Raman spectroscopic study of the hydroxy-arsenate-sulfate mineral chalcophyllite Cu18Al2(AsO4)4(SO4)3(OH)24•36H2O

The mixed anion mineral chalcophyllite Cu18Al2(AsO4)(4)(SO4)(3)(OH)(24)center dot 36H(2)O has been studied by using Raman and infrared spectroscopies. Characteristic bands associated with arsenate, sulfate and hydroxyl units are identified. Broad bands in the OH stretching region are observed and are resolved into component bands. Estimates of hydrogen bond distances were made using a Libowitzky function. Both short and long hydrogen bonds were identified. Two intense bands at 841 and similar to 814 cm(-1) are assigned to the v(1) (AsO4)(3-) symmetric stretching and v(3) (AsO4)(3-) antisymmetric stretching modes. The comparatively sharp band at 980 cm(-1) is assigned to the v(1) (SO4)(2-) symmetric stretching mode, and a broad spectral profile centred upon 1100 cm(-1) is attributed to the v(3) (SO4)(2-) antisymmetric stretching mode. A comparison of the Raman spectra is made with other arsenate-bearing minerals such as carminite, clinotyrolite, kankite, tilasite and pharmacosiderite. Copyright (C) 2010 John Wiley & Sons, Ltd.