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Magnetic fractionation, chemical, and structural analyses prove that alteration of ilmenite from Manavalakurichi deposit extends only up to the formation of pseudorutile with traces of rutile. The data indicate that ferrous to ferric iron transformation, ferric iron oxide formation, and iron removal contribute to the alteration sequence. The first two highly magnetic fractions are not unaltered ilmenite. A reduction in ilmenite unit cell volume indicates the ferrous-ferric conversion occurred during alteration.

It was a great honor for me to introduce Professor Joseph W. Stucki from the Department of Natural Resources and Environmental Sciences at the University of Illinois at Urbana-Champaign, the 2009 Recipient of The Marilyn and Sturges W. Bailey Distinguished Member Award, recognizing his excellent scientific achievements in pioneering systematic research on reduction and re-oxidation of ferric iron in the structure of clay minerals. Joe received his B.S. in Chemistry from Brigham Young University, Provo, Utah, in 1970, and M.S. in Soil Chemistry from Utah State University, Logan, Utah, in 1972. The next step in his career was the work on his PhD thesis Chemical and Spectroscopic Analysis of Oxidation-Reduction Mechanisms for Structural Iron in Nontronite at Purdue University, West Lafayette, Indiana. The results were discussed continuously not only with his advisor, Dr. Charles B. Roth, but also with two of his other committee members, who later became recipients of the CMS Distinguished Member Award, namely, Joe L. White (1990) and Philip F. Low (1992). The thesis was defended in 1975 resulting in Joe’s PhD degree in Soil Physical Chemistry, and, due to his scientific vision, it opened the door to his life-long research area of Fe(III) reduction and re-oxidation, mainly in Fe-rich smectites. It has continued and fully developed in Turner Hall at the University of Illinois at Urbana-Champaign, where Dr. Stucki was successively Assistant, Associate, and Full Professor of Soil Physical Chemistry from 1976 till his retirement …

Mossbauer spectra of 15 smectites were investigated. In these samples, ferric iron occupies both M(1) and M(2) octahedral sites, the distribution being partly determined by the relative covalency of the bonds formed. The quadrupole splittings are linearly related to b−3. They show that Fe3+ octahedra are much more distorted in montmorillonite and beidellite than in nontronite and volkonskoite and that M(1) sites are more prone to change than M(2). Ferrous iron occurs in relatively undistorted octahedra in some otherwise distorted octahedral sheets and vice versa.

Deferration by reduction of free Fe2O3 with Na2S2O4 in the presence of Na citrate and NaHCO3 caused a change in valence state of 10 to 35 per cent of the total structural iron in micaceous vermiculites, soils, nontronite, and muscovite. An increase in Fe2+ on deferration was accompanied by an equivalent decrease in Fe3+. Subsequent treatment with H2O2 reoxidized the structural Fe2+ previously formed. Sesquioxide coatings on micaceous vermiculites were examined electron microscopically. These coatings were composed predominantly of Fe2O3 with approximately 10 per cent by weight of Al2O3 and small amounts of SiO2, as determined by chemical analysis of the deferration extracts. The cation exchange capacity (CEC) increased 10–60 per cent as a result of deferration of micaceous vermiculites and soils. Treatment of the deferrated sample with H2O2 restored the Fe3+ content to approximately the original value but the CEC was not affected. Consequently, the increase in CEC on deferration was attributed to the removal of the positively charged sesquioxide coating. The reversible change in valence of structural iron without an equivalent change in CEC was attributed to deprotonation-protonation of the structure (OH− ⇄ O2−) simultaneous with the oxidation-reduction of iron (Fe2+ ⇄ Fe3+) in the phyllosilicate layer.

Oxidation of octahedral ferrous iron in biotite by saturated bromine water results in a loss of both octahedral and interlayer cations. The hydroxyl adjacent to vacant octahedral cation sites adopt an inclined orientation resulting in a more stable environment for interlayer cations. The only structural change accompanying these processes is a decrease in b-axis dimension which is linearly related to octahedral ferric iron content. These findings are in agreement with observations made on naturally weathered biotites.

It has been demonstrated that ferric iron is the principal source of the oxidizing action of the surface of attapulgite clay. The extent of oxidizing action in a given time (the oxidizing power) has been determined as a function of the temperature of calcination of the clay in the range 100–900°C. The oxidizing power was measured with TiCl3 in aqueous acid medium by direct titration of the clay in situ and by titration of extracts of the clay. The dissolution of the metallic cations of the clay was also studied in the same medium. The results have been correlated with structural changes caused by the calcination of attapulgite.

Artificial weathering of biotites, which contain various levels of structural ferric iron, by NaCI and NaBPh4 solutions produces minerals and structures similar to those described for naturally weathered biotites. Oxidation of structural iron leads to K removal from alternate layers and develop- ment of hydrobiotite. The growth of order with increasing ferric iron content has been assessed by comparison with theoretical calculations for random and most ordered interstratified structures. There is evidence for the existence of two layer types in biotite prior to oxidation. The depression in rates of K release due to oxidation has been confirmed.

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