MIXED-VALENCE OF IRON IN NATURAL VONSENITE

The exchange of electrons between adjacent ions in different oxidation states in vonsenite was observed using Mossbauer spectroscopy. The Mo ssbauer spectra of a series of naturally occurring vonsenite were reco rded over a temperature range of 120-773 K. Four quadrupole doublets w ere resolved by computer fitting and assigned to Fe2+(Fel), Fe2+(Fe3), Fe3+(Fe2, Fe4) and Fe2+-Fe3+(Fe2-Fe4). The percentage of iron sites p articipating in an electron exchange process increases from 17% betwee n 120 and 298 K to 27% between 573 and 773 K.