Some bauxite deposits are associated with limestones and karst phenomena. These minerals give reddish color to the soil/rock and sometimes such deposits are mined for their iron and nickel content (in Cuba and New Caledonia).Īluminous laterite (bauxite) is mostly composed of aluminum hydroxides gibbsite, diaspore, and boehmite. Iron-rich laterite consists of hematite and goethite. It is mostly composed of iron, aluminum, titanium, and manganese oxides because these are the least soluble components of the rocks undergoing a type of chemical weathering known as laterization or lateritization. Iron-rich laterite is mostly used as a construction stone, especially in Asia. Some lateritic rocks (bauxite) are mined because of their high content. At least this is what it is in India where this rock or a soil type was first defined by a Scottish scientist Francis Buchanan-Hamilton in 1807.However, not all laterites are enriched in iron and sometimes they are not even reddish. Lateriteis a reddish weathering product of basalt. Pisolitic limestone Itaboraí, Rio de Janeiro, Brazil pisolith diameters average 1.0 cm. Jurassic Arab sequence in the Middle East Smackover reservoir of the Gulf of Mexico, and several formations in the Anadarko and Appalachian basins among others are examples of oil reservoirs in oolitic limestones. Oolitic limestones form prolific oil reservoirs. Ooids occurring in Ordovician limestone in Estonia are strikingly similar in chemical composition, internal structures and REE (rare earth elements) distribution to modern iron-bearing ooids described from a vicinity of volcanically active island in Indonesia. Oolite consisting of goethite (limonite) ooids from Germany Such ooids may form oolites which contain nothing but brown iron-rich ooids but more commonly they occur within other sedimentary rocks. Concentric layering in iron-bearing ooids is thought to result from constant agitation of ooids associated with currents and expulsion of gas from the sediment. Iron-bearing goethitic (limonitic) ooids are probably formed out of volcanic pyroclastic (volcanic ash) material deposited in sea. Especially phosphatic and iron-bearing ooids composed of hematite and goethite seem to have been formed as such. Such ooids are formed by replacement of original calcium carbonate but they may be also primary. Some ooids are made of silica (chert), dolomite or fine-grained phosphatic material (collophane). Ooid sand from Antelope Island, The Great Salt Lake Sometimes ooids form even in human-constructed features such as drainage pipes and Water treatment plant. Even ooids made of evaporite minerals gypsum and halite have been reported. Some ooids form in fresh-water lakes, caves, caliche soils, hot springs, and rivers. Some ooids form in non-marine environments, the Great salt Lake is probably the best known example of ooid formation in saline lake. Most modern ooids are composed of mineral aragonite. However, the exact formation mechanisms are still unresolved. It is believed that ooid formation is generally abiogenic process. Warm water is needed to lower the carbon dioxide content in water (higher temperature reduces the ability of water to keep gases dissolved) and thereby enhance the precipitation of calcium carbonate. This is also the reason why ooids are so well-polished. Ooids are kept moving by waves which enables accretion to occur on all sides. Ooids in these places form a distinct type of sand - ooid sand.