The dregs of weathering: Secrets of kaolin and iron oxides in tropical soils
Robert J. Gilkes, School Earth & Geophysical Sciences, University of Western Australia, 35 Stirling Hwy, Crawley WA 6009, Australia, Fax: +61 (8) 9380 1050, bob.gilkes@uwa.edu.au, Phone: +61 (8) 9386 7374

Textbooks on soil science and regolith geology devote relatively few pages to the properties of the unglamorous products of extreme weathering: kaolin and iron oxides. However, these minerals present a diversity of crystal properties and compositions that helps explain variations in geochemistry and soil fertility in apparently quite uniform soils. Thus differences in kaolin crystal morphology can be used to trace the origins of complex polygenetic regolith materials, thereby aiding mineral exploration. Iron oxides can accommodate many metal substituents and an understanding of this process helps explain both the formation and exploitation of ore deposits. Climate change has left its imprint as fire and aridification have modified kaolin and goethite, which formed under previous wetter climates. These ubiquitous minerals of tropical soils conceal many other secrets that can be discovered by the micromineralogist using modern techniques.