1.
Laterite
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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 iron oxide content. They develop by intensive and long-lasting weathering of the parent rock. Tropical weathering is a process of chemical weathering which produces a wide variety in the thickness, grade, chemistry. The majority of the area containing laterites is between the tropics of Cancer and Capricorn. Laterite has commonly referred to as a soil type as well as being a rock type. This and further variation in the modes of conceptualizing about laterite has led to calls for the term to be abandoned altogether, at least a few researchers specializing in regolith development have considered that hopeless confusion has evolved around the name. Historically, laterite was cut into shapes and used in monument-building. After 1000 CE, construction at Angkor Wat and other southeast Asian sites changed to rectangular temple enclosures made of laterite, brick, since the mid-1970s, some trial sections of bituminous-surfaced, low-volume roads have used laterite in place of stone as a base course. Thick laterite layers are porous and slightly permeable, so the layers can function as aquifers in rural areas, locally available laterites have been used in an acid solution, followed by precipitation to remove phosphorus and heavy metals at sewage-treatment facilities. Laterites are a source of ore, the ore exists largely in clay minerals and the hydroxides, gibbsite, boehmite, and diaspore. In Northern Ireland they once provided a source of iron. Laterite ores also were the major source of nickel. Francis Buchanan-Hamilton first described and named a laterite formation in southern India in 1807 and 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 word laterite has been used for variably cemented, sesquioxide-rich soil horizons, a sesquioxide is an oxide with three atoms of oxygen and two metal atoms. It has also used for any reddish soil at or near the Earths surface. Laterite covers are thick in the areas of the Western Ethiopian Shield, on cratons of the South American Plate. In Madhya Pradesh, India, the laterite which caps the plateau is 30 m thick, laterites can be either soft and easily broken into smaller pieces, or firm and physically resistant
2.
Regolith
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Regolith is a layer of loose, heterogeneous superficial material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, Mars, some asteroids, the term regolith combines two Greek words, rhegos, blanket, and lithos, rock. Merrill first defined the term in 1897, writing, In places this covering is made up of material originating through rock-weathering or plant growth in situ, in other instances it is of fragmental and more or less decomposed matter drifted by wind, water or ice from other sources. This entire mantle of unconsolidated material, whatever its nature or origin, biota and organic components derived from it. Regolith can vary from being essentially absent to hundreds of metres in thickness and its age can vary from instantaneous to hundreds of millions of years old. Regolith on Earth originates from weathering and biological processes, if it contains a significant proportion of biological compounds it is conventionally referred to as soil. People also call various types of earthly regolith by such names as dirt, dust, gravel, sand, Regolith is also important to engineers constructing buildings, roads and other civil works. The mechanical properties of regolith vary considerably and need to be documented if the construction is to withstand the rigors of use, Regolith may host many mineral deposits, for example mineral sands, calcrete uranium, and lateritic nickel deposits, among others. Elsewhere, understanding regolith properties, especially geochemical composition, is critical to geochemical and geophysical exploration for mineral deposits beneath it, the regolith is also an important source of construction material, including sand, gravel, crushed stone, lime, and gypsum. The regolith is the zone through which aquifers are recharged and through which aquifer discharge occurs, many aquifers, such as alluvial aquifers, occur entirely within regolith. The composition of the regolith can also strongly influence water composition through the presence of salts, Regolith covers almost the entire lunar surface, bedrock protruding only on very steep-sided crater walls and the occasional lava channel. The impact of micrometeoroids, sometimes travelling faster than 96,000 km/h and this melting and refreezing welds particles together into glassy, jagged-edged agglutinates, reminiscent of tektites found on Earth. The regolith is generally from 4 to 5 m thick in mare areas, below this true regolith is a region of blocky and fractured bedrock created by larger impacts, which is often referred to as the megaregolith. The density of regolith at the Apollo 15 landing site averages approximately 1.35 g/cm3 for the top 30 cm, and it is approximately 1. 85g/cm3 at a depth of 60 cm. The term lunar soil is used interchangeably with lunar regolith but typically refers to the finer fraction of regolith. Some have argued that the soil is not correct in reference to the Moon because soil is defined as having organic content. However, standard usage among lunar scientists is to ignore that distinction, lunar dust generally connotes even finer materials than lunar soil, the fraction which is less than 30 micrometers in diameter. The average chemical composition of regolith might be estimated from the concentration of elements in lunar soil
3.
Weathering
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Weathering is the breaking down of rocks, soil, and minerals as well as wood and artificial materials through contact with the Earths atmosphere, waters, and biological organisms. Two important classifications of weathering processes exist – physical and chemical weathering, mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure. While physical weathering is accentuated in very cold or very dry environments, chemical reactions are most intense where the climate is wet, however, both types of weathering occur together, and each tends to accelerate the other. For example, physical abrasion decreases the size of particles and therefore increases their surface area, the various agents act in concert to convert primary minerals to secondary minerals and release plant nutrient elements in soluble forms. The materials left over after the rock breaks down combined with organic material creates soil, in addition, many of Earths landforms and landscapes are the result of weathering processes combined with erosion and re-deposition. Physical weathering, also recognized as mechanical weathering, is the class of processes that causes the disintegration of rocks without chemical change, the primary process in physical weathering is abrasion. However, chemical and physical weathering often go hand in hand, physical weathering can occur due to temperature, pressure, frost etc. For example, cracks exploited by physical weathering will increase the area exposed to chemical action. Abrasion by water, ice, and wind loaded with sediment can have tremendous cutting power, as is amply demonstrated by the gorges, ravines. In glacial areas, huge moving ice masses embedded with soil and rock fragments grind down rocks in their path, plant roots sometimes enter cracks in rocks and pry them apart, resulting in some disintegration, Burrowing animals may help disintegrate rock through their physical action. However, such influences are usually of importance in producing parent material when compared to the drastic physical effects of water, ice, wind. Physical weathering is called mechanical weathering or disaggregation. Thermal stress weathering results from the expansion and contraction of rock, for example, heating of rocks by sunlight or fires can cause expansion of their constituent minerals. As some minerals expand more than others, temperature changes set up differential stresses that cause the rock to crack apart. Because the outer surface of a rock is often warmer or colder than the more protected inner portions and this process may be sharply accelerated if ice forms in the surface cracks. When water freezes, it expands with a force of about 1465 Mg/m^2, disintegrating huge rock masses, thermal stress weathering comprises two main types, thermal shock and thermal fatigue. Thermal stress weathering is an important mechanism in deserts, where there is a diurnal temperature range, hot in the day. The repeated heating and cooling exerts stress on the layers of rocks
4.
Groundwater
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Groundwater is the water present beneath Earths surface in soil pore spaces and in the fractures of rock formations. A unit of rock or a deposit is called an aquifer when it can yield a usable quantity of water. The depth at which pore spaces or fractures and voids in rock become completely saturated with water is called the water table. Groundwater is recharged from, and eventually flows to, the naturally, natural discharge often occurs at springs and seeps. Groundwater is also withdrawn for agricultural, municipal, and industrial use by constructing and operating extraction wells. The study of the distribution and movement of groundwater is hydrogeology, Groundwater is hypothesized to provide lubrication that can possibly influence the movement of faults. It is likely that much of Earths subsurface contains some water, Groundwater may not be confined only to Earth. The formation of some of the landforms observed on Mars may have influenced by groundwater. There is also evidence that water may also exist in the subsurface of Jupiters moon Europa. Groundwater is often cheaper, more convenient and less vulnerable to pollution than surface water, therefore, it is commonly used for public water supplies. For example, groundwater provides the largest source of water storage in the United States. Underground reservoirs contain far more water than the capacity of all surface reservoirs and lakes in the US, many municipal water supplies are derived solely from groundwater. Polluted groundwater is less visible, but more difficult to clean up, than pollution in rivers, Groundwater pollution most often results from improper disposal of wastes on land. An aquifer is a layer of substrate that contains and transmits groundwater. When water can flow directly between the surface and the zone of an aquifer, the aquifer is unconfined. The deeper parts of unconfined aquifers are more saturated since gravity causes water to flow downward. The upper level of this layer of an unconfined aquifer is called the water table or phreatic surface. Below the water table, where in general all pore spaces are saturated with water, is the phreatic zone, substrate with low porosity that permits limited transmission of groundwater is known as an aquitard
5.
Bauxite
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Bauxite, an aluminium ore, is the worlds main source of aluminium. It consists mostly of the minerals gibbsite, boehmite and diaspore, mixed with the two iron oxides goethite and haematite, the mineral kaolinite and small amounts of anatase. In 1821 the French geologist Pierre Berthier discovered bauxite near the village of Les Baux in Provence, in 1861, French chemist Henri Sainte-Claire Deville named the mineral bauxite. Lateritic bauxites are distinguished from karst bauxite ores, the lateritic bauxites are found mostly in the countries of the tropics. They were formed by lateritization of various silicate rocks such as granite, gneiss, basalt, syenite, in comparison with the iron-rich laterites, the formation of bauxites depends even more on intense weathering conditions in a location with very good drainage. This enables the dissolution of the kaolinite and the precipitation of the gibbsite, zones with highest aluminium content are frequently located below a ferruginous surface layer. The aluminium hydroxide in the bauxite deposits is almost exclusively gibbsite. In 2009, Australia was the top producer of bauxite with almost one-third of the production, followed by China, Brazil, India. Although aluminium demand is increasing, known reserves of its bauxite ore are sufficient to meet the worldwide demands for aluminium for many centuries. Increased aluminium recycling, which has the advantage of lowering the cost in power in producing aluminium. In November 2010, Nguyen Tan Dung, the minister of Vietnam, announced that Vietnams bauxite reserves might total 11000 Mt. Bauxite is usually strip mined because it is almost always found near the surface of the terrain, as of 2010, approximately 70% to 80% of the worlds dry bauxite production is processed first into alumina and then into aluminium by electrolysis. Bauxite rocks are classified according to their intended commercial application, metallurgical, abrasive, cement, chemical. Usually, bauxite ore is heated in a vessel along with a sodium hydroxide solution at a temperature of 150 to 200 °C. At these temperatures, the aluminium is dissolved as sodium aluminate, the aluminium compounds in the bauxite may be present as gibbsite, boehmite or diaspore, the different forms of the aluminium component will dictate the extraction conditions. The undissolved waste, bauxite tailings, after the aluminium compounds are extracted contains iron oxides, silica, calcia, titania, after separation of the residue by filtering, pure gibbsite is precipitated when the liquid is cooled, and then seeded with fine-grained aluminium hydroxide. The gibbsite is usually converted into aluminium oxide, Al2O3, by heating in rotary kilns or fluid flash calciners to a temperature in excess of 1000oC and this aluminium oxide is dissolved at a temperature of about 960 °C in molten cryolite. Prior to the invention of this process in 1886, elemental aluminium was made by heating ore along with sodium or potassium in a vacuum
6.
Gold
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Gold is a chemical element with symbol Au and atomic number 79. In its purest form, it is a bright, slightly yellow, dense, soft, malleable. Chemically, gold is a metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions, Gold often occurs in free elemental form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the element silver and also naturally alloyed with copper. Less commonly, it occurs in minerals as gold compounds, often with tellurium, golds atomic number of 79 makes it one of the higher numbered, naturally occurring elements. It is thought to have produced in supernova nucleosynthesis, from the collision of neutron stars. Because the Earth was molten when it was formed, almost all of the present in the early Earth probably sank into the planetary core. Gold is resistant to most acids, though it does dissolve in aqua regia, a mixture of acid and hydrochloric acid. Gold also dissolves in solutions of cyanide, which are used in mining and electroplating. Gold dissolves in mercury, forming amalgam alloys, but this is not a chemical reaction, as a precious metal, gold has been used for coinage, jewelry, and other arts throughout recorded history. A total of 186,700 tonnes of gold is in existence above ground, the world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry. Gold is also used in infrared shielding, colored-glass production, gold leafing, certain gold salts are still used as anti-inflammatories in medicine. As of 2014, the worlds largest gold producer by far was China with 450 tonnes, Gold is cognate with similar words in many Germanic languages, deriving via Proto-Germanic *gulþą from Proto-Indo-European *ǵʰelh₃-. The symbol Au is from the Latin, aurum, the Latin word for gold, the Proto-Indo-European ancestor of aurum was *h₂é-h₂us-o-, meaning glow. This word is derived from the root as *h₂éu̯sōs, the ancestor of the Latin word Aurora. This etymological relationship is presumably behind the frequent claim in scientific publications that aurum meant shining dawn, Gold is the most malleable of all metals, a single gram can be beaten into a sheet of 1 square meter, and an avoirdupois ounce into 300 square feet. Gold leaf can be thin enough to become semi-transparent
