Funnell, Nicholas P.Fulford, Maxwell F.Inoue, SayakoKletetschka, KarelMichel, F. MarcGoodwin, Andrew L.2020-05-152020-05-152020-02-212399-366922http://hdl.handle.net/10919/98402Ferrihydrite is one of the most important iron-containing minerals on Earth. Yet determination of its atomic-scale structure has been frustrated by its intrinsically poor crystallinity. The key difficulty is that physically-different models can appear consistent with the same experimental data. Using X-ray total scattering and a nancomposite reverse Monte Carlo approach, we evaluate the two principal contending models-one a multi-phase system without tetrahedral iron(III), and the other a single phase with tetrahedral iron(III). Our methodology is unique in considering explicitly the complex nanocomposite structure the material adopts: namely, crystalline domains embedded in a poorly-ordered matrix. The multi-phase model requires unphysical structural rearrangements to fit the data, whereas the single-phase model accounts for the data straightforwardly. Hence the latter provides the more accurate description of the short- and intermediate-range order of ferrihydrite. We discuss how this approach might allow experiment-driven (in)validation of complex models for important nanostructured phases beyond ferrihydrite. Although a geologically important mineral, the atomic-scale structure of ferrihydrite remains unresolved. Here the authors combine X-ray total scattering and reverse Monto Carlo to evaluate the two principal contending models, explicitly considering the material's complex nanocomposite structure.application/pdfenCreative Commons Attribution 4.0 InternationalArticle - Refereedhttps://doi.org/10.1038/s42004-020-0269-231