Laterite

Laterite (from Latin later " Brick " ) is a frequently encountered in tropical areas surface product that is produced by intensive and long lasting weathering of the underlying rocks. At the air -dried laterite used in some parts of the world as Bauziegel. A very similar rock but with lower iron / hematite content is referred to as bauxite, there is between the two rocks a continuous transition to possible chemical compositions.

Demarcation

In the geosciences only the mineralogical and chemical most altered weathering products are referred to as laterite; the less weathered, but often very similar looking and in the tropics and subtropics, the most widespread surface formations, however, as saprolite. Both weathering products can be classified as a residual or Residualgesteine ​​(see sedimentary rocks ).

Origin and composition

The rocks at the surface are decomposed deep under the influence of high temperatures and precipitation in the tropics, where the minerals occurring in the parent rocks are largely solved. This chemical weathering, a high proportion of readily soluble elements as sodium, potassium, calcium, magnesium and silicon ( silica) will be continued in percolating rainwater, making it a strong residue accumulation of less soluble elements iron and aluminum is ( Ferrallitisierung ).

Laterites exist alongside the derived from the parent rock, only slightly soluble quartz mainly from the newly formed minerals in the weathering of kaolinite, goethite, hematite and gibbsite ( gibbsite ). The iron oxides goethite and hematite cause the most red-brown color of laterites which are usually only a few meters thick, but may reach much higher thicknesses.

Laterites are either soft or crumbly or hard and physically robust; they can be cut in blocks from the ground and used as building blocks for simple houses. Famous historical examples are built from Lateritsteinen temples of Angkor. On this use and the Latin word later = Brick the term laterite is declining. Nowadays harder Late Rita parts, especially in the local road ( laterite ) are used. Also Lateritkies is often used in aquariums, where he is to influence the growth of tropical plants cheap.

Lateritic soils form the uppermost portion of the Lateritdecken; this are in soil science special names are in use ( Oxisol, Latosol etc.).

Occurrence

Laterites have developed over nearly all rock types in areas that do not have a strong relief, so that the weathering ceilings were preserved and not the erosion fell victim. Laterites in non-tropical climates today are a product of past geological epochs.

Deposits in laterites

The lateritization is particularly important for the formation of lateritic deposits. Bauxite is aluminum - rich Lateritvarietäten that can form from many rocks if the drainage is particularly intense. This causes a very strong removal of silicon and a correspondingly high concentration of aluminum in particular as gibbsite. The ultramafic rocks lateritization ( serpentinite, dunite, peridotite with 0.2-0.3 % Ni) can lead to significant nickel enrichment. Two types of lateritic nickel ores are distinguished: A very iron-rich Ni- limonite ore to the surface contains 1-2 % nickel bonded to goethite, which is highly enriched due to major solution of silicon and magnesium. Below this zone is in some deposits of nickel silicate ore with often more than 2% Ni, which is bound in silicates, especially serpentine. In addition, mostly excreted in pockets and fissures of Serpentinits green garnierite in small quantities, but with very high nickel contents of 20-40%. It is a mixture of different Ni- rich layer silicates. The total present in the silicate zone nickel was released from the overlying goethite zone and shifted Descendant. The absence of goethite zone is due to erosion.