Raman and infrared spectroscopic characterization of the phosphate mineral paravauxite Fe2+Al2(PO4)2(OH)2. 8H2O.

Abstract

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+0,95; (Al0:07)R1:02ðAlÞ2:09ðPO4Þ1:97ðOHÞ1:98.7:90(H2O).The Raman spectrum is dominated by an intense Raman band at 1020 cm^-1assigned to the PO4^-3 m1symmetric stretching mode. Low intensity Raman bands found at 1058, 1115 and 1148 cm^-1 are assigned to the PO4^-3 m3 antisymmetric stretching vibrations. Raman bands of paravauxite at 537, 570, 609 and 643 cm^-1 are assigned to the m4 PO4^-3 bending modes whilst the Raman bands at 393 and 420 cm^-1are due to the m2 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.