Biological modification of haematite in Antarctic cryptoendolithic communities

Detailed FT-Raman spectra of Antarctic cryptoendolithic colonies in Beacon sandstone have revealed some novel information about the biogeological modification process involving iron(III) mobilization by the organism. The previously unreported but characteristic orange-yellow surface colour of endolithic rock specimens is attributed to the presence of goethite, alpha-FeOOH, iron(III) oxide hydroxide, which has been converted from haematite, alpha-Fe2O3, by cyanobacterial modification. Although goethite is also identified in the biological layers, haematite is found unchanged elsewhere in the specimens. No spectroscopic evidence is found for iron(III) complexes of metabolic byproducts such as oxalate or pyruvate. The results are of relevance to remote spectroscopic sensing experiments for Martian planetary surface exploration, where the presence of iron(III) oxide is evident, below which it seems likely that a significant quantity of hydroxyl groups in the form of water could exist.