Raman spectroscopic study of the hydroxy-arsenate-sulfate mineral chalcophyllite Cu_(18)Al_2(AsO_4)_4(SO_4)_3(OH)_(24)·36H_2O

摘要

The mixed anion mineral chalcophyllite Cu_(18)Al_2(AsO_4)_4(SO_4)_3(OH)_(24)·36H_2O 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 ～814 cm~(?1) are assigned to the ν1 (AsO_4)~(3?) symmetric stretching and ν_3 (AsO_4)~(3?) antisymmetric stretching modes. The comparatively sharp band at 980 cm?1 is assigned to the ν_1 (SO_4)~(2?) symmetric stretching mode, and a broad spectral profile centred upon 1100 cm~(?1) is attributed to the ν_3 (SO_4)~(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.