Laterite

red ferruginous or ferruginous-aluminiferous eluvial formations typical of humid tropical and subtropical regions. The term “laterite” was first proposed by the English geologist F. Buchanan in 1807 to designate the red ferruginous rocks of the weathering mantle, used in India and other countries to make bricks used in construction. Later the term came to be used for a group of red rocks that differed in composition and origin. In soil science “laterite” is often used to denote ferruginous soil horizons of infiltrative origin. Climate is the chief factor in tropical weathering. Laterite forms only in tropical and subtropical regions with more than 1,300–2,000 mm of average annual precipitation and mean annual temperatures of 20°-30° C. The laterites overlie aluminosilicate rocks of various composition and form through laterization, during which up to 90 percent of the SiO₂ and bases (of their total content in the parent rock) are removed.

In the tropical zone of the globe laterites cover vast plateaus and hilly areas. Their thickness ranges from a few meters to 50 m. Their age varies from Jurassic to Recent.

In the USSR residual and redeposited laterites of Mesozoic and Cenozoic age are found in the Ukraine, Kazakhstan, Siberia, the Urals, and in Middle Asia. Abroad the development of laterite of Recent (Anthropogene) age has been proved in the Democratic Republic of Vietnam and on Pacific islands (Hawaii, Samoa, Tahiti).

Various minerals are associated with laterites, including aluminum, iron, manganese, nickel, and other ores (Cuba, New Caledonia) and very large bauxite deposits (Guinea, Ghana). In India laterite is used to make bricks used in construction.