Kaolinite

Kaolinite (/ˈkeɪəlɪnaɪt/)[4][5] is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O5(OH)4. It is a layered silicate mineral, with one tetrahedral sheet of silica (SiO
4
) linked through oxygen atoms to one octahedral sheet of alumina (AlO
6
) octahedra.[6] Rocks that are rich in kaolinite are known as kaolin /ˈkeɪəlɪn/ or china clay.[7]

The name "kaolin" is derived from "Gaoling" (Chinese: 高嶺; pinyin: Gāolǐng; literally: 'High Ridge'), a Chinese village near Jingdezhen in southeastern China's Jiangxi Province.[8] The name entered English in 1727 from the French version of the word: kaolin, following François Xavier d'Entrecolles's reports on the making of Jingdezhen porcelain.[9]

Kaolinite has a low shrink–swell capacity and a low cation-exchange capacity (1–15 meq/100 g). It is a soft, earthy, usually white, mineral (dioctahedral phyllosilicate clay), produced by the chemical weathering of aluminium silicate minerals like feldspar. In many parts of the world it is colored pink-orange-red by iron oxide, giving it a distinct rust hue. Lighter concentrations yield white, yellow, or light orange colors. Alternating layers are sometimes found, as at Providence Canyon State Park in Georgia, United States. Commercial grades of kaolin are supplied and transported as dry powder, semi-dry noodle or as liquid slurry.

Kaolinite
Kaolinite from Twiggs County in Georgia in USA
General
CategoryPhyllosilicates
Kaolinite-serpentine group
Formula
(repeating unit)
Al
2
Si
2
O
5
(OH)
4
Strunz classification9.ED.05
Crystal systemTriclinic
Crystal classPedial (1)
(same H-M symbol)
Space groupP1
Unit cella = 5.13 Å, b = 8.89 Å
c = 7.25 Å; α = 90°
β = 104.5°, γ = 89.8°; Z = 2
Identification
ColorWhite, sometimes red, blue or brown tints from impurities
Crystal habitRarely as crystals, thin plates or stacked, More commonly as microscopic pseudohexagonal plates and clusters of plates, aggregated into compact, claylike masses
CleavagePerfect on {001}
TenacityFlexible but inelastic
Mohs scale hardness2–2.5
LusterPearly to dull earthy
StreakWhite
Specific gravity2.16–2.68
Optical propertiesBiaxial (–)
Refractive indexnα = 1.553–1.565,
nβ = 1.559–1.569,
nγ = 1.569–1.570
2V angleMeasured: 24° to 50°, Calculated: 44°
References[1][2][3]
Kaolinite
Traditional Chinese高嶺石
Simplified Chinese高岭石
Literal meaning"Gaoling stone"

Chemistry

Notation

The chemical formula for kaolinite as used in mineralogy is Al
2
Si
2
O
5
(OH)
4
,[3] however, in ceramics applications the formula is typically written in terms of oxides, thus the formula for kaolinite is Al
2
O
3
 · 2SiO
2
 · 2H2O.[10]

Beevers crystal structure model of Kaolinite
Kaolinite structure, showing the interlayer hydrogen bonds[11]

Structural transformations

Kaolinite group clays undergo a series of phase transformations upon thermal treatment in air at atmospheric pressure.

Drying

Below 100 °C (212 °F), exposure to dry air will slowly remove liquid water from the kaolin. The end-state for this transformation is referred to as "leather dry". Between 100 °C and about 550 °C (1,022 °F), any remaining liquid water is expelled from kaolinite. The end state for this transformation is referred to as "bone dry". Throughout this temperature range, the expulsion of water is reversible: if the kaolin is exposed to liquid water, it will be reabsorbed and disintegrate into its fine particulate form. Subsequent transformations are not reversible, and represent permanent chemical changes.

Metakaolin

Endothermic dehydration of kaolinite begins at 550–600 °C producing disordered metakaolin, but continuous hydroxyl loss is observed up to 900 °C (1,650 °F).[12] Although historically there was much disagreement concerning the nature of the metakaolin phase, extensive research has led to a general consensus that metakaolin is not a simple mixture of amorphous silica (SiO
2
) and alumina (Al
2
O
3
), but rather a complex amorphous structure that retains some longer-range order (but not strictly crystalline) due to stacking of its hexagonal layers.[12]

Spinel

Further heating to 925–950 °C converts metakaolin to an aluminium-silicon spinel which is sometimes also referred to as a gamma-alumina type structure:

Platelet mullite

Upon calcination above 1050 °C, the spinel phase nucleates and transforms to platelet mullite and highly crystalline cristobalite:

Needle mullite

Finally, at 1400 °C the "needle" form of mullite appears, offering substantial increases in structural strength and heat resistance. This is a structural but not chemical transformation. See stoneware for more information on this form.

Occurrence

Kaolinite is one of the most common minerals; it is mined, as kaolin, in Malaysia, Pakistan, Vietnam, Brazil, Bulgaria, Bangladesh, France, the United Kingdom, Iran, Germany, India, Australia, South Korea, the People's Republic of China, the Czech Republic, Spain, South Africa, and the United States.[1]

Mantles of kaolinitic saprolite are common in Western and Northern Europe. The ages of these mantles are Mesozoic to Early Cenozoic.[13]

Kaolinite clay occurs in abundance in soils that have formed from the chemical weathering of rocks in hot, moist climates—for example in tropical rainforest areas. Comparing soils along a gradient towards progressively cooler or drier climates, the proportion of kaolinite decreases, while the proportion of other clay minerals such as illite (in cooler climates) or smectite (in drier climates) increases. Such climatically-related differences in clay mineral content are often used to infer changes in climates in the geological past, where ancient soils have been buried and preserved.

In the Institut National pour l'Etude Agronomique au Congo Belge (INEAC) classification system, soils in which the clay fraction is predominantly kaolinite are called kaolisol (from kaolin and soil).[14]

In the US, the main kaolin deposits are found in central Georgia, on a stretch of the Atlantic Seaboard fall line between Augusta and Macon. This area of thirteen counties is called the "white gold" belt; the small town of Sandersville is known as the "Kaolin Capital of the World" due to its abundance of kaolin.[15][16] In the late 1800s, an active kaolin surface-mining industry existed in the extreme southeast corner of Pennsylvania, near the towns of Landenberg and Kaolin, and in what is present-day White Clay Creek Preserve. The product was brought by train to Newark, Delaware, on the Newark-Pomeroy line, along which can still be seen many open-pit clay mines. The deposits were formed between the late Cretaceous and early Paleogene, about 100 million to 45 million years ago, in sediments derived from weathered igneous and metakaolin rocks.[8] Kaolin production in the US during 2011 was 5.5 million tons.[17]

During the Paleocene–Eocene Thermal Maximum sediments were enriched with kaolinite from a detrital source due to denudation.[18]

Synthesis and genesis

Difficulties are encountered when trying to explain kaolinite formation under atmospheric conditions by extrapolation of thermodynamic data from the more successful high-temperature syntheses (as for example Meijer and Van der Plas, 1980[19] have pointed out). La Iglesia and Van Oosterwijk-Gastuche (1978)[20] thought that the conditions under which kaolinite will nucleate can be deduced from stability diagrams based as these are on dissolution data. Because of a lack of convincing results in their own experiments, La Iglesia and Van Oosterwijk-Gastuche (1978) had to conclude, however, that there were other, still unknown, factors involved in the low-temperature nucleation of kaolinite. Because of the observed very slow crystallization rates of kaolinite from solution at room temperature Fripiat and Herbillon (1971) postulated the existence of high activation energies in the low-temperature nucleation of kaolinite.

At high temperatures, equilibrium thermodynamic models appear to be satisfactory for the description of kaolinite dissolution and nucleation, because the thermal energy suffices to overcome the energy barriers involved in the nucleation process. The importance of syntheses at ambient temperature and atmospheric pressure towards the understanding of the mechanism involved in the nucleation of clay minerals lies in overcoming these energy barriers. As indicated by Caillère and Hénin (1960)[21] the processes involved will have to be studied in well-defined experiments, because it is virtually impossible to isolate the factors involved by mere deduction from complex natural physico-chemical systems such as the soil environment. Fripiat and Herbillon (1971),[22] in a review on the formation of kaolinite, raised the fundamental question how a disordered material (i.e., the amorphous fraction of tropical soils) could ever be transformed into a corresponding ordered structure. This transformation seems to take place in soils without major changes in the environment, in a relatively short period of time and at ambient temperature (and pressure).

Low-temperature synthesis of clay minerals (with kaolinite as an example) has several aspects. In the first place the silicic acid to be supplied to the growing crystal must be in a monomeric form, i.e., silica should be present in very dilute solution (Caillère et al., 1957;[23] Caillère and Hénin, 1960;[21] Wey and Siffert, 1962;[24] Millot, 1970[25]). In order to prevent the formation of amorphous silica gels precipitating from supersaturated solutions without reacting with the aluminium or magnesium cations to form crystalline silicates, the silicic acid must be present in concentrations below the maximum solubility of amorphous silica. The principle behind this prerequisite can be found in structural chemistry: "Since the polysilicate ions are not of uniform size, they cannot arrange themselves along with the metal ions into a regular crystal lattice" (Iler, 1955, p. 182[26]).

The second aspect of the low-temperature synthesis of kaolinite is that the aluminium cations must be hexacoordinated with respect to oxygen (Caillère and Hénin, 1947;[27] Caillère et al., 1953;[28] Hénin and Robichet, 1955[29]). Gastuche et al. (1962),[30] as well as Caillère and Hénin (1962) have concluded, that only in those instances when the aluminium hydroxide is in the form of gibbsite, kaolinite can ever be formed. If not, the precipitate formed will be a "mixed alumino-silicic gel" (as Millot, 1970, p. 343 put it). If this were the only requirement, large amounts of kaolinite could be harvested simply by adding gibbsite powder to a silica solution. Undoubtedly a marked degree of sorption of the silica in solution by the gibbsite surfaces will take place, but, as stated before, mere adsorption does not create the layer lattice typical of kaolinite crystals.

The third aspect is that these two initial components must be incorporated into one and the same mixed crystal with a layer structure. From the following equation (as given by Gastuche and DeKimpe, 1962)[31] for kaolinite formation

it can be seen, that five molecules of water must be removed from the reaction for every molecule of kaolinite formed. Field evidence illustrating the importance of the removal of water from the kaolinite reaction has been supplied by Gastuche and DeKimpe (1962). While studying soil formation on a basaltic rock in Kivu (Zaïre), Gastuche and DeKimpe noted how the occurrence of kaolinite depended on the "degrée de drainage" of the area involved. A clear distinction was found between areas with good drainage (i.e., areas with a marked difference between wet and dry seasons) and those areas with poor drainage (i.e., perennially swampy areas). Only in the areas with distinct seasonal alternations between wet and dry conditions kaolinite was found. The possible significance of alternating wet and dry conditions on the transition of allophane into kaolinite has been stressed by Tamura and Jackson (1953).[32] The role of alternations between wetting and drying on the formation of kaolinite has also been noted by Moore (1964).[33]

Laboratory syntheses

Syntheses of kaolinite at high temperatures (more than 100 °C [212 °F]) are relatively well known. There are for example the syntheses of Van Nieuwenberg and Pieters (1929);[34] Noll (1934);[35] Noll (1936);[36] Norton (1939);[37] Roy and Osborn (1954);[38] Roy (1961);[39] Hawkins and Roy (1962);[40] Tomura et al. (1985);[41] Satokawa et al. (1994)[42] and Huertas et al. (1999).[43] Relatively few low-temperature syntheses have become known (cf. Brindley and DeKimpe (1961);[44] DeKimpe (1969);[45] Bogatyrev et al. (1997)[46]).

Laboratory syntheses of kaolinite at room temperature and atmospheric pressure have been described by DeKimpe et al. (1961).[47] From those tests the role of periodicity becomes convincingly clear. For DeKimpe et al. (1961) had used daily additions of alumina (as AlCl
3
 · 6 H
2
O) and silica (in the form of ethyl silicate) during at least two months. In addition adjustments of the pH took place every day by way of adding either hydrochloric acid or sodium hydroxide. Such daily additions of Si and Al to the solution in combination with the daily titrations with hydrochloric acid or sodium hydroxide during at least 60 days will have introduced the necessary element of periodicity. Only now the actual role of what has been described as the "aging" (Alterung) of amorphous alumino-silicates (as for example Harder, 1978[48] had noted) can be fully understood. For time as such is not bringing about any change in a closed system at equilibrium, but a series of alternations, of periodically changing conditions (by definition taking place in an open system), will bring about the low-temperature formation of more and more of the stable phase kaolinite instead of (ill-defined) amorphous alumino-silicates.

Uses

The main use of the mineral kaolinite (about 50% of the time) is the production of paper; its use ensures the gloss on some grades of coated paper.[49]

Kaolin is also known for its capabilities to induce and accelerate blood clotting. In April 2008 the US Naval Medical Research Institute announced the successful use of a kaolinite-derived aluminosilicate infusion in traditional gauze, known commercially as QuikClot Combat Gauze,[50] which is still the hemostat of choice for all branches of the US military.

Kaolin is used (or was used in the past):

Geophagy

Humans sometimes eat kaolin for health or to suppress hunger,[56] a practice known as geophagy. Consumption is greater among women, especially during pregnancy.[57] This practice has also been observed within a small population of African-American women in the Southern United States, especially Georgia.[58][59] There, the kaolin is called white dirt, chalk or white clay.[58]

Safety

People can be exposed to kaolin in the workplace by breathing in the powder or from skin or eye contact.

United States

The Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for kaolin exposure in the workplace as 15 mg/m3 total exposure and 5 mg/m3 respiratory exposure over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 10 mg/m3 total exposure TWA 5 mg/m3 respiratory exposure over an 8-hour workday.[60]

See also

References

Citations

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  34. ^ van Nieuwenburg CJ, Pieters HA (1929). "Studies on hydrated aluminium silicates: I. The rehydration of metakaolin and the synthesis of kaolin". Recl. Trav. Chim. Pays-Bas. 48 (1): 27–36. doi:10.1002/recl.19290480106.
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  41. ^ Tomura S, Shibasaki Y, Mizuta H, et al. (1985). "Growth Conditions and Genesis of Spherical and Platy Kaolinite". Clays and Clay Minerals. 33 (3): 200–206. doi:10.1346/CCMN.1985.0330305.
  42. ^ Satokawa S, Osaki Y, Samejima S, et al. (1994). "Effects of the Structure of Silica-Alumina Gel on the Hydrothermal Synthesis of Kaolinite". Clays and Clay Minerals. 42 (3): 288–297. doi:10.1346/CCMN.1994.0420307.
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  45. ^ De Kimpe CR (1969). "Crystallization of kaolinite at low temperature from an alumino-silicic gel". Clays and Clay Minerals. 17 (1): 37–38. doi:10.1346/CCMN.1969.0170107.
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  50. ^ Rowe A (24 Apr 2008). "Nanoparticles Help Gauze Stop Gushing Wounds". Wired. Condé Nast. Archived from the original on 6 Jul 2009. Retrieved 5 Aug 2009.
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General references

  • Deer WA, Howie RA, Zussman J (1992). An introduction to the rock-forming minerals (2nd ed.). Harlow: Longman. ISBN 0582300940.
  • Hurlbut CS, Klein C (1985). Manual of mineralogy – after J. D. Dana (20th ed.). Wiley. pp. 428–429. ISBN 0471805807.
  • Breck DW (1984). Zeolite molecular sieves. Malabar, FL: R. E. Krieger Publishing Co. pp. 314–315. ISBN 0898746485.

External links

Allophane

Allophane is an amorphous to poorly crystalline hydrous aluminium silicate clay mineraloid. Its chemical formula is Al2O3·(SiO2)1.3-2·(2.5-3)H2O. Since it has short-range atomic order, it is a mineraloid, rather than a mineral, and can be identified by its distinctive infrared spectrum and its X-ray diffraction pattern. It was first described in 1816 in Gräfenthal, Thuringia, Germany. Allophane is a weathering or hydrothermal alteration product of volcanic glass and feldspars and sometimes has a composition similar to kaolinite but generally has a molar ratio of Al:Si = 2. It typically forms under mildly acidic to neutral pH (5-7). Its structure has been debated, but it is similar to clay minerals and is composed of curved alumina octahedral and silica tetrahedral layers. Transmission electron micrographs show that it is generally made up of aggregates of hollow spherules ~3-5 nm in diameter. Allophane can alter to form halloysite under resilicating aqueous conditions and can alter to form gibbsite under desilicating conditions. A copper containing variety cupro-allophane has been reported.

It forms waxy botryoidal to crusty masses with color varying from white through green, blue, yellow, to brown. It has a Mohs hardness of 3 and a specific gravity of 1.0.

It was named from the Greek allos - "other" and phanos - "to appear", as it gave a deceptive reaction in the blowpipe flame in old mineralogical testing.

Argillaceous minerals

Argillaceous minerals may appear silvery upon optical reflection and are minerals containing substantial amounts of clay-like components (Greek: ἄργιλλος = clay). Argillaceous components are fine-grained (less than 2 µm) aluminosilicates, and more particularly clay minerals such as kaolinite, montmorillonite-smectite, illite, and chlorite. Claystone and shales are thus predominantly argillaceous.

The adjective "argillaceous" is also used to define rocks in which clay minerals are a secondary but significant component. For example, argillaceous limestones are limestones consisting predominantly of calcium carbonate, but including 10-40% of clay minerals: such limestones, when soft, are often called marls. Similarly, argillaceous sandstones are sandstones consisting primarily of quartz grains, with the interstitial spaces filled with clay minerals.

Ball clay

Ball clays are kaolinitic sedimentary clays that commonly consist of 20–80% kaolinite, 10–25% mica, 6–65% quartz. Localized seams in the same deposit have variations in composition, including the quantity of the major minerals, accessory minerals and carbonaceous materials such as lignite. They are fine-grained and plastic in nature, and, unlike most earthenware clays, produce a fine quality white-coloured pottery body when fired, which is the key to their popularity with potters.

Ball clays are relatively scarce deposits due to the combination of geological factors needed for their formation and preservation. They are mined in parts of the Eastern United States and from three sites in Devon and Dorset in South West England. They are commonly used in the construction of many ceramic articles, where their primary role, apart from their white colour, is either to impart plasticity or to aid rheological stability during the shaping processes.

Bentonite

Bentonite () is an absorbent aluminium phyllosilicate clay consisting mostly of montmorillonite. It was named by Wilbur C. Knight in 1898 after the Cretaceous Benton Shale near Rock River, Wyoming.The different types of bentonite are each named after the respective dominant element, such as potassium (K), sodium (Na), calcium (Ca), and aluminium (Al). Experts debate a number of nomenclatorial problems with the classification of bentonite clays. Bentonite usually forms from weathering of volcanic ash, most often in the presence of water. However, the term bentonite, as well as a similar clay called tonstein, has been used to describe clay beds of uncertain origin. For industrial purposes, two main classes of bentonite exist: sodium and calcium bentonite. In stratigraphy and tephrochronology, completely devitrified (weathered volcanic glass) ash-fall beds are commonly referred to as K-bentonites when the dominant clay species is illite. In addition to montmorillonite and illite another common clay species that is sometimes dominant is kaolinite. Kaolinite-dominated clays are commonly referred to as tonsteins and are typically associated with coal.

Caliche

Caliche () is a sedimentary rock, a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or semiarid regions, including in central and western Australia, in the Kalahari Desert, in the High Plains of the western USA, in the Sonoran Desert and Mojave Desert, and in Eastern Saudi Arabia Al-Hasa. Caliche is also known as calcrete or kankar (in India). It belongs to the duricrusts. The term caliche is Spanish and is originally from the Latin calx, meaning lime.

Caliche is generally light-colored, but can range from white to light pink to reddish-brown, depending on the impurities present. It generally occurs on or near the surface, but can be found in deeper subsoil deposits, as well. Layers vary from a few inches to feet thick, and multiple layers can exist in a single location.

In northern Chile and Peru, caliche also refers to mineral deposits that include nitrate salts. Caliche can also refer to various claylike deposits in Mexico and Colombia. In addition, it has been used to describe some forms of quartzite, bauxite, kaolinite, laterite, chalcedony, opal, and soda niter.

A similar material, composed of calcium sulfate rather than calcium carbonate, is called gypcrust.

Clay minerals

Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces.

Clay minerals form in the presence of water and have been important to life, and many theories of abiogenesis involve them. They are important constituents of soils, and have been useful to humans since ancient times in agriculture and manufacturing.

Coated paper

Coated paper is paper which has been coated by a mixture of materials or a polymer to impart certain qualities to the paper, including weight, surface gloss, smoothness or reduced ink absorbency. Various materials, including Kaolinite, calcium carbonate, Bentonite, and talc can be used to coat paper for high quality printing used in packaging industry and in magazines. The chalk or china clay is bound to the paper with synthetic viscosifiers, such as styrene-butadiene latexes and natural organic binders such as starch. The coating formulation may also contain chemical additives as dispersants, resins, or polyethylene to give water resistance and wet strength to the paper, or to protect against ultraviolet radiation.

Death Busters

The Death Busters (デスバスターズ, Desu Basutāzu) are a group of fictional characters who serve as antagonists in the Sailor Moon manga series written by Naoko Takeuchi. This group comprises the antagonists of the third major story arc, which is called the Infinity in the manga and Sailor Moon S in the anime. They are first introduced in chapter #24 "Infinity 1 – Premonition", originally published in Japan on July 7, 1994. In the Cloverway English adaptation, they are called the "Heart Snatchers".

Originally from the "Tau Ceti Star System" in another dimension, the Death Busters acquire human host bodies to act through with Kaolinite and Professor Tomoe as acting leaders. Based in Mugen Academy (無限学園, Mugen Gakuen, Literally "Infinity Academy"), an elite high school built in the middle of Tokyo's Sankakusu District (三角州区, Sankakusu-ku, Literally "Delta District"), the Death Busters work to gather human souls which would prolong their dying homeworld. Their ultimate goal is the revival of their commander Mistress 9 so they can bring their master Pharaoh 90 to Earth and terraform it into a new home at the cost of the current life forms.

Gover Stream

The Gover Stream (Cornish: Gover, meaning stream) is an approximately 3 kilometres (1.9 mi) long stream located in mid south Cornwall, England, United Kingdom.

The source of the stream is at the north eastern side of Blackpool China clay pit at grid reference SW 980 540 . The stream flows south east through the Gover Valley into the town of St Austell where it joins the St Austell River or "White River". The Gover Stream is the first of the two largest tributaries of the St Austell River.

Rivers in the area have problems with china clay waste materials, mostly kaolinite, entering the rivers and turning them white. This led to the locally named "White River". (Kaolinite is not a waste material of the quarrying process, but economically not all of the kaolin can be extracted). Suspended particles in the stream are reduced by approximately 98% by settling tanks at the beginning of the river. This reduces the energy of the water in the tanks and allows suspended particles to be deposited and later dredged by diggers.

Several disused china clay dries are located along the stream showing its past industrial importance. There were also plans to extend the Pentewan railway along the valley from St Austell, but they did not come to fruition.

Recently the Gover Valley has been under threat due to a plan to use the valley as a tipping site for china clay waste. Waste is a huge problem in the area as for every tonne of kaolinite produced there are on average nine tonnes of waste materials produced; this amounts to approximately 20 million tonnes of waste materials per year. An area of 1 square kilometre (250 acres) is planned to be tipped on which would destroy the upper section of the Gover Stream as well as ancient farmland and woodland. The tip will be landscaped once completed.

Greenalite

Greenalite is a mineral in the kaolinite-serpentine group with the chemical composition (Fe2+,Fe3+)2-3Si2O5OH4. It is a member of the serpentine group.

Kaopectate

Kaopectate is an orally taken medication from Chattem, Inc. for the treatment of mild diarrhea. It is also sometimes used to treat indigestion, nausea and stomach ulcers. The active ingredients have varied over time, and are different between the United States and Canada. The original active ingredients were kaolinite and pectin. In the US, the active ingredient is now bismuth subsalicylate (the same as in Pepto-Bismol). In Switzerland, attapulgite its used.

Kyanite

Kyanite is typically a blue aluminosilicate mineral, usually found in aluminium-rich metamorphic pegmatites and/or sedimentary rock or the lava zone. Kyanite in metamorphic rocks generally indicates pressures higher than four kilobars. It is commonly found in quartz.

Although potentially stable at lower pressure and low temperature, the activity of water is usually high enough under such conditions that it is replaced by hydrous aluminosilicates such as muscovite, pyrophyllite, or kaolinite. Kyanite is also known as disthene, rhaeticite and cyanite.

Kyanite is a member of the aluminosilicate series, which also includes the polymorph andalusite and the polymorph sillimanite. Kyanite is strongly anisotropic, in that its hardness varies depending on its crystallographic direction. In kyanite, this anisotropism can be considered an identifying characteristic.

At temperatures above 1100 °C kyanite decomposes into mullite and vitreous silica via the following reaction: 3(Al2O3·SiO2) → 3Al2O3·2SiO2 + SiO2. This transformation results in an expansion.Its name comes from the same origin as that of the color cyan, being derived from the Ancient Greek word κύανος. This is generally rendered into English as kyanos or kuanos and means "dark blue".

List of countries by bauxite production

Bauxite is the most important aluminum ore. This form of rock consists mostly of the minerals gibbsite Al(OH)3, boehmite γ-AlO(OH), and diaspore α-AlO(OH), in a mixture that usually includes the two iron oxides goethite and hematite, and may include the clay mineral kaolinite, and small amounts of the titanium minerals anatase TiO2, Ilmenite, FeTiO3, and FeOTiO2.

Bauxite was named after the village Les Baux in southern France, where it was first recognised as containing aluminium and named by the French geologist Pierre Berthier in 1821.

List of countries by bentonite production

Bentonite is an absorbent aluminium phyllosilicate generally impure clay consisting mostly of montmorillonite. There are a few types of bentonites and their names depend on the dominant elements, such as potassium, sodium, calcium, and aluminium. As noted in several places in the geologic literature, there are some nomenclatorial problems with the classification of bentonite clays.

Bentonite usually forms from weathering of volcanic ash, most often in the presence of water. However, the term bentonite, as well as a similar clay called tonstein, have been used for clay beds of uncertain origin. For industrial purposes, two main classes of bentonite exist: sodium bentonite and calcium bentonite.

In stratigraphy and tephrochronology, completely devitrified (weathered volcanic glass) ash-fall beds are commonly referred to as K-bentonites when the dominant clay species is illite. Other common clay species, and sometimes dominant, are montmorillinite and kaolinite. Kaolinite dominated clays are commonly referred to as tonsteins and are typically associated with coal.

Metakaolin

Metakaolin is the anhydrous calcined form of the clay mineral kaolinite. Minerals that are rich in kaolinite are known as china clay or kaolin, traditionally used in the manufacture of porcelain. The particle size of metakaolin is smaller than cement particles, but not as fine as silica fume.

Nacrite

Nacrite Al2Si2O5(OH)4 is a clay mineral that is polymorphous (or polytypic) with kaolinite. It crystallizes in the monoclinic system. X-ray diffraction analysis is required for positive identification.

Nacrite was first described in 1807 for an occurrence in Saxony, Germany. The name is from nacre in reference to the mother of pearl luster of nacrite masses.

Nili Fossae

Nili Fossae is a group of large, concentric grabens on Mars, located in the Syrtis Major quadrangle. They have been eroded and partly filled in by sediments and clay-rich ejecta from a nearby giant impact crater, the Isidis basin. It is located at approximately 22°N, 75°E, and has an elevation of −0.6 km (−0.37 mi). Nili Fossae was on the list of potential landing sites of the Mars Science Laboratory, arriving in 2012, but was dropped before the final four sites were determined. Although not among the last finalists, in September 2015 it was selected as a potential landing site for the Mars 2020 rover, which will use the same design as Curiosity, but with a different payload focused on astrobiology.

A large exposure of olivine is located in Nili Fossae. In December 2008, NASA's Mars Reconnaissance Orbiter found that rocks at Nili Fossae contain carbonate minerals, a geologically significant discovery. Other minerals found by MRO are aluminum smectite, iron/magnesium smecite, hydrated silica, kaolinite group minerals, and iron oxides. NASA scientists discovered that Nili Fossae is the source of plumes of methane, raising the question of whether this source originates from biological sources.Researchers in July 2010 suggested that carbonate bearing rocks found in the Nili Fossae region of Mars are made up of hydrothermally altered ultramafic rocks. Consequently, hydrothermal activity would have provided sufficient energy for biological activity. Evidence of living organisms could have been preserved.Nili Fossae trough is thought to have resulted from the impact that formed the nearby Isidis basin.

Nili Fossae Trough was one of seven finalists for the MSL landing site:

Eberswalde Crater

Gale Crater

Holden Crater

Mawrth Vallis

Miyamoto Crater

Nili Fossae Trough

Southern Meridiani

Nitisol

A Nitisol in the World Reference Base for Soil Resources (WRB) is a deep, red, well-drained soil with a clay content of more than 30% and a blocky structure. Nitisols correlate with the Kandic Alfisols, Ultisols and Inceptisols of the USDA soil taxonomy.These soils are found in the tropics and subtropics; there are extensive areas of them in the tropical highlands of Ethiopia, Kenya, Democratic Republic of the Congo and Cameroon. Nitisols form from fine-textured material weathered from intermediate to basic parent rock and kaolinite, halloysite and iron oxides dominate their clay mineralogy.

The natural vegetation on nitisols includes tropical rain forest and savannah. Limitations frequently include low phosphorus availability and low base status, but once ameliorated, these deep, stable soils have high agricultural potential, and are often planted to crops.

Népouite

Népouite is a rare nickel silicate mineral which has the apple green colour typical of such compounds. It was named by E Glasser in 1907 after the place where it was first described (the type locality), the Népoui Mine, Népoui, Nouméa Commune, North Province, New Caledonia. The ideal formula is Ni3(Si2O5)(OH)4, but most specimens contain some magnesium, and (Ni,Mg)3(Si2O5)(OH)4 is more realistic. There is a similar mineral called lizardite (named after the Lizard Complex in Cornwall, England) in which all of the nickel is replaced by magnesium, formula Mg3(Si2O5)(OH)4. These two minerals form a series; intermediate compositions are possible, with varying proportions of nickel to magnesium.Pecoraite is another rare mineral with the same chemical formula as népouite, but a different structure; such minerals are said to be dimorphs of each other, in the same way as graphite is a dimorph of diamond. Népouite, lizardite and pecoraite are all members of the kaolinite-serpentine group.Garnierite is a green nickel ore that formed as a result of weathering of ultramafic rocks, and that occurs in many nickel deposits worldwide. It is a mixture of various nickel and magnesium phyllosilicates (sheet silicates), including népouite. Associated minerals include calcite, chlorite, goethite, halloysite, nontronite, pimelite, quartz, sepiolite, serpentine, talc and willemseite.

As well as the type locality in New Caledonia, it has been found in Australia, Austria, the Czech Republic, the Democratic Republic of Congo, Germany, Greece, Italy, Japan, Morocco, Poland, Russia, South Africa and the US.

Transcriptions
Standard Mandarin
Hanyu PinyinGāolǐng shí
Wade–GilesKao1-ling3 shih2
IPA[káu.lìŋ ʂɨ̌]
Micas
Talcs
Pyrophyllite series
Kaolinites
Serpentines
Corrensites
Smectites and vermiculite family
Chlorites
Allophanes
Sepiolites
Pyrosmalites
Stilpnomelanes

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