Distinction of jarosite-group compounds by Raman spectroscopy

Abstract

Raman spectra (200-1300 cm-I) were measured for synthesized jarosite-group compounds [MFe,(S04h(OH)r M+ = K+, NH4+,Na+, Ag+, and Y2Pb2+).The Raman spectra of jarosite-group compounds are characterized by a tendency for the wavenumbersassigned to two vibrational modes of S042-, VI(SOi-) and vj(SOi-), and three vibrational modes of Fe-O bonds, to decrease with increase in the c unit-cell parameter. The wavenumbers assigned to the v2(SOi-) and v4(SOi-) vibrational modes'are independent of the.value.of c. For plumbojarosite, thc peaks corresponding to the VI(S042-) and V,(S042-) vibrational modesare broad owing to two overlapping peaks assigned to two types of sulfate groups, S042- ions adjacent and not adjacent to Pb2+ ions. Raman spectra can serve to identify the specific type of jarosite-group compound in poorly crystalline or low-concentration geochemical samples.