Iron plays a central role in human society and is essential for most living organisms. Iron is the most abundant transition metal in natural environments, occurring mainly in two valence states as oxidized ferric iron Fe(III) and reduced ferrous iron Fe(II). Microorganisms drive the redox transformations of iron from the surface of the Earth down to the depths of the continental and oceanic crusts. Moreover, owing to their metabolic activity and surface properties, microorganisms can mediate the precipitation – and influence the morphology and chemistry – of Fe-containing minerals. For this talk, I will discuss my experimental work that investigate the role of iron oxides in the preservation of microbial cells and structures in rock-forming conditions. The powerful combination of microscopy and spectroscopy allows the characterization of interactions between microbial organic compounds and minerals at the sub-micron scale, furthering our understanding of the impact of microorganisms on global biogeochemical cycles.