Molecular structure of the mineral woodhouseite CaAl3(PO4,SO4)2(OH)6

The mineral woodhouseite CaAl3(PO4,SO4)2(OH)6 is a hydroxy phosphate-sulphate mineral belonging to the beudantite subgroup of alunites, and has been characterised by Raman spectroscopy, complimented with infrared spectroscopy. Bands at various wavenumbers were assigned to the different vibrational modes of woodhouseite, which were then associated to the molecular 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. Bands in the OH stretching region enabled hydrogen bond distances to be calculated.

► Woodhouseite CaAl3(PO4,SO4)2(OH)6 is a hydroxyl phosphate-sulphate mineral in the beudantite subgroup of aluminites. ► Phosphate and sulphate stretching and bending modes have been assigned and related to the structure of the mineral. ► Two symmetric stretching modes for phosphate and sulphate support the concept of non-equivalent units in the structure. ► Bands in the OH stretching region enabled hydrogen bond distances to be calculated using the Libowitzky empirical function.