Evaluation of ferrolysis in soil formation


E. Van Ranst. E-mail: eric.vanranst@rug.ac.be


The concept of ferrolysis as defined in the 1970s by Brinkman and co-workers is mentioned in the recent literature as a dominant process to explain clay disintegration, interlayering of clay minerals, and strong texture contrast of duplex soils, in which bleaching and mottling are predominant features. Ferrolysis is based on biochemical reduction of free iron(III) oxides to Fe2+ and re-oxidation of Fe2+ during alternating reducing and oxidizing conditions in the soil. The acidity produced during the oxidation is assumed to release cations from silicates which results in the destruction of clay minerals.

 A detailed analysis of data from chemical analyses, laboratory experiments, and mineralogical and micromorphological investigations, which have been considered to sustain the ferrolysis theory, has been carried out. Some soils in Belgium and France, which have been considered to be formed mainly by ferrolysis, show strong textural contrast or albeluvic features. It has been shown that the development of these soils is due to clay translocation rather than to clay destruction by ferrolysis. Fine quartz and chlorite, assumed to be secondary minerals formed during ferrolysis, are more likely formed by disintegration of larger quartz and chlorite particles.