Vibrational spectroscopic characterization of the sulphate mineral leightonite K2Ca2Cu(SO4)4·2H2O--implications for the molecular structure.

The mineral leightonite, a rare sulphate mineral of formula K2Ca2Cu(SO4)4·2H2O, has been studied using a combination of electron probe and vibrational spectroscopy. The mineral is characterized by an intense Raman band at 991 cm(-1) attributed to the SO4(2-) ν1 symmetric stretching mode. A series of Raman bands at 1047, 1120, 1137, 1163 and 1177 cm(-1) assigned to the SO4(2-) ν3 antisymmetric stretching modes. The observation of multiple bands shows that the symmetry of the sulphate anion is reduced. Multiple Raman and infrared bands in the OH stretching region shows that water in the structure of leightonite is in a range of molecular environments.