laterites

Laterites are highly weathered rock materials formed under hot, humid tropical and subtropical climates. They are not a single rock type but a class of materials produced by intense chemical weathering, often occurring as crusts, soils, or partially consolidated rocks rich in iron and aluminum oxides.

Formation and composition: In regions with abundant rainfall and high temperatures, soluble elements such as silica, calcium, potassium, and sodium are leached from the parent rock. Iron and aluminum oxides accumulate in the residual horizon, and clay minerals such as kaolinite may form. The material can become cemented by ferric oxides, producing a dense, hard crust or pan. Common minerals include goethite and hematite (iron oxides) and gibbsite or boehmite (aluminum hydroxides). A typical laterite profile features a surface rind enriched in iron oxides over a softer, clay-rich subsurface; in some settings, the crust can harden into a durable layer.

Types and deposits: Two main types are ferruginous laterites (iron-rich) and aluminous laterites (aluminum-rich). Aluminous laterites can evolve into bauxite deposits under favorable conditions. Laterite soils in tropical climates are often poor in plant-available nutrients because of extensive leaching, though some forest ecosystems thrive on them.

Distribution and uses: Laterites are widespread in tropical regions, including Africa, South America, Southeast Asia, Australia, and India. They are valued as building material (red brick and paving blocks) and as road base in many regions. In agriculture, lateritic soils typically require amendment for cultivation due to low fertility and shallow depth.