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Laterite

Laterite is a soil type rich in iron and aluminum that often forms in hot, wet areas; most such soil is found in the tropics. Nearly all laterites are of rusty-red coloration due to high iron oxide content.

Laterite soils develop by intensive and prolonged weathering of the underlying parent rock, usually under conditions of high temperatures and heavy rainfall alternating with dry periods, in a process called laterization. Such prolonged chemical weathering produces a wide variety in the thickness, grade, chemistry and ore mineralogy of the resulting soils. Aside from this variety, laterite has commonly been considered a rock type as well as a soil type. These facts, and further ways of conceiving the nature of laterite (e.g. as a complete weathering profile or even a theory about weathering), have led to calls for the term to be abandoned altogether. At least a few researchers specializing in regolith development, including T. R. Paton and M. A. J. Williams, have suggested that hopeless confusion has evolved around the name. Material that looks much like Indian laterite occurs abundantly worldwide.

Historically, laterite was cut into brick-like shapes and used in monument-building. After 1000 AD, construction at Angkor Wat and other southeast Asian sites changed to rectangular temple enclosures made of laterite, brick, and stone. Since the mid-1970s, some trial sections of bituminous-surfaced, low-volume roads have used laterite in place of stone as a base course. Thick laterite layers are porous and slightly permeable, so the layers can function as aquifers in rural areas. Locally available laterites have also been used to treat sewage, for example in an acid solution followed by precipitation to remove phosphorus and heavy metals.

Laterites are a source of aluminum ore; the ore exists largely in clay minerals and the hydroxide minerals gibbsite, boehmite, and diaspore, and so resembles the composition of bauxite, the world's main source of aluminum ore. In Northern Ireland laterites once provided a major source of iron and aluminum ores. Laterite ores also were the early major source of nickel. Provided by Wikipedia