The reduction of iron(III) oxide minerals is an important component of iron cycling in the subsurface. For example, certain bacteria couple carbon oxidation and iron reduction to obtain energy from growth. Although iron oxides are poor conductors of electricity, electrons that are transfered to an iron oxide mineral are quite mobile, using thermal energy to hop from one iron atom to another. New research used time-resolved X-ray absorption spectroscopy to quantify the hopping rates for different iron(III) mineral phases and to confirm a theoretical picture of how the electron at one site alters the positions of the atoms around it. This work contributes to our understanding of how soil mineralogy evolves when geochemical or biochemical processes create reducing conditions.
(Image courtesy Benjamin Gilbert, Lawrence Berkeley National Laboratory).