LATERITE

Laterite, soil layer that is rich in iron oxide and derived from a wide variety of rocks weathering under strongly oxidizing and leaching conditions. It forms in tropical and subtropical regions where the climate is humid. Lateritic soils may contain clay minerals; but they tend to be silica-poor, for silica is leached out by waters passing through the soil. Typical laterite is porous and claylike. It contains the iron oxide minerals goethite, HFeO2; lepidocrocite, FeO(OH); and hematite, Fe2O3. It also contains titanium oxides and hydrated oxides of aluminum, the most common and abundant of which is gibbsite, Al2O3ยท3H2O. The aluminum-rich representative of laterite is bauxite.

Laterite is a residual material. This is what is left of common silicate rocks if we remove much of silica, alkali, and alkaline earth metals. It is mostly composed of iron, aluminum, titanium, and manganese oxides because these are the least soluble components of the rocks undergoing a type of chemical weathering known as laterization or lateritization. Iron-rich variety consists of hematite and goethite. These minerals give reddish color to the soil/rock and sometimes such deposits are mined for their iron and nickel content (in Cuba and New Caledonia). Aluminous laterite (bauxite) is mostly composed of aluminum hydroxides gibbsite, diaspore, and boehmite. Not all bauxites are laterites, though. Some bauxite deposits are associated with limestone and karst phenomena. Lateritic bauxite is a weathering product of aluminous silicate rocks (granite and similar). Laterite has been used as an iron ore and, in Cuba, as a source of nickel.