GIXAFS study of Fe3+ sorption and precipitation on natural quartz surfaces

Grazing-incidence EXAFS has been used to characterize the structure of Fe³⁺ sorbed onto natural single crystal quartz surfaces. Fe³⁺ sorption at ca. 5% monolayer coverage on a natural crystal allowed to equilibrate in air resulted in formation of hematite nuclei with strong texturing on r-and m-planes. EXAFS calculations suggests that both O and Fe backscattering is necessary to yield acceptable structural models, that about 50% of the sorbed iron resides in nuclei, and that the approximate dimensions of the nuclei can be estimated via Feff 7.0 calculations of various nuclei sizes and shapes.