Raman microscopy of selected autunite minerals
Frost, Ray L.; Weier, Matt
published: Nov 29, 2004
Raman spectroscopy at ambient and liquid nitrogen temperature has been used to determine the molecular structure of selected minerals from the autunite and meta-autunite groups. Six hydroxyl stretching bands for autunite are observed of which three are highly polarised. The hydroxyl stretching vibrations are related to the strength of hydrogen bonding of the water units. Bands in the Raman spectrum of autunite at 998, 842 and 820 cm1 are highly polarised. Low intensity band at 915 cm1 is attributed to the ν3 antisymmetric stretching vibration of (UO2)2+ units. The band at 820 cm1 is attributed to the ν1 symmetric stretching mode of the (UO2)2+ units. The (UO2)2+ bending modes are found at 295 and 222 cm1. The presence of phosphate and arsenate anions and their isomorphic substitution are readily determined by Raman spectroscopy. The collection of Raman spectra at 77 K enables excellent band separation.