The Role of Dehydration in the Development of Laterite

SOIL FORMATION in tropical regions is determined by the nature and extent of the chemical weathering of the soil-formin g materials . The intense chemical weathering and the varying length of time of exposure of minerals to weathering have resulted in the development of a broad sequence of soil formation in the tropical areas of the world . Sherman (1949) has shown that the soils of the Hawaiian Islands "exhibit a sequence of soil development which can be related to a sequence of mine ral weathering as proposed byJackson et al. (1948). This sequence of soil formation represents a series of successive stages of secondary mineral development with the following order of soils rich in : (1) primary minerals; (2) montmorillonite; (3) kaolinite; (4) hydrated sesquioxides ; and (5) dehydrated sesquio xides. The end product of this weathering cycle would be either a ferruginous laterite or a bauxite laterite , depending on the environmental conditions . These two products represent two extremes of a wide range of weathered end-products, as the intermediate member a ferruginous bauxitic laterite-is quite common (Harrison, 1934). Ferruginous laterite was described by Buchanan (1807). As described by Buchanan, laterite is a soil horizon which has a very high content of iron oxides . These iron oxides exist as the minerals , limonite, goethite, hema-