Experimental and theoretical XANES and EXAFS study of tetra-ferriphlogopite

Experimental and theoretical EXAFS and XANES data on Fe coordination and bo nd distances have been obtained for a natural tetra-ferriphlogopite. XANES data show a predominance of trivalent iron in tetrahedral coordination. The use of theoretical multiple scattering calculations helps distinguish the contributions to the total spectrum coming from the different iron atoms. E XAFS spectra were reduced and analyzed using the GNXAS programs and Fe has been confirmed to be in tetrahedral coordination, with refined structural d ata Fe-O = 1.86 Angstrom, Fe-Si = 3.24 Angstrom, Fe-O-Si = 138 degrees. Mor eover, a further contribution from Fe is detected corresponding to a Fe-O d istance equal to 2.22 Angstrom. This latter contribution (20 mol % of the t otal Fe ca.) is interpreted to arise from divalent Fe in octahedral coordin ation, in excellent agreement with the structural and chemical data.