Raman spectroscopy of natural oxalates at 298 and 77 K

A comparative study of a suite of natural oxalates including weddellite, whewellite, moolooite, humboldtine, glushinskite, natroxalate and oxammite was undertaken using Raman spectroscopy at 298 and 77 K. Oxalates are found as films on host rocks as a result of heavy metal expulsion by primitive plants such as lichens and fungi. The minerals are characterized by the Raman position of the CO stretching vibration, which is cation sensitive. The band is observed at 1468 cm(-1) for weddellite, 1464 cm(-1) for whewellite, 1489 cm(-1) for moolooite, 1489 cm(-1) for humboldtine, 1471 cm(-1) for glushinskite, 1456 cm(-1) for natroxalate and 1473 cm(-1) for oxammite. Except for oxammite, the infrared and Raman spectra are mutually exclusive, indicating that the minerals are bidentate and planar. Significant differences are observed in the CC stretching region and in the OCO bending region centred upon 910 and 860 cm(-1), respectively. The significance of this work rests with the ability of Raman spectroscopy to identify oxalates which often occur as a film on a host rock. As such, Raman spectroscopy has the potential to identify the existence or pre-existence of life forms on planets such as Mars. Copyright (C) 2003 John Wiley Sons, Ltd.