Laterite
Laterite is a soil type rich in iron and aluminium and is commonly considered to have formed in hot and wet tropical areas.
They develop by intensive and prolonged weathering of the underlying parent rock, usually when there are conditions of high temperatures and heavy rainfall with alternate wet and dry periods.
After 1000 CE, construction at Angkor Wat and other southeast Asian sites changed to rectangular temple enclosures made of laterite, brick, and stone.
Locally available laterites have been used in an acid solution, followed by precipitation to remove phosphorus and heavy metals at sewage-treatment facilities.
[4]: 65 He named it laterite from the Latin word later, which means a brick; this highly compacted and cemented soil can easily be cut into brick-shaped blocks for building.
The mechanism of leaching involves acid dissolving the host mineral lattice, followed by hydrolysis and precipitation of insoluble oxides and sulfates of iron, aluminum and silica under the high temperature conditions[13] of a humid sub-tropical monsoon climate.
[15] Laterite formation is favored in low topographical reliefs of gentle crests and plateaus which prevents erosion of the surface cover.
[10]: 4 The reaction zone where rocks are in contact with water—from the lowest to highest water table levels—is progressively depleted of the easily leached ions of sodium, potassium, calcium and magnesium.
[6]: 6 Laterites consist mainly of quartz, zircon, and oxides of titanium, iron, tin, aluminum and manganese, which remain during the course of weathering.
[15] Nickel laterites occur in zones of the earth which experienced prolonged tropical weathering of ultramafic rocks containing the ferro-magnesian minerals olivine, pyroxene, and amphibole.
[6]: 2 Some of the oldest and most highly deformed ultramafic rocks which underwent laterization are found as petrified fossil soils in the complex Precambrian shields in Brazil and Australia.
[10]: 3 Smaller highly deformed Alpine-type intrusives have formed laterite profiles in Guatemala, Colombia, Central Europe, India and Burma.
[10]: 3 Large thrust sheets of Mesozoic island arcs and continental collision zones underwent laterization in New Caledonia, Cuba, Indonesian and the Philippines.
However, if the structure of lateritic soils becomes degraded, a hard crust can form on the surface, which hinders water infiltration, the emergence of seedlings, and leads to increased runoff.
The International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) has employed this system to rehabilitate degraded laterite soils in Niger and increase smallholder farmers' incomes.
[19] Upon exposure to air it gradually hardens as the moisture between the flat clay particles evaporates and the larger iron salts[15] lock into a rigid lattice structure[19]: 158 and become resistant to atmospheric conditions.
[1] After 1000 CE Angkorian construction changed from circular or irregular earthen walls to rectangular temple enclosures of laterite, brick and stone structures.
[24] It is used as a local building material in places such as Burkina Faso, where it is valued for being strong and for reducing heating and cooling costs.
[26] Kenya, during the mid-1970s, and Malawi, during the mid-1980s, constructed trial sections of bituminous-surfaced low-volume roads using laterite in place of stone as a base course.
[27] The laterite did not conform with any accepted specifications but performed equally well when compared with adjoining sections of road using stone or other stabilized material as a base.
[29]: 13 In some high-density suburban areas the water table could recede to 15 m (50 ft) below ground level during a prolonged dry period of more than 65 days.
[30] Locally available laterite—a low-grade bauxite rich in iron and aluminum—is used in acid solution, followed by precipitation to remove phosphorus and heavy metals at several sewage treatment facilities.
[30] A study, using both laboratory tests and pilot-scale constructed wetlands, reports the effectiveness of granular laterite in removing phosphorus and heavy metals from landfill leachate.
[30] There is a possible application of this low-cost, low-technology, visually unobtrusive, efficient system for rural areas with dispersed point sources of pollution.
[31] The remaining weight consists of silicas (quartz, chalcedony and kaolinite), carbonates (calcite, magnesite and dolomite), titanium dioxide and water.
[32] The bauxites form elongate belts, sometimes hundreds of kilometers long, parallel to Lower Tertiary shorelines in India and South America; their distribution is not related to a particular mineralogical composition of the parent rock.
[14] Primary olivine, plagioclase feldspar and augite were successively broken down and replaced by a mineral assemblage consisting of hematite, gibbsite, goethite, anatase, halloysite and kaolinite.
