British Aluminium was an aluminium production company. It was originally formed as the British Aluminium Company Ltd on 7 May 1894 and was subsequently known as British Alcan Aluminium plc (1982-1996).
91-494: In the late 1880s and early 1890s, innovations in the extraction of alumina from ore ( bauxite ) and of converting this into aluminium by electrolysis had precipitated a drastic fall in the price of the metal. The electrolytic process required large amounts of electricity, which could be easily and cheaply provided by hydro-electric power in the Scottish Highlands . The first aluminium ingots were produced at Foyers in
182-585: A bend in the middle that is caused by start of the twin. Penetration twins consist of two single crystals that have grown into each other; examples of this twinning include cross-shaped staurolite twins and Carlsbad twinning in orthoclase. Cyclic twins are caused by repeated twinning around a rotation axis. This type of twinning occurs around three, four, five, six, or eight-fold axes, and the corresponding patterns are called threelings, fourlings, fivelings , sixlings, and eightlings. Sixlings are common in aragonite. Polysynthetic twins are similar to cyclic twins through
273-417: A bigger coordination numbers because of the increase in relative size as compared to oxygen (the last orbital subshell of heavier atoms is different too). Changes in coordination numbers leads to physical and mineralogical differences; for example, at high pressure, such as in the mantle , many minerals, especially silicates such as olivine and garnet , will change to a perovskite structure , where silicon
364-432: A chemical compound occurs naturally with different crystal structures, each structure is considered a different mineral species. Thus, for example, quartz and stishovite are two different minerals consisting of the same compound, silicon dioxide . The International Mineralogical Association (IMA) is the generally recognized standard body for the definition and nomenclature of mineral species. As of November 2024 ,
455-456: A coating on aluminium by anodizing or by plasma electrolytic oxidation (see the "Properties" above). Both the hardness and abrasion-resistant characteristics of the coating originate from the high strength of aluminium oxide, yet the porous coating layer produced with conventional direct current anodizing procedures is within a 60–70 Rockwell hardness C range which is comparable only to hardened carbon steel alloys, but considerably inferior to
546-470: A distinct mineral: The details of these rules are somewhat controversial. For instance, there have been several recent proposals to classify amorphous substances as minerals, but they have not been accepted by the IMA. The IMA is also reluctant to accept minerals that occur naturally only in the form of nanoparticles a few hundred atoms across, but has not defined a minimum crystal size. Some authors require
637-499: A fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form. The geological definition of mineral normally excludes compounds that occur only in living organisms. However, some minerals are often biogenic (such as calcite ) or organic compounds in the sense of chemistry (such as mellite ). Moreover, living organisms often synthesize inorganic minerals (such as hydroxylapatite ) that also occur in rocks. The concept of mineral
728-463: A key to defining a substance as a mineral. A 2011 article defined icosahedrite , an aluminium-iron-copper alloy, as a mineral; named for its unique natural icosahedral symmetry , it is a quasicrystal . Unlike a true crystal, quasicrystals are ordered but not periodic. A rock is an aggregate of one or more minerals or mineraloids. Some rocks, such as limestone or quartzite , are composed primarily of one mineral – calcite or aragonite in
819-457: A manual dermal abrasive used according to manufacturer directions. Aluminium oxide flakes are used in paint for reflective decorative effects, such as in the automotive or cosmetic industries. Aluminium oxide is a representative of bioinert ceramics. Due to its excellent biocompatibility, high strength, and wear resistance, alumina ceramics are used in medical applications to manufacture artificial bones and joints. In this case, aluminium oxide
910-405: A material in hip replacements and birth control pills . It is used as a scintillator and dosimeter for radiation protection and therapy applications for its optically stimulated luminescence properties. Insulation for high-temperature furnaces is often manufactured from aluminium oxide. Sometimes the insulation has varying percentages of silica depending on the temperature rating of
1001-409: A mineral defines how much it can resist scratching or indentation. This physical property is controlled by the chemical composition and crystalline structure of a mineral. The most commonly used scale of measurement is the ordinal Mohs hardness scale, which measures resistance to scratching. Defined by ten indicators, a mineral with a higher index scratches those below it. The scale ranges from talc,
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#17328583066691092-545: A proportion of aluminium in the alloy to enhance corrosion resistance. The aluminium oxide generated by anodising is typically amorphous , but discharge-assisted oxidation processes such as plasma electrolytic oxidation result in a significant proportion of crystalline aluminium oxide in the coating, enhancing its hardness . Aluminium oxide was taken off the United States Environmental Protection Agency 's chemicals lists in 1988. Aluminium oxide
1183-412: A relatively high thermal conductivity ( 30 Wm K ) for a ceramic material. Aluminium oxide is insoluble in water. In its most commonly occurring crystalline form, called corundum or α-aluminium oxide, its hardness makes it suitable for use as an abrasive and as a component in cutting tools . Aluminium oxide is responsible for the resistance of metallic aluminium to weathering . Metallic aluminium
1274-467: A research field of interest. Some body armors utilize alumina ceramic plates, usually in combination with aramid or UHMWPE backing to achieve effectiveness against most rifle threats. Alumina ceramic armor is readily available to most civilians in jurisdictions where it is legal, but is not considered military grade. It is also used to produce bullet-proof alumina glass capable to withstand impact of .50 BMG calibre rounds. Aluminium oxide can be grown as
1365-432: A sedimentary mineral, and silicic acid ): Under low-grade metamorphic conditions, kaolinite reacts with quartz to form pyrophyllite (Al 2 Si 4 O 10 (OH) 2 ): As metamorphic grade increases, the pyrophyllite reacts to form kyanite and quartz: Alternatively, a mineral may change its crystal structure as a consequence of changes in temperature and pressure without reacting. For example, quartz will change into
1456-472: A tailored product. The type of phases present affects, for example, the solubility and pore structure of the aluminium oxide product which, in turn, affects the cost of aluminium production and pollution control. The Sintering Process is a high-temperature method primarily used when the Bayer Process is not suitable, especially for ores with high silica content or when a more controlled product morphology
1547-406: A tetrahedral fashion; on the other hand, graphite is composed of sheets of carbons in sp hybrid orbitals, where each carbon is bonded covalently to only three others. These sheets are held together by much weaker van der Waals forces , and this discrepancy translates to large macroscopic differences. Twinning is the intergrowth of two or more crystals of a single mineral species. The geometry of
1638-935: A variety of its SiO 2 polymorphs , such as tridymite and cristobalite at high temperatures, and coesite at high pressures. Classifying minerals ranges from simple to difficult. A mineral can be identified by several physical properties, some of them being sufficient for full identification without equivocation. In other cases, minerals can only be classified by more complex optical , chemical or X-ray diffraction analysis; these methods, however, can be costly and time-consuming. Physical properties applied for classification include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, cleavage and fracture, and specific gravity. Other less general tests include fluorescence , phosphorescence , magnetism , radioactivity , tenacity (response to mechanical induced changes of shape or form), piezoelectricity and reactivity to dilute acids . Crystal structure results from
1729-498: A variety of minerals because of the need to balance charges. Because the eight most common elements make up over 98% of the Earth's crust, the small quantities of the other elements that are typically present are substituted into the common rock-forming minerals. The distinctive minerals of most elements are quite rare, being found only where these elements have been concentrated by geological processes, such as hydrothermal circulation , to
1820-595: A white mica, can be used for windows (sometimes referred to as isinglass), as a filler, or as an insulator. Ores are minerals that have a high concentration of a certain element, typically a metal. Examples are cinnabar (HgS), an ore of mercury; sphalerite (ZnS), an ore of zinc; cassiterite (SnO 2 ), an ore of tin; and colemanite , an ore of boron . Gems are minerals with an ornamental value, and are distinguished from non-gems by their beauty, durability, and usually, rarity. There are about 20 mineral species that qualify as gem minerals, which constitute about 35 of
1911-466: Is a favored filler for plastics. Aluminium oxide is a common ingredient in sunscreen and is often also present in cosmetics such as blush, lipstick, and nail polish. Many formulations of glass have aluminium oxide as an ingredient. Aluminosilicate glass is a commonly used type of glass that often contains 5% to 10% alumina. Aluminium oxide catalyses a variety of reactions that are useful industrially. In its largest scale application, aluminium oxide
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#17328583066692002-707: Is a sedimentary rock composed primarily of organically derived carbon. In rocks, some mineral species and groups are much more abundant than others; these are termed the rock-forming minerals. The major examples of these are quartz, the feldspars , the micas , the amphiboles , the pyroxenes , the olivines , and calcite; except for the last one, all of these minerals are silicates. Overall, around 150 minerals are considered particularly important, whether in terms of their abundance or aesthetic value in terms of collecting. Commercially valuable minerals and rocks, other than gemstones, metal ores, or mineral fuels, are referred to as industrial minerals . For example, muscovite ,
2093-566: Is derived, are used in the manufacture of zeolites , coating titania pigments, and as a fire retardant/smoke suppressant. Over 90% of aluminium oxide, termed smelter grade alumina (SGA), is consumed for the production of aluminium, usually by the Hall–Héroult process . The remainder, termed specialty alumina , is used in a wide variety of applications which take advantage of its inertness, temperature resistance and electrical resistance. Being fairly chemically inert and white, aluminium oxide
2184-428: Is distinct from rock , which is any bulk solid geologic material that is relatively homogeneous at a large enough scale. A rock may consist of one type of mineral or may be an aggregate of two or more different types of minerals, spacially segregated into distinct phases . Some natural solid substances without a definite crystalline structure, such as opal or obsidian , are more properly called mineraloids . If
2275-445: Is in octahedral coordination. Other examples are the aluminosilicates kyanite , andalusite , and sillimanite (polymorphs, since they share the formula Al 2 SiO 5 ), which differ by the coordination number of the Al ; these minerals transition from one another as a response to changes in pressure and temperature. In the case of silicate materials, the substitution of Si by Al allows for
2366-455: Is on the EPA's Toxics Release Inventory list if it is a fibrous form. Aluminium oxide is an amphoteric substance, meaning it can react with both acids and bases , such as hydrofluoric acid and sodium hydroxide , acting as an acid with a base and a base with an acid, neutralising the other and producing a salt. The most common form of crystalline aluminium oxide is known as corundum , which
2457-408: Is possible for one element to be substituted for another. Chemical substitution will occur between ions of a similar size and charge; for example, K will not substitute for Si because of chemical and structural incompatibilities caused by a big difference in size and charge. A common example of chemical substitution is that of Si by Al , which are close in charge, size, and abundance in the crust. In
2548-470: Is possible for two rocks to have an identical or a very similar bulk rock chemistry without having a similar mineralogy. This process of mineralogical alteration is related to the rock cycle . An example of a series of mineral reactions is illustrated as follows. Orthoclase feldspar (KAlSi 3 O 8 ) is a mineral commonly found in granite , a plutonic igneous rock . When exposed to weathering, it reacts to form kaolinite (Al 2 Si 2 O 5 (OH) 4 ,
2639-456: Is required. Firstly, Bauxite is mixed with additives like limestone and soda ash, then heating the mixture at high temperatures (1200 °C to 1500 °C) to form sodium aluminate and calcium silicate . After sintering, the material is leached with water to dissolve the sodium aluminate , leaving behind impurities. Sodium aluminate is then precipitated from the solution and calcined at around 1000 °C to produce alumina. This method
2730-524: Is the angle opposite the a-axis, viz. the angle between the b and c axes): The hexagonal crystal family is also split into two crystal systems – the trigonal , which has a three-fold axis of symmetry, and the hexagonal, which has a six-fold axis of symmetry. Chemistry and crystal structure together define a mineral. With a restriction to 32 point groups, minerals of different chemistry may have identical crystal structure. For example, halite (NaCl), galena (PbS), and periclase (MgO) all belong to
2821-483: Is the catalyst in the Claus process for converting hydrogen sulfide waste gases into elemental sulfur in refineries. It is also useful for dehydration of alcohols to alkenes . Aluminium oxide serves as a catalyst support for many industrial catalysts, such as those used in hydrodesulfurization and some Ziegler–Natta polymerizations. Aluminium oxide is widely used to remove water from gas streams. Aluminium oxide
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2912-405: Is the hardest natural substance, has an adamantine lustre, and belongs to the isometric crystal family, whereas graphite is very soft, has a greasy lustre, and crystallises in the hexagonal family. This difference is accounted for by differences in bonding. In diamond, the carbons are in sp hybrid orbitals, which means they form a framework where each carbon is covalently bonded to four neighbours in
3003-565: Is the thermodynamically stable form. The oxygen ions form a nearly hexagonal close-packed structure with the aluminium ions filling two-thirds of the octahedral interstices. Each Al center is octahedral . In terms of its crystallography , corundum adopts a trigonal Bravais lattice with a space group of R 3 c (number 167 in the International Tables). The primitive cell contains two formula units of aluminium oxide. Aluminium oxide also exists in other metastable phases, including
3094-456: Is typical of garnet, prismatic (elongated in one direction), and tabular, which differs from bladed habit in that the former is platy whereas the latter has a defined elongation. Related to crystal form, the quality of crystal faces is diagnostic of some minerals, especially with a petrographic microscope. Euhedral crystals have a defined external shape, while anhedral crystals do not; those intermediate forms are termed subhedral. The hardness of
3185-419: Is used as a superior polishing abrasive in watchmaking and clockmaking. Aluminium oxide is also used in the coating of stanchions in the motocross and mountain bike industries. This coating is combined with molybdenumdisulfate to provide long term lubrication of the surface. Mineral In geology and mineralogy , a mineral or mineral species is, broadly speaking, a solid substance with
3276-538: Is used as an insulating barrier in capacitors . In lighting, translucent aluminium oxide is used in some sodium vapor lamps . Aluminium oxide is also used in preparation of coating suspensions in compact fluorescent lamps . In chemistry laboratories, aluminium oxide is a medium for chromatography , available in basic (pH 9.5), acidic (pH 4.5 when in water) and neutral formulations. Additionally, small pieces of aluminium oxide are often used as boiling chips . Health and medical applications include it as
3367-495: Is used for its hardness and strength. Its naturally occurring form, corundum , is a 9 on the Mohs scale of mineral hardness (just below diamond). It is widely used as an abrasive , including as a much less expensive substitute for industrial diamond . Many types of sandpaper use aluminium oxide crystals. In addition, its low heat retention and low specific heat make it widely used in grinding operations, particularly cutoff tools. As
3458-409: Is used to coat the surfaces of medical implants to give biocompatibility and corrosion resistance. It is also used for manufacturing dental implants, joint replacements, and other medical devices. Aluminium oxide has been used in a few experimental and commercial fiber materials for high-performance applications (e.g., Fiber FP, Nextel 610, Nextel 720). Alumina nanofibers in particular have become
3549-420: Is used to manufacture tiles which are attached inside pulverized fuel lines and flue gas ducting on coal fired power stations to protect high wear areas. They are not suitable for areas with high impact forces as these tiles are brittle and susceptible to breakage. Aluminium oxide is an electrical insulator used as a substrate ( silicon on sapphire ) for integrated circuits , but also as a tunnel barrier for
3640-600: Is useful for the production of complex shapes and can be used to create porous or dense materials. Known as alpha alumina in materials science , and as alundum (in fused form) or aloxite in mining and ceramic communities, aluminium oxide finds wide use. Annual global production of aluminium oxide in 2015 was approximately 115 million tonnes , over 90% of which was used in the manufacture of aluminium metal. The major uses of speciality aluminium oxides are in refractories, ceramics, polishing and abrasive applications. Large tonnages of aluminium hydroxide, from which alumina
3731-436: Is very reactive with atmospheric oxygen, and a thin passivation layer of aluminium oxide (4 nm thickness) forms on any exposed aluminium surface in a matter of hundreds of picoseconds. This layer protects the metal from further oxidation. The thickness and properties of this oxide layer can be enhanced using a process called anodising . A number of alloys , such as aluminium bronzes , exploit this property by including
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3822-614: The CIPW norm , which gives reasonable estimates for volcanic rock formed from dry magma. The chemical composition may vary between end member species of a solid solution series. For example, the plagioclase feldspars comprise a continuous series from sodium -rich end member albite (NaAlSi 3 O 8 ) to calcium -rich anorthite (CaAl 2 Si 2 O 8 ) with four recognized intermediate varieties between them (given in order from sodium- to calcium-rich): oligoclase , andesine , labradorite , and bytownite . Other examples of series include
3913-678: The Gold Coast (now Ghana ), in 1928. The company produced carbon at three different sites in Scotland and owned four rolling mills in England . In the 1940s and '50s the company opened and/or invested in aluminium plants and infrastructure in Norway , India , Canada , British Guiana and acquired further bauxite resources in Australia . In 1958, however, finance problems led to the company being taken over by
4004-410: The chemical formula Al 2 O 3 . It is the most commonly occurring of several aluminium oxides , and specifically identified as aluminium oxide . It is commonly called alumina and may also be called aloxide , aloxite , or alundum in various forms and applications. It occurs naturally in its crystalline polymorphic phase α-Al 2 O 3 as the mineral corundum , varieties of which form
4095-496: The hydrosphere , atmosphere , and biosphere . The group's scope includes mineral-forming microorganisms, which exist on nearly every rock, soil, and particle surface spanning the globe to depths of at least 1600 metres below the sea floor and 70 kilometres into the stratosphere (possibly entering the mesosphere ). Biogeochemical cycles have contributed to the formation of minerals for billions of years. Microorganisms can precipitate metals from solution , contributing to
4186-473: The olivine group . Besides the essential chemical composition and crystal structure, the description of a mineral species usually includes its common physical properties such as habit , hardness , lustre , diaphaneity , colour, streak , tenacity , cleavage , fracture , parting, specific gravity , magnetism , fluorescence , radioactivity , as well as its taste or smell and its reaction to acid . Minerals are classified by key chemical constituents;
4277-466: The "aluminum plate, sheet and soft-alloy extrusion manufacturing operations and distribution businesses" of British Aluminium in 2000 from Luxfer Group who retained some of the business. Alcoa decided to close the site at Dolgarrog in North Wales in 2002. Dolgarrog Aluminium Ltd formed and the local government tried to finance saving the nearly 200 jobs there. After five years as of October 2007, during
4368-451: The 78 mineral classes listed in the Dana classification scheme. Skinner's (2005) definition of a mineral takes this matter into account by stating that a mineral can be crystalline or amorphous. Although biominerals are not the most common form of minerals, they help to define the limits of what constitutes a mineral proper. Nickel's (1995) formal definition explicitly mentioned crystallinity as
4459-417: The Al are surrounded by 4 oxygen neighbors), and 1/3 5-coordinated, with very little (<5%) octahedral Al-O present. Around 80% of the oxygen atoms are shared among three or more Al-O polyhedra, and the majority of inter-polyhedral connections are corner-sharing, with the remaining 10–20% being edge-sharing. The breakdown of octahedra upon melting is accompanied by a relatively large volume increase (~33%),
4550-585: The American Reynolds Metals and TI Group . Despite overcapacity during the 1960s, a large smelter built on the promise of cheap nuclear generated electricity commenced production in Invergordon in 1971; this plant would close eleven years later. The company was bought again by the Canadian-based Alcan in 1982. Operations were merged and the company was renamed British Alcan Ltd. In 1994,
4641-474: The IMA recognizes 6,100 official mineral species. The chemical composition of a named mineral species may vary somewhat due to the inclusion of small amounts of impurities. Specific varieties of a species sometimes have conventional or official names of their own. For example, amethyst is a purple variety of the mineral species quartz . Some mineral species can have variable proportions of two or more chemical elements that occupy equivalent positions in
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#17328583066694732-431: The IMA's decision to exclude biogenic crystalline substances. For example, Lowenstam (1981) stated that "organisms are capable of forming a diverse array of minerals, some of which cannot be formed inorganically in the biosphere." Skinner (2005) views all solids as potential minerals and includes biominerals in the mineral kingdom, which are those that are created by the metabolic activities of organisms. Skinner expanded
4823-455: The IMA. They are most commonly named after a person , followed by discovery location; names based on chemical composition or physical properties are the two other major groups of mineral name etymologies. Most names end in "-ite"; the exceptions are usually names that were well-established before the organization of mineralogy as a discipline, for example galena and diamond . A topic of contention among geologists and mineralogists has been
4914-548: The Latin species , "a particular sort, kind, or type with distinct look, or appearance". The abundance and diversity of minerals is controlled directly by their chemistry, in turn dependent on elemental abundances in the Earth. The majority of minerals observed are derived from the Earth's crust . Eight elements account for most of the key components of minerals, due to their abundance in the crust. These eight elements, summing to over 98% of
5005-488: The aluminium abundance is unusually high, the excess aluminium will form muscovite or other aluminium-rich minerals. If silicon is deficient, part of the feldspar will be replaced by feldspathoid minerals. Precise predictions of which minerals will be present in a rock of a particular composition formed at a particular temperature and pressure requires complex thermodynamic calculations. However, approximate estimates may be made using relatively simple rules of thumb , such as
5096-499: The basic mixture, Fe 2 O 3 is removed. When the Bayer liquor is cooled, Al(OH) 3 precipitates, leaving the silicates in solution. The solid Al(OH) 3 Gibbsite is then calcined (heated to over 1100 °C) to give aluminium oxide: The product aluminium oxide tends to be multi-phase, i.e., consisting of several phases of aluminium oxide rather than solely corundum . The production process can therefore be optimized to produce
5187-449: The bulk chemistry of the parent body. For example, in most igneous rocks, the aluminium and alkali metals (sodium and potassium) that are present are primarily found in combination with oxygen, silicon, and calcium as feldspar minerals. However, if the rock is unusually rich in alkali metals, there will not be enough aluminium to combine with all the sodium as feldspar, and the excess sodium will form sodic amphiboles such as riebeckite . If
5278-424: The case of limestone, and quartz in the latter case. Other rocks can be defined by relative abundances of key (essential) minerals; a granite is defined by proportions of quartz, alkali feldspar , and plagioclase feldspar . The other minerals in the rock are termed accessory minerals , and do not greatly affect the bulk composition of the rock. Rocks can also be composed entirely of non-mineral material; coal
5369-429: The chemical exchange between trimethylaluminium (Al(CH 3 ) 3 ) and H 2 O: H 2 O in the above reaction can be replaced by ozone (O 3 ) as the active oxidant and the following reaction then takes place: The Al 2 O 3 films prepared using O 3 show 10–100 times lower leakage current density compared with those prepared by H 2 O. Aluminium oxide, being a dielectric with relatively large band gap ,
5460-424: The company produced 357,000 tonnes of aluminium and made a pre-tax profit of £30.9m up from a loss of £22.7m the previous year. In February 1996 it was announced that Alcan was to sell British Alcan to a group of institutional investors, Mercury Development Capital , Morgan Grenfell Development Capital and CVC Capital Partners for £300m. The new company would be known as British Aluminium Ltd. Alcoa acquired
5551-415: The coordination of the silicate is by a number: in the case of the silica tetrahedron, the silicon is said to have a coordination number of 4. Various cations have a specific range of possible coordination numbers; for silicon, it is almost always 4, except for very high-pressure minerals where the compound is compressed such that silicon is in six-fold (octahedral) coordination with oxygen. Bigger cations have
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#17328583066695642-417: The crust by weight, are, in order of decreasing abundance: oxygen , silicon , aluminium , iron , magnesium , calcium , sodium and potassium . Oxygen and silicon are by far the two most important – oxygen composes 47% of the crust by weight, and silicon accounts for 28%. The minerals that form are those that are most stable at the temperature and pressure of formation, within the limits imposed by
5733-427: The cubic γ and η phases, the monoclinic θ phase, the hexagonal χ phase, the orthorhombic κ phase and the δ phase that can be tetragonal or orthorhombic. Each has a unique crystal structure and properties. Cubic γ-Al 2 O 3 has important technical applications. The so-called β-Al 2 O 3 proved to be NaAl 11 O 17 . Molten aluminium oxide near the melting temperature is roughly 2/3 tetrahedral (i.e. 2/3 of
5824-405: The density of the liquid close to its melting point is 2.93 g/cm . The structure of molten alumina is temperature dependent and the fraction of 5- and 6-fold aluminium increases during cooling (and supercooling), at the expense of tetrahedral AlO 4 units, approaching the local structural arrangements found in amorphous alumina. Aluminium hydroxide minerals are the main component of bauxite ,
5915-434: The difference in charge has to accounted for by making a second substitution of Si by Al . Coordination polyhedra are geometric representations of how a cation is surrounded by an anion. In mineralogy, coordination polyhedra are usually considered in terms of oxygen, due its abundance in the crust. The base unit of silicate minerals is the silica tetrahedron – one Si surrounded by four O . An alternate way of describing
6006-414: The dipyramidal point group. These differences arise corresponding to how aluminium is coordinated within the crystal structure. In all minerals, one aluminium ion is always in six-fold coordination with oxygen. Silicon, as a general rule, is in four-fold coordination in all minerals; an exception is a case like stishovite (SiO 2 , an ultra-high pressure quartz polymorph with rutile structure). In kyanite,
6097-517: The example of plagioclase, there are three cases of substitution. Feldspars are all framework silicates, which have a silicon-oxygen ratio of 2:1, and the space for other elements is given by the substitution of Si by Al to give a base unit of [AlSi 3 O 8 ] ; without the substitution, the formula would be charge-balanced as SiO 2 , giving quartz. The significance of this structural property will be explained further by coordination polyhedra. The second substitution occurs between Na and Ca ; however,
6188-403: The fabrication of superconducting devices such as single-electron transistors , superconducting quantum interference devices ( SQUIDs ) and superconducting qubits . For its application as an electrical insulator in integrated circuits, where the conformal growth of a thin film is a prerequisite and the preferred growth mode is atomic layer deposition , Al 2 O 3 films can be prepared by
6279-745: The formation of ore deposits. They can also catalyze the dissolution of minerals. Prior to the International Mineralogical Association's listing, over 60 biominerals had been discovered, named, and published. These minerals (a sub-set tabulated in Lowenstam (1981) ) are considered minerals proper according to Skinner's (2005) definition. These biominerals are not listed in the International Mineral Association official list of mineral names; however, many of these biomineral representatives are distributed amongst
6370-410: The generic AX 2 formula; these two groups are collectively known as the pyrite and marcasite groups. Polymorphism can extend beyond pure symmetry content. The aluminosilicates are a group of three minerals – kyanite , andalusite , and sillimanite – which share the chemical formula Al 2 SiO 5 . Kyanite is triclinic, while andalusite and sillimanite are both orthorhombic and belong to
6461-438: The hardness of natural and synthetic corundum. Instead, with plasma electrolytic oxidation , the coating is porous only on the surface oxide layer while the lower oxide layers are much more compact than with standard DC anodizing procedures and present a higher crystallinity due to the oxide layers being remelted and densified to obtain α-Al2O3 clusters with much higher coating hardness values circa 2000 Vickers hardness. Alumina
6552-451: The hexaoctahedral point group (isometric family), as they have a similar stoichiometry between their different constituent elements. In contrast, polymorphs are groupings of minerals that share a chemical formula but have a different structure. For example, pyrite and marcasite , both iron sulfides, have the formula FeS 2 ; however, the former is isometric while the latter is orthorhombic. This polymorphism extends to other sulfides with
6643-620: The highlands in 1895 with the first hydro-electric powered smelter opening in 1896 followed by two more, at Kinlochleven in 1909 and Lochaber in 1929. Unsuccessful attempts at bauxite extraction in Northern Ireland forced the company to acquire a controlling interest in Union des Bauxites of Southern France . This established source was supplemented by the acquisition of bauxite rights in British Guiana during World War I followed by more in
6734-461: The material to be a stable or metastable solid at room temperature (25 °C). However, the IMA only requires that the substance be stable enough for its structure and composition to be well-determined. For example, it has recently recognized meridianiite (a naturally occurring hydrate of magnesium sulfate ) as a mineral, even though it is formed and stable only below 2 °C. As of November 2024 , 6,100 mineral species are approved by
6825-499: The material. The insulation can be made in blanket, board, brick and loose fiber forms for various application requirements. It is also used to make spark plug insulators . Using a plasma spray process and mixed with titania , it is coated onto the braking surface of some bicycle rims to provide abrasion and wear resistance. Most ceramic eyes on fishing rods are circular rings made from aluminium oxide. In its finest powdered (white) form, called Diamantine, aluminium oxide
6916-400: The mineral deltalumite. The field of aluminium oxide ceramics has a long history. Aluminium salts were widely used in ancient and medieval alchemy . Several older textbooks cover the history of the field. A 2019 textbook by Andrew Ruys contains a detailed timeline on the history of aluminium oxide from ancient times to the 21st century. Al 2 O 3 is an electrical insulator but has
7007-433: The mineral's structure; for example, the formula of mackinawite is given as (Fe,Ni) 9 S 8 , meaning Fe x Ni 9- x S 8 , where x is a variable number between 0 and 9. Sometimes a mineral with variable composition is split into separate species, more or less arbitrarily, forming a mineral group ; that is the case of the silicates Ca x Mg y Fe 2- x - y SiO 4 ,
7098-489: The most common gemstones. Gem minerals are often present in several varieties, and so one mineral can account for several different gemstones; for example, ruby and sapphire are both corundum , Al 2 O 3 . The first known use of the word "mineral" in the English language ( Middle English ) was the 15th century. The word came from Medieval Latin : minerale , from minera , mine, ore. The word "species" comes from
7189-428: The most encompassing of these being the six crystal families. These families can be described by the relative lengths of the three crystallographic axes, and the angles between them; these relationships correspond to the symmetry operations that define the narrower point groups. They are summarized below; a, b, and c represent the axes, and α, β, γ represent the angle opposite the respective crystallographic axis (e.g. α
7280-402: The olivine series of magnesium-rich forsterite and iron-rich fayalite, and the wolframite series of manganese -rich hübnerite and iron-rich ferberite . Chemical substitution and coordination polyhedra explain this common feature of minerals. In nature, minerals are not pure substances, and are contaminated by whatever other elements are present in the given chemical system. As a result, it
7371-622: The orderly geometric spatial arrangement of atoms in the internal structure of a mineral. This crystal structure is based on regular internal atomic or ionic arrangement that is often expressed in the geometric form that the crystal takes. Even when the mineral grains are too small to see or are irregularly shaped, the underlying crystal structure is always periodic and can be determined by X-ray diffraction. Minerals are typically described by their symmetry content. Crystals are restricted to 32 point groups , which differ by their symmetry. These groups are classified in turn into more broad categories,
7462-563: The point where they can no longer be accommodated in common minerals. Changes in temperature and pressure and composition alter the mineralogy of a rock sample. Changes in composition can be caused by processes such as weathering or metasomatism ( hydrothermal alteration ). Changes in temperature and pressure occur when the host rock undergoes tectonic or magmatic movement into differing physical regimes. Changes in thermodynamic conditions make it favourable for mineral assemblages to react with each other to produce new minerals; as such, it
7553-408: The powdery abrasive mineral aloxite , it is a major component, along with silica , of the cue tip "chalk" used in billiards . Aluminium oxide powder is used in some CD / DVD polishing and scratch-repair kits. Its polishing qualities are also behind its use in toothpaste. It is also used in microdermabrasion , both in the machine process available through dermatologists and estheticians, and as
7644-657: The precious gemstones ruby and sapphire . Al 2 O 3 is used to produce aluminium metal, as an abrasive owing to its hardness , and as a refractory material owing to its high melting point. Corundum is the most common naturally occurring crystalline form of aluminium oxide. Rubies and sapphires are gem-quality forms of corundum, which owe their characteristic colours to trace impurities. Rubies are given their characteristic deep red colour and their laser qualities by traces of chromium . Sapphires come in different colours given by various other impurities, such as iron and titanium. An extremely rare δ form occurs as
7735-447: The presence of repetitive twinning; however, instead of occurring around a rotational axis, polysynthetic twinning occurs along parallel planes, usually on a microscopic scale. Crystal habit refers to the overall shape of crystal. Several terms are used to describe this property. Common habits include acicular, which describes needlelike crystals as in natrolite , bladed, dendritic (tree-pattern, common in native copper ), equant, which
7826-560: The previous definition of a mineral to classify "element or compound, amorphous or crystalline, formed through biogeochemical processes," as a mineral. Recent advances in high-resolution genetics and X-ray absorption spectroscopy are providing revelations on the biogeochemical relations between microorganisms and minerals that may shed new light on this question. For example, the IMA-commissioned "Working Group on Environmental Mineralogy and Geochemistry " deals with minerals in
7917-489: The principal ore of aluminium . A mixture of the minerals comprise bauxite ore, including gibbsite (Al(OH) 3 ), boehmite (γ-AlO(OH)), and diaspore (α-AlO(OH)), along with impurities of iron oxides and hydroxides, quartz and clay minerals . Bauxites are found in laterites . Bauxite is typically purified using the Bayer process : Except for SiO 2 , the other components of bauxite do not dissolve in base. Upon filtering
8008-485: The second aluminium is in six-fold coordination; its chemical formula can be expressed as Al Al SiO 5 , to reflect its crystal structure. Andalusite has the second aluminium in five-fold coordination (Al Al SiO 5 ) and sillimanite has it in four-fold coordination (Al Al SiO 5 ). Differences in crystal structure and chemistry greatly influence other physical properties of the mineral. The carbon allotropes diamond and graphite have vastly different properties; diamond
8099-439: The twinning is controlled by the mineral's symmetry. As a result, there are several types of twins, including contact twins, reticulated twins, geniculated twins, penetration twins, cyclic twins, and polysynthetic twins. Contact, or simple twins, consist of two crystals joined at a plane; this type of twinning is common in spinel. Reticulated twins, common in rutile, are interlocking crystals resembling netting. Geniculated twins have
8190-468: The two dominant systems are the Dana classification and the Strunz classification. Silicate minerals comprise approximately 90% of the Earth's crust . Other important mineral groups include the native elements , sulfides , oxides , halides , carbonates , sulfates , and phosphates . The International Mineralogical Association has established the following requirements for a substance to be considered
8281-437: The year of the site's 100th anniversary of producing aluminium Dolgarrog was to close. BACo also produced bus bodies, on Daimler Fleetline and Leyland Fleetline chassis for Kowloon Motor Bus as well as Leyland Atlantean chassis for Singapore Bus Services . The chairmen of British Aluminium have been: Alumina Aluminium oxide (or aluminium(III) oxide ) is a chemical compound of aluminium and oxygen with
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