Isomorphous Substitution of Iron for Aluminium in some Soil Kaolinites

P. Rengasamy, G. S. R. Krishna Murti and V. A. K. Sarma
Indian Agricultural Research Institute, New Delhi 110 012, India
* Complete description of the soil profiles was reported by Rengasamy (1973).

Abstract: Clay (<2 µm) and fine silt (2–20 µm) fractions of twenty seven soil samples from eight tropical ferruginous profiles of the Mysore Plateau (India) were analysed for kaolinite by dehydroxylation and selective dissolution. The considerable amounts of iron extracted by the procedure and the closeness of the SiO2/R2O3 molar ratios (2·00–2·18) to the ideal value of 2·00 indicated that iron was a structural constituent of the kaolinites. The calculated unit cell cation composition of the kaolinites showed a substitution of 0·11–0·82 atoms of Fe(III) for Al in every four octahedral sites. The kaolinites in these soils appear to be products of crystallization from weathering solutions.

Clays and Clay Minerals; July 1975 v. 23; no. 3; p. 211-214; DOI: 10.1346/CCMN.1975.0230308
© 1975, The Clay Minerals Society
Clay Minerals Society (www.clays.org)