Publication Date:
2014-07-25
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.%): Na 2 O 1.30, K 2 O 0.23, CaO 0.04, Fe 2 O 3 50.49, Al 2 O 3 0.37, SiO 2 0.33, SO 3 33.88, H 2 O (calculated on the basis of (OH – +H 3 O + ) deduced from the charge balance) 13.32, total 99.98, corresponds to the empirical formula $${\left({\mathrm{H}}_{3}\mathrm{O}\right)}_{0.77}^{+}$$ (Na 0.20 K 0.02 ) 0.22 (Fe 2.95 Al 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 R 3I 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 H 3 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 〉3( 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 3 O + .
Print ISSN:
0026-461X
Electronic ISSN:
1471-8022
Topics:
Geosciences
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