AN XAFS STUDY OF THE OXIDATION OF STRUCTURAL IRON IN BIOTITE MICA BY SOLUTIONS CONTAINING BR-2 OR H2O2

XAFS measurements have been made on the Fe edge for a series of biotit e micas oxidized to different extents by solutions containing either B r-2 or H2O2. The Fe in the Br-2-treated sample is nearly completely ox idized to Fe(III), while the H2O2-treated samples showed an intermedia te degree of oxidization. Both the near-edge and EXAFS for the H2O2 sa mples could be fit well by a linear combination of the untreated and B r-2-treated samples. This indicates that the partially oxidized sample s have the two forms of Fe in distinct sites. Detailed analysis gave f or the oxidized site a coordination of 5.7 +/- 0.5 with a Fe-O distanc e of 1.99 Angstrom.