ABSTRACT
De-andosolization ƒ De-andosolization corresponds to the partial mineralization of organic matter. According to Sedov et al. (2003) clay appears through relative concentration (2/1 clay mineral) or through precipitation (halloysite or kaolinite). The structure becomes coarse polyhedral. Iron is released giving brown colour and sometimes oxidation-reduction mottles (redoximorphic features). In some cases the clay can migrate as indicated by localized coatings visible under the microscope. The soils progress to Cambisols and sometimes to Luvisols. When the Andosol is thick, the deeper horizons are largely removed from the influence of organic matter and drainage is less. Amorphous materials provided by weathering are often very visible there. These are yellow isotropic substances coating the coarse elements and filling up the voids. They are easily transformed to halloysite (Parfitt and Wilson 1985; Quantin 1992; Dubroeucq et al. 1998).
