A Mössbauer and I.R. Spectroscopic Study of the Structure of Nontronite

Mössbauer and i.r. spectra of a series of nontronites show that Fe 3+ and Al 3+ are distributed between tetrahedral and octahedral sites. The Mössbauer results have reaffirmed the occupation by Fe 3+ of octahedral sites at which these ions are coordinated to pairs of OH groups in both cis and trans configurations. The distribution of Fe 3+ between these two sites varies considerably but in all of the nontronites some Fe 3+ occurs in the trans site in contrast to the all cis occupancy of the centro-symmetric structure proposed by Mering and Oberlin (1967). In one of the nontronites the distribution of Fe 3+ between these two sites approaches that in the ideal non-centrosymmetric structure proposed for montmorillonite.