The spectroscopic characterization of the sulphate mineral ettringite from Kuruman manganese deposits, South Africa.

The mineral ettringite has been studied using a number of techniques, including XRD, SEM with EDX, thermogravimetry and vibrational spectroscopy. The mineral proved to be composed of 53% of ettringite and 47% of thaumasite in a solid solution. Thermogravimetry shows a mass loss of 46.2% up to 1000 ?C. Raman spectroscopy identifies multiple sulphate symmetric stretching modes in line with the three sulphate crystallographically different sites. Raman spectroscopy also identifies a band at 1072 cm?1 attributed to a carbonate symmetric stretching mode, confirming the presence of thaumasite. The observation of multiple bands in the _4 spectral region between 700 and 550 cm?1 offers evidence for the reduction in symmetry of the sulphate anion from Td to C2v or even lower symmetry. The Raman band at 3629 cm?1 is assigned to the OH unit stretching vibration and the broad feature at around 3487 cm?1 to water stretching bands. Vibrational spectroscopy enables an assessment of the molecular structure of natural ettringite to be made