Soils - a unique environment for iron oxide formation in terrestrial ecosystems

Soils - a unique environment for iron oxide formation in terrestrial ecosystems 

Almost all rocks contain at least some iron. The more important minerals, in which Fe is a major constituent, are given with their Fe contents in Table 16.1. In all of these minerals except magnetite, iron is exclusively or predominantly in the bivalent state. During weathering, the iron is released from these minerals and secondary , pedogenic iron minerals are formed. The most important ones are Fe-contain-ing clay silicates and Fe oxides but under reducing conditions, Fe carbonates, sulphides and phosphates may also be formed. 

The Iron Oxides Structure, Properties, Reactions, Occurences and Uses. R. M. Cornell, U. Schwertmann Copyright 2003 WILEY-VCH Verlag GmbH Co. KGaA.Weinheim ISBN 3-527-30274-3 

The physical and chemical parameters which influence iron oxide formation vary with time and space, e. g. through changing water/air content. Microenvironments exist in pores of different sizes and with different degrees of filling. For example, hematite was identified in coatings at the (dry) surface of a basalt boulder, whereas goethite occurred in a nearby (moister) crack (Bender-Koch et al., 1995 a). In another case, goethite was the dominant oxide next to the root surface, whereas lepidocrocite predominated a few mm away from it (Schwertmann Fitzpatrick, 1977). Often, however, the exact conditions under which Fe oxides form are difficult to determine. 

In conclusion, the pedosphere is an environment of active mineral formation and transformation and exhibits a large variation in formation parameters in space and time over a range of scales. It openly and permanently communicates with neigh- 

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