Raman and FTIR spectroscopy of natural oxalates: Implications for the evidence of life on Mars

Evidence for the existence of primitive life forms such as lichens and fungi can be based upon the formation of oxalates. Oxalates are most readily detected using Raman spectroscopy. A comparative study of a suite of natural oxalates including weddellite, whewellite, moolooite, humboldtine, glushinskite, natroxalate and oxammite has been undertaken using Raman spectroscopy. The minerals are characterised by the Raman position of the CO stretching vibration which is cation sensitive. The band is observed at 1468 cm-1 for weddellite, 1489 cm-1 for moolooite, 1471 cm-1 for glushinskite and 1456 cm-1 for natroxalate. Except for oxammite, the infrared and Raman spectra are mutually exclusive indicating the minerals are bidentate. Differences are also observed in the water OH stretching bands of the minerals. 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.