthetic hydroniumjarosite. However, in the current study the presence of H3O+ 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>3 sigma(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 H3O+. |