We have undertaken a vibrational spectroscopic study of paravauxite the Siglo XX mine, Bustillo Province, northern of Potosí department, Bolivia. This mine is important source for rare and unusual secondary phosphate minerals and is the type locality for a number of rare phosphates such as vauxite, sigloite, metavauxite and for jeanbandyite. The chemical formula of the studied sample was determined as Fe(2+)(0.9)5, Al(0.07)Σ1.02 (Al)2.09 (PO4)1:97 (OH)1.98 · 7.90(H2O). The Raman spectrum is dominated by an intense Raman band at 1020 cm(-1) assigned to the PO4(3-) ν1 symmetric stretching mode. Low intensity Raman bands found at 1058, 1115 and 1148 cm(-1) are assigned to the PO4(3-) ν3 antisymmetric stretching vibrations. Raman bands of paravauxite at 537, 570, 609 and 643 cm(-1) are assigned to the ν4 PO4(3-) bending modes whilst the Raman bands at 393 and 420 cm(-1) are due to the ν2 PO4(3-) bending modes. The Raman spectral profile of paravauxite in the hydroxyl stretching region is broad with component bands resolved at 3086, 3215, 3315, 3421, 3505 and 3648 cm(-1). Vibrational spectroscopy enables the assessment of the molecular structure of paravauxite to be undertaken.

The molecular structure of the arsenate mineral ceruleite has been assessed using a combination of Raman and infrared spectroscopy. The most intense band observed at 903 cm(-1) is assigned to the (AsO4)(3-) symmetric stretching vibrational mode. The infrared spectrum shows intense bands at 787, 827 and 886 cm(-1), ascribed to the triply degenerate ν3 antisymmetric stretching vibration. Raman bands observed at 373, 400, 417 and 430 cm(-1) are attributed to the ν2 vibrational mode. Three broad bands for ceruleite found at 3056, 3198 and 3384 cm(-1) are assigned to water OH stretching bands. By using a Libowitzky empirical equation, hydrogen bond distances of 2.65 and 2.75Å are calculated. Vibrational spectra enable the molecular structure of the ceruleite mineral to be determined and whilst similarities exist in the spectral patterns with the roselite mineral group, sufficient differences exist to be able to determine the identification of the minerals.

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