The mixed anion mineral parnauite Cu9[(OH)10|SO4|(AsO4)2]·7H2O--a Raman spectroscopic study.

The mixed anion mineral parnauite Cu(9)[(OH)(10)|SO(4)|(AsO(4))(2)]·7H(2)O from two localities namely Cap Garonne Mine, Le Pradet, France and Majuba Hill mine, Pershing County, Nevada, USA has been studied by Raman spectroscopy. The Raman spectrum of the French sample is dominated by an intense band at 975 cm(-1) assigned to the ν(1) (SO(4))(2-) symmetric stretching mode and Raman bands at 1077 and 1097 cm(-1) may be attributed to the ν(3) (SO(4))(2-) antisymmetric stretching mode. Two Raman bands 1107 and 1126 cm(-1) are assigned to carbonate CO(3)(2-) symmetric stretching bands and confirms the presence of carbonate in the structure of parnauite. The comparatively sharp band for the Pershing County mineral at 976 cm(-1) is assigned to the ν(1) (SO(4))(2-) symmetric stretching mode and a broad spectral profile centered upon 1097 cm(-1) is attributed to the ν(3) (SO(4))(2-) antisymmetric stretching mode. Two intense bands for the Pershing County mineral at 851 and 810 cm(-1) are assigned to the ν(1) (AsO(4))(3-) symmetric stretching and ν(3) (AsO(4))(3-) antisymmetric stretching modes. Two Raman bands for the French mineral observed at 725 and 777 cm(-1) are attributed to the ν(3) (AsO(4))(3-) antisymmetric stretching mode. For the French mineral, a low intensity Raman band is observed at 869 cm(-1) and is assigned to the ν(1) (AsO(4))(3-) symmetric stretching vibration. Chemical composition of parnauite remains open and the question may be raised is parnauite a solid solution of two or more minerals such as a copper hydroxy-arsenate and a copper hydroxy sulphate.