LATERITE

Laterite is a 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, Al₂O₃·3H₂O. The aluminum-rich representative of laterite is bauxite.

Laterite is frequently pisolitic (pealike). Exposed surfaces are blackish-brown to reddish and commonly have a slaggy, or scoriaceous, lavalike appearance. Commonly lighter in color (red, yellow, and brown) when freshly broken, it is generally soft when freshly quarried but hardens on exposure.