A vibrational spectroscopic study of the mineral corkite PbFe33+ (PO4,SO4)2(OH)6

The mineral corkite PbFe33+(PO4,SO4)2(OH)6 is a hydroxy phosphate mineral belonging to the beudantite subgroup of alunites. The mineral has been characterised by Raman spectroscopy and infrared spectroscopy. Bands at various wavenumbers were assigned to the different vibrational modes of corkite, which were then associated to the structure of the mineral. Bands were primarily assigned to phosphate and sulphate stretching and bending modes. Two symmetric stretching modes for both phosphate and sulphate supported the concept of non-equivalent phosphate and sulphate units in the mineral structure. Broad bands in the OH stretching region enabled hydrogen bond distances to be calculated.