Comparison of the Raman spectra of natural and synthetic K- and Na-jarosites at 298 and 77 K

Raman spectroscopy at 298 and 77 K was used to characterize synthetic and natural jarosites of formula M-2(Fe3+)(6)(SO4)(4)(OH)(12), where M = K or Na. The natural jarosites are characterized by a well-defined hydroxyl stretching pattern, in contrast to that of the synthetic jarosites. This difference is attributed to differences in hydrogen bonding in the mineral. Multiple Raman OH stretching bands are indicative of non-equivalent OH units in the structure. Jarosites are characterized by an intense, sharp band between 1007 and 1010 cm(-1) attributed to the sulfate symmetric stretching mode. The bandwidth for K-jarosite is 4.4 cm(-1) at 298 K and 3.6 cm(-1) at 77 K in comparison with the values for synthetic jarosite of 10.0 (298 K) and 7.3 cm(-1) (77 K). Differences in the spectra between the natural and synthetic jarosites are found. Reasons for these differences in the spectra are provided. Copyright (c) 2005 John Wiley & Sons, Ltd.