Raman spectroscopic study of the mineral arsenogorceixite BaAl₃AsO₃(OH)(AsO₄,PO₄)(OH,F)₆

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• 作者：Ray L. Frost^a ; ^{r.frost@qut.edu.au} ; Yunfei Xi^a ; Ross E. Pogson^b
• 关键词：Arsenogorceixite ; Gorceixite ; Arsenate ; Phosphate ; Crandallite ; Raman spectroscopy
• 刊名：Spectrochimica Acta Part A ; Molecular and Biomolecular Spectroscopy
• 出版年：2012
• 期刊代码：99_13861425
• 类别：ch
• 出版时间：June, 2012
• 卷：91
• 期：Complete
• 页码：301-306
• 文件大小：735 K

摘要

Arsenogorceixite BaAl₃AsO₃(OH)(AsO₄,PO₄)(OH,F)₆ belongs to the crandallite mineral subgroup of the alunite supergroup. Arsenogorceixite forms a continuous series of solid solutions with related minerals including gorceixite, goyazite, arsenogoyazite, plumbogummite and philipsbornite. Two minerals from (a) Germany and (b) from Ashburton Downs, Australia were analysed by Raman spectroscopy. The spectra show some commonality but the intensities of the peaks vary.

Sharp intense Raman bands for the German sample, are observed at 972 and 814 cm^鈭? attributed to the 谓₁ PO₄^{3鈭?/sup> and AsO₄3鈭?/sup> symmetric stretching modes. Raman bands at 1014, 1057, 1148 and 1160 cm鈭? are attributed to the 谓₁ PO₂ symmetric stretching mode and 谓₃ PO₄3鈭?/sup> antisymmetric stretching vibrations. Raman bands at 764 and 776 cm鈭? and 758 and 756 cm鈭? are assigned to the 谓₃ AsO₄3鈭?/sup> antisymmetric stretching vibrations. For the Australian mineral, the 谓₁ PO₄3鈭?/sup> band is found at 973 cm鈭?. The intensity of the arsenate bands observed at 814, 838 and 870 cm鈭? is greatly enhanced.}

Two low intensity Raman bands at 1307 and 1332 cm^鈭? are assigned to hydroxyl deformation modes. The intense Raman band at 441 cm^鈭? with a shoulder at 462 cm^鈭? is assigned to the 谓₂ PO₄^{3鈭?/sup> bending mode. Raman bands at 318 and 340 cm鈭? are attributed to the (AsO₄)3鈭?/sup> 谓₂ bending. The broad band centred at 3301 cm鈭? is assigned to water stretching vibrations and the sharper peak at 3473 cm鈭? is assigned to the OH stretching vibrations. The observation of strong water stretching vibrations brings into question the actual formula of arsenogorceixite. It is proposed the formula is better written as BaAl₃AsO₃(OH)(AsO₄,PO₄)(OH,F)₆路xH₂O. The observation of both phosphate and arsenate bands provides a clear example of solid solution formation.}