Raman spectroscopic study of the magnesium-carbonate minerals - artinite and dypingite

Magnesium minerals are important in the understanding of the concept of geosequestration. The two hydrated hydroxy magnesium-carbonate minerals artinite and dypingite were studied by Raman spectroscopy. Intense bands are observed at 1092 cm(-1) for artinite and at 1120 cm(-1) for dypingite, attributed nu(1) symmetric stretching mode of CO32-. The nu(3) antisymmetric stretching vibrations Of CO32- are extremely weak and are observed at 1412 and 1465 cm(-1) for artinite and at 1366, 1447 and 1524 cm(-1) for dypingite. Very weak Raman bands at 790 cm(-1) for artinite and 800 cm(-1) for dypingite are assigned to the CO32- nu(2) out-of-plane bend. The Raman band at 700 cm(-1) of artinite and at 725 and 760 cm(-1) of dypingite are ascribed to CO32- nu(2) in-plane bending mode. The Raman spectrum of artinite in the OH stretching region is characterised by two sets of bands: (1) an intense band at 3593 cm(-1) assigned to the MgOH stretching vibrations and (2) the broad profile of overlapping bands at 3030 and 3229 cm(-1) attributed to water stretching vibrations. X-ray diffraction studies show that the minerals are disordered. This is reflected in the difficulty of obtaining Raman spectra of reasonable quality, and explains why the Raman spectra of these minerals have not been previously or sufficiently described. Copyright (C) 2008 John Wiley & Sons, Ltd.