In situ infrared spectroscopic studies of OH, H2O and CO2 in moganite at high temperatures

The thermal stabilities of OH and H2O in moganite from the Mogan D formation, Gran Canaria have been investigated during heating and cooling using in situ Fourier transform infrared spectroscopy. The spectra have also been analysed in terms of CO2 incorporated in moganite. The results show that while the thermal responses of H2O and OH in moganite display similarities to those reported in agate, the spectra are not completely identical. Absorptions in the O-H stretching region reveal that dehydration and dehydroxylation is a multi-stage process. Although hydrogen loss starts below 400-500 K, hydrous species may well remain in moganite even at 1060 K. After cooling, the spectra of multiphonon bands from lattice vibrations in a moganite sample that had been heated up to 1060 K became similar to those of agate implying a moganite to alpha-quartz transformation can be thermally induced. CO2 was first detected at temperatures similar to 460 K. However, a further increase in CO2 absorption has been identified around 940 K, and this is probably associated with the decomposition of CO3.