Dussertite BaFe(3)(3+)(AsO(4))(2)(OH)(5) - a Raman spectroscopic study of a hydroxy-arsenate mineral
Abstrakt
The mineral dussertite, a hydroxy-arsenate mineral with formula BaFe3(AsO4)2(OH)5, has been studied by Raman spectroscopy complemented with infrared spectroscopy. The spectra of three minerals from different origins were investigated and proved to be quite similar, although some minor differences were observed.
In the Raman spectra of the Czech dussertite, four bands are observed in the 800-950 cm-1 region. The bands are assigned as follows: the band at 902 cm-1 is assigned to the (AsO4)3- v3 antisymmetric stretching mode, the one at 870 cm-1 to the (AsO4)3- v1 symmetric stretching mode, and those at 859 and 825 cm-1 to the As-OM2+/3+ stretching modes and/or hydroxyl bending modes.
Raman bands at 372 and 409 cm-1 are attributed to the v2 (AsO4)3- bending mode and the two bands at 429 and 474 cm-1 are assigned to the v4 (AsO4)3- bending mode. An intense band at 3446 cm-1 in the infrared spectrum and a complex set of bands centred upon 3453 cm-1 in the Raman spectrum are attributed to the stretching vibrations of the hydrogen-bonded (OH)- units and/or water units in the mineral structure.
The broad infrared band at 3223 cm-1 is assigned to the vibrations of hydrogen-bonded water molecules.