Raman and infrared spectroscopic characterization of the arsenate-bearing mineral tangdanite- and in comparison with the discredited mineral clinotyrolite

The minerals clinotyrolite and fuxiaotuite are discredited in terms of the mineral tangdanite. The mixed anion mineral tangdanite Ca2Cu9(AsO4)(4)(SO4)(0.5)(OH)(9) 9H(2)O has been studied using a combination of Raman and infrared spectroscopy. Characteristic bands associated with arsenate, sulphate and hydroxyl units are identified. Broad bands in the OH stretching region are observed and are resolved into component bands. These bands are assigned to water and hydroxyl stretching vibrations. Two intense Raman bands at 837 and approximately 734cm(-1) are assigned to the (1) (AsO4)(3-) symmetric stretching and (3) (AsO4)(3-) antisymmetric stretching modes. Infrared bands at 1023cm(-1) are assigned to the (SO4)(2-) (1) symmetric stretching mode, and infrared bands at 1052, 1110 and 1132cm(-1) assigned to (SO4)(2-) (3) antisymmetric stretching modes, confirming the presence of the sulphate anion in the tangdanite structure. Raman bands at 593 and 628cm(-1) are attributed to the (SO4)(2-) (4) bending modes. Low-intensity Raman bands found at 457 and 472cm(-1) are assigned to the (AsO4)(3-) (2) bending modes. A comparison is made with the previously obtained spectral data on the discredited mineral clinotyrolite. Copyright (c) 2015 John Wiley & Sons, Ltd.