Characterization of minerals and biogeochemical markers on Mars: A Raman and IR spectroscopic study of montmorillonite

Abstract

Raman spectroscopy is likely to be one of a number of instruments deployed to Mars on future landed missions. The goals of these missions will include characterizing the mineralogy of the rocks and soils, in addition to determining if the planet may be or may have been habitable for life. The astrobiology questions are linked to understanding the aqueous and biogeochemical history of Mars. Clay minerals are studied here because if they are found on Mars they may provide information about the geochemistry of the primary rocks and the aqueous history of the planet. This study compares Raman and IR spectra of the SWy-1, STx-1 and SAz-1 montmorillonites. These samples contain admixtures of organic material, carbonate, amorphous silica and fine-grained quartz, which can all be detected using Raman spectroscopy. Less than 0.1 wt% C as organic material was detected in each of the samples through peaks associated with CC or CH bonds. Carbonate was detected in the Raman spectra for the sample containing 1.65 wt% CO3 but not for 0.15 wt% CO3. Raman spectra exhibit unique bands near 200 and 700 cm-1 that are due to tetrahedral SiO 4 in layer silicates and vary depending on the mineral structure. Raman spectra of clay minerals also have unique metal-OH bending vibrations between 840 and 920 cm-1 that provide information about the octahedral cations present. © 2004 John Wiley & Sons, Ltd.