Goethite and hematite in some solls from the amazon region

Abstract

Goethite and hematite in four soi!s from the Brazilian Amazon region were examined. Color of the clay fractions in these soi!s became redder and darker with increasing iron content. Aluminium was isomorphously substituted for less than 33% of iron in both geothite and hematite. Two types of goethite at least were noticed in the morphology and the dehydration pattern. One type showed hexagonal or square plates in the electron micrograph, and lost most of the structural water at a temperature near 370°C. Another was acicular in morphology, and most of the structural water was released near 300°C. The particles of hematite in the electron micrograph were very fine, about 5 to 8 nm in diameter, which was approximately one-tenth smaller than that reported in the other studies. Tbe phenomenon for soi! hematite to act as the cementing materials on the formation of stable microaggregates was also observed by the electron microscopy. © 1983 Taylor & Francis Group, LLC.