Laterite
Introduction
Laterite is a soil and rock type rich in iron and aluminium and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of high iron oxide content. They develop by intensive and prolonged weathering of the underlying parent rock. Tropical weathering (laterization) is a prolonged process of chemical weathering which produces a wide variety in the thickness, grade, chemistry and ore mineralogy of the resulting soils. The majority of the land area containing laterites is between the tropics of Cancer and Capricorn.
Formation and Characteristics
Laterite is characterized by a rich concentration of iron and aluminium oxides. It is formed through the process of weathering, which involves the disintegration of rocks and minerals at or near the Earth's surface through physical and chemical processes. In the case of laterite, weathering is particularly intense due to the hot, wet conditions found in tropical regions. This leads to the leaching of silica and other soluble materials, leaving behind a concentration of iron and aluminium oxides and hydroxides. This process is known as laterization.
Laterite soils are generally poor in nutrients due to the high rate of leaching, which washes away soluble nutrients. However, they can be agriculturally productive with the right management and when the water table is high enough, the iron and aluminium oxides can form hard layers known as ironstone and aluminous duricrusts.
Classification
Laterites can be classified on the basis of the dominant ore mineral. When iron is dominant, the term 'ferralite' is often used, while 'bauxite' is used when aluminium is dominant. Ferralites are characterized by the presence of goethite and hematite, while bauxites are characterized by the presence of gibbsite, boehmite, and diaspore.
Distribution and Use
Laterite covers are thick in the stable areas of the Western Ethiopian Shield, on cratons of the South American Plate, and on the Australian Shield. In Madhya Pradesh, India, the laterite which caps the plateau is 30 m (100 ft) thick. Laterites can be either soft and easily broken into smaller pieces, or firm and physically resistant. Church towers built of local laterites in the region between Dharwad and Bijapur in the Indian state of Karnataka show a variety of structural and ornamental soundness that depends on the proportion of clay in the local laterite bricks.
Laterite is both a soil and a rock type rich in iron and aluminium, and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of high iron oxide content. They develop by intensive and prolonged weathering of the underlying parent rock. Tropical weathering (laterization) is a prolonged process of chemical weathering which produces a wide variety in the thickness, grade, chemistry and ore mineralogy of the resulting soils. The majority of the land area containing laterites is between the tropics of Cancer and Capricorn.
Economic Importance
Laterite soils have a high potential for aluminium and iron extraction. They are a major source of aluminium ore and are also used in the production of nickel. Bauxite, a type of laterite, is the primary ore used in the production of aluminium.
In addition to their industrial uses, laterites are used in construction. In regions where they are common, laterites are often used in the manufacture of bricks for building construction. The high iron content gives the bricks a distinctive red color and hardness, making them suitable for use in construction.
Environmental Impact
The mining of laterite can have significant environmental impacts. The removal of the top layer of soil in order to access the ores beneath can lead to deforestation, soil erosion, and a loss of biodiversity. Additionally, the process of extracting the metals from the ores can result in the release of harmful substances into the environment.