The mixed anion mineral chalcophyllite Cu 18 Al 2 (AsO 4 ) 4 (SO 4 ) 3 (OH) 24 ·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 ∼814 cm −1 are assigned to the ν 1 (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.
The mineral xocomecatlite is a hydroxy metatellurate mineral with Te 6+ O 4 units. Tellurates may be subdivided according to their formula into three types of tellurate minerals: type (a) (AB) m (TeO 4 ) p Z q , type (b) (AB) m (TeO 6 ) · xH 2 O and (c) compound tellurates in which a second anion including the tellurite anion, is involved. The mineral xocomecatlite is an example of the first type. Raman bands for xocomecatlite at 710, 763 and 796 cm −1 , and 600 and 680 cm −1 are attributed to the ν 1 (TeO 4 ) 2− symmetric and ν 3 antisymmetric stretching mode. Raman bands observed at 2867 and 2926 cm −1 are assigned to TeOH stretching vibrations and enable estimation of the hydrogen bond distances of 2.622 Å (2867 cm −1 ), 2.634 Å (2926 cm −1 ) involving these OH units. The hydrogen bond distances are very short implying that they are necessary for the stability of the mineral.
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