Redox is a chemical reaction in which the oxidation states of atoms are changed. Any such reaction involves both a reduction process and a complementary oxidation process, two key concepts involved with electron transfer processes. Redox reactions include all chemical reactions; the chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. It can be explained in simple terms: Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion. Reduction is a decrease in oxidation state by a molecule, atom, or ion; as an example, during the combustion of wood, oxygen from the air is reduced, gaining electrons from carbon, oxidized. Although oxidation reactions are associated with the formation of oxides from oxygen molecules, oxygen is not included in such reactions, as other chemical species can serve the same function; the reaction can occur slowly, as with the formation of rust, or more in the case of fire.
There are simple redox processes, such as the oxidation of carbon to yield carbon dioxide or the reduction of carbon by hydrogen to yield methane, more complex processes such as the oxidation of glucose in the human body. "Redox" is a portmanteau of the words "reduction" and "oxidation". The word oxidation implied reaction with oxygen to form an oxide, since dioxygen was the first recognized oxidizing agent; the term was expanded to encompass oxygen-like substances that accomplished parallel chemical reactions. The meaning was generalized to include all processes involving loss of electrons; the word reduction referred to the loss in weight upon heating a metallic ore such as a metal oxide to extract the metal. In other words, ore was "reduced" to metal. Antoine Lavoisier showed. Scientists realized that the metal atom gains electrons in this process; the meaning of reduction became generalized to include all processes involving a gain of electrons. Though "reduction" seems counter-intuitive when speaking of the gain of electrons, it might help to think of reduction as the loss of oxygen, its historical meaning.
Since electrons are negatively charged, it is helpful to think of this as reduction in electrical charge. The electrochemist John Bockris has used the words electronation and deelectronation to describe reduction and oxidation processes when they occur at electrodes; these words are analogous to protonation and deprotonation, but they have not been adopted by chemists worldwide. The term "hydrogenation" could be used instead of reduction, since hydrogen is the reducing agent in a large number of reactions in organic chemistry and biochemistry. But, unlike oxidation, generalized beyond its root element, hydrogenation has maintained its specific connection to reactions that add hydrogen to another substance; the word "redox" was first used in 1928. The processes of oxidation and reduction occur and cannot happen independently of one another, similar to the acid–base reaction; the oxidation alone and the reduction alone are each called a half-reaction, because two half-reactions always occur together to form a whole reaction.
When writing half-reactions, the gained or lost electrons are included explicitly in order that the half-reaction be balanced with respect to electric charge. Though sufficient for many purposes, these general descriptions are not correct. Although oxidation and reduction properly refer to a change in oxidation state — the actual transfer of electrons may never occur; the oxidation state of an atom is the fictitious charge that an atom would have if all bonds between atoms of different elements were 100% ionic. Thus, oxidation is best defined as an increase in oxidation state, reduction as a decrease in oxidation state. In practice, the transfer of electrons will always cause a change in oxidation state, but there are many reactions that are classed as "redox" though no electron transfer occurs. In redox processes, the reductant transfers electrons to the oxidant. Thus, in the reaction, the reductant or reducing agent loses electrons and is oxidized, the oxidant or oxidizing agent gains electrons and is reduced.
The pair of an oxidizing and reducing agent that are involved in a particular reaction is called a redox pair. A redox couple is a reducing species and its corresponding oxidizing form, e.g. Fe2+/Fe3+ Substances that have the ability to oxidize other substances are said to be oxidative or oxidizing and are known as oxidizing agents, oxidants, or oxidizers; that is, the oxidant removes electrons from another substance, is thus itself reduced. And, because it "accepts" electrons, the oxidizing agent is called an electron acceptor. Oxygen is the quintessential oxidizer. Oxidants are chemical substances with elements in high oxidation states, or else electronegative elements that can gain extra electrons by oxidizing another substance. Substances that have the ability to reduce other substances are said to be reductive or reducing and are known as
The flash point of a volatile material is the lowest temperature at which vapours of the material will ignite, when given an ignition source. The flash point is sometimes confused with the autoignition temperature, the temperature that results in spontaneous autoignition; the fire point is the lowest temperature at which vapors of the material will keep burning after the ignition source is removed. The fire point is higher than the flash point, because at the flash point more vapor may not be produced enough to sustain combustion. Neither flash point nor fire point depends directly on the ignition source temperature, but ignition source temperature is far higher than either the flash or fire point; the flash point is a descriptive characteristic, used to distinguish between flammable fuels, such as petrol, combustible fuels, such as diesel. It is used to characterize the fire hazards of fuels. Fuels which have a flash point less than 37.8 °C are called flammable, whereas fuels having a flash point above that temperature are called combustible.
All liquids have a specific vapor pressure, a function of that liquid's temperature and is subject to Boyle's Law. As temperature increases, vapor pressure increases; as vapor pressure increases, the concentration of vapor of a flammable or combustible liquid in the air increases. Hence, temperature determines the concentration of vapor of the flammable liquid in the air. A certain concentration of a flammable or combustible vapor is necessary to sustain combustion in air, the lower flammable limit, that concentration is different and is specific to each flammable or combustible liquid; the flash point is the lowest temperature at which there will be enough flammable vapor to induce ignition when an ignition source is applied There are two basic types of flash point measurement: open cup and closed cup. In open cup devices, the sample is contained in an open cup, heated and, at intervals, a flame brought over the surface; the measured flash point will vary with the height of the flame above the liquid surface and, at sufficient height, the measured flash point temperature will coincide with the fire point.
The best-known example is the Cleveland open cup. There are two types of closed cup testers: non-equilibrial, such as Pensky-Martens, where the vapours above the liquid are not in temperature equilibrium with the liquid, equilibrial, such as Small Scale, where the vapours are deemed to be in temperature equilibrium with the liquid. In both these types, the cups are sealed with a lid through which the ignition source can be introduced. Closed cup testers give lower values for the flash point than open cup and are a better approximation to the temperature at which the vapour pressure reaches the lower flammable limit; the flash point is an empirical measurement rather than a fundamental physical parameter. The measured value will vary with equipment and test protocol variations, including temperature ramp rate, time allowed for the sample to equilibrate, sample volume and whether the sample is stirred. Methods for determining the flash point of a liquid are specified in many standards. For example, testing by the Pensky-Martens closed cup method is detailed in ASTM D93, IP34, ISO 2719, DIN 51758, JIS K2265 and AFNOR M07-019.
Determination of flash point by the Small Scale closed cup method is detailed in ASTM D3828 and D3278, EN ISO 3679 and 3680, IP 523 and 524. CEN/TR 15138 Guide to Flash Point Testing and ISO TR 29662 Guidance for Flash Point Testing cover the key aspects of flash point testing. Gasoline is a fuel used in a spark-ignition engine; the fuel is mixed with air within its flammable limits and heated by compression and subject to Boyle's Law above its flash point ignited by the spark plug. To ignite, the fuel must have a low flash point, but in order to avoid preignition caused by residual heat in a hot combustion chamber, the fuel must have a high autoignition temperature. Diesel fuel flash points vary between 52 and 96 °C. Diesel is suitable for use in a compression-ignition engine. Air is compressed until it has been heated above the autoignition temperature of the fuel, injected as a high-pressure spray, keeping the fuel–air mix within flammable limits. In a diesel-fueled engine, there is no ignition source.
Diesel fuel must have a high flash point and a low autoignition temperature. Jet fuel flash points vary with the composition of the fuel. Both Jet A and Jet A-1 have flash points between 38 and 66 °C, close to that of off-the-shelf kerosene, yet both Jet B and JP-4 have flash points between −23 and −1 °C. Flash points of substances are measured according to standard test methods described and defined in a 1938 publication by T. L. Ainsley of South Shields entitled "Sea Transport of Petroleum"; the test methodology defines the apparatus required to carry out the measurement, key test parameters, the procedure for the operator or automated apparatus to follow, the precision of the test method. Standard test methods are written and controlled by a number of national and international committees and organizations; the three main bodies are the CEN / ISO Joint Working Group on Flash Point, ASTM D02.8B Flammability Section and the Energy Institute's TMS SC-B-4 Flammability Panel. Autoignition temperature Fire point Safety data sheet
CRC Handbook of Chemistry and Physics
The CRC Handbook of Chemistry and Physics is a comprehensive one-volume reference resource for science research in its 99th edition. It is sometimes nicknamed the "Rubber Bible" or the "Rubber Book", as CRC stood for "Chemical Rubber Company"; as late as the 1962–1963 edition the Handbook contained myriad information for every branch of science and engineering. Sections in that edition include: Mathematics and Physical Constants, Chemical Tables, Properties of Matter, Heat and Barometric Tables, Sound and Units, Miscellaneous. Earlier editions included sections such as "Antidotes of Poisons", "Rules for Naming Organic Compounds", "Surface Tension of Fused Salts", "Percent Composition of Anti-Freeze Solutions", "Spark-gap Voltages", "Greek Alphabet", "Musical Scales", "Pigments and Dyes", "Comparison of Tons and Pounds", "Twist Drill and Steel Wire Gauges" and "Properties of the Earth's Atmosphere at Elevations up to 160 Kilometers". Editions focus exclusively on chemistry and physics topics and eliminated much of the more "common" information.
22nd Edition – 44th Edition Section A: Mathematical Tables Section B: Properties and Physical Constants Section C: General Chemical Tables/Specific Gravity and Properties of Matter Section D: Heat and Hygrometry/Sound/Electricity and Magnetism/Light Section E: Quantities and Units/Miscellaneous Index 45th Edition – 70th Edition Section A: Mathematical Tables Section B: Elements and Inorganic Compounds Section C: Organic Compounds Section D: General Chemical Section E: General Physical Constants Section F: Miscellaneous Index 71st Edition – Current edition Section 1: Basic Constants and Conversion Factors Section 2: Symbols and Nomenclature Section 3: Physical Constants of Organic Compounds Section 4: Properties of the Elements and Inorganic Compounds Section 5: Thermochemistry and Kinetics Section 6: Fluid Properties Section 7: Biochemistry Section 8: Analytical Chemistry Section 9: Molecular Structure and Spectroscopy Section 10: Atomic and Optical Physics Section 11: Nuclear and Particle Physics Section 12: Properties of Solids Section 13: Polymer Properties Section 14: Geophysics and Acoustics Section 15: Practical Laboratory Data Section 16: Health and Safety Information Appendix A: Mathematical Tables Appendix B: CAS Registry Numbers and Molecular Formulas of Inorganic Substances Appendix B: Sources of Physical and Chemical Data IndexIn addition to an extensive line of engineering handbooks and references and textbooks across all scientific disciplines, CRC is today known as a leading publisher of books related to forensic sciences, forensic pathology and police sciences.
CORDIC PDF copy of the 8th edition, published in 1920 Handbook of Chemistry and Physics online Tables Relocated or Removed from CRC Handbook of Chemistry and Physics, 71st through 87th Editions
The density, or more the volumetric mass density, of a substance is its mass per unit volume. The symbol most used for density is ρ, although the Latin letter D can be used. Mathematically, density is defined as mass divided by volume: ρ = m V where ρ is the density, m is the mass, V is the volume. In some cases, density is loosely defined as its weight per unit volume, although this is scientifically inaccurate – this quantity is more called specific weight. For a pure substance the density has the same numerical value as its mass concentration. Different materials have different densities, density may be relevant to buoyancy and packaging. Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. To simplify comparisons of density across different systems of units, it is sometimes replaced by the dimensionless quantity "relative density" or "specific gravity", i.e. the ratio of the density of the material to that of a standard material water.
Thus a relative density less than one means. The density of a material varies with pressure; this variation is small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object and thus increases its density. Increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a fluid results in convection of the heat from the bottom to the top, due to the decrease in the density of the heated fluid; this causes it to rise relative to more dense unheated material. The reciprocal of the density of a substance is called its specific volume, a term sometimes used in thermodynamics. Density is an intensive property in that increasing the amount of a substance does not increase its density. In a well-known but apocryphal tale, Archimedes was given the task of determining whether King Hiero's goldsmith was embezzling gold during the manufacture of a golden wreath dedicated to the gods and replacing it with another, cheaper alloy.
Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated and compared with the mass. Baffled, Archimedes is said to have taken an immersion bath and observed from the rise of the water upon entering that he could calculate the volume of the gold wreath through the displacement of the water. Upon this discovery, he leapt from his bath and ran naked through the streets shouting, "Eureka! Eureka!". As a result, the term "eureka" entered common parlance and is used today to indicate a moment of enlightenment; the story first appeared in written form in Vitruvius' books of architecture, two centuries after it took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time. From the equation for density, mass density has units of mass divided by volume; as there are many units of mass and volume covering many different magnitudes there are a large number of units for mass density in use.
The SI unit of kilogram per cubic metre and the cgs unit of gram per cubic centimetre are the most used units for density. One g/cm3 is equal to one thousand kg/m3. One cubic centimetre is equal to one millilitre. In industry, other larger or smaller units of mass and or volume are more practical and US customary units may be used. See below for a list of some of the most common units of density. A number of techniques as well as standards exist for the measurement of density of materials; such techniques include the use of a hydrometer, Hydrostatic balance, immersed body method, air comparison pycnometer, oscillating densitometer, as well as pour and tap. However, each individual method or technique measures different types of density, therefore it is necessary to have an understanding of the type of density being measured as well as the type of material in question; the density at all points of a homogeneous object equals its total mass divided by its total volume. The mass is measured with a scale or balance.
To determine the density of a liquid or a gas, a hydrometer, a dasymeter or a Coriolis flow meter may be used, respectively. Hydrostatic weighing uses the displacement of water due to a submerged object to determine the density of the object. If the body is not homogeneous its density varies between different regions of the object. In that case the density around any given location is determined by calculating the density of a small volume around that location. In the limit of an infinitesimal volume the density of an inhomogeneous object at a point becomes: ρ = d m / d V, where d V is an elementary volume at position r; the mass of the body t
Iron pentacarbonyl known as iron carbonyl, is the compound with formula Fe5. Under standard conditions Fe5 is a straw-colored liquid with a pungent odour. Older samples appear darker; this compound is a common precursor to diverse iron compounds, including many that are useful in small scale organic synthesis. Iron pentacarbonyl is a homoleptic metal carbonyl, where carbon monoxide is the only ligand complexed with a metal. Other examples include octahedral Cr6 and tetrahedral Ni4. Most metal carbonyls have 18 valence electrons, Fe5 fits this pattern with 8 valence electrons on Fe and five pairs of electrons provided by the CO ligands. Reflecting its symmetrical structure and charge neutrality, Fe5 is volatile. Fe5 adopts a trigonal bipyramidal structure with the Fe atom surrounded by five CO ligands: three in equatorial positions and two axially bound; the Fe -- C -- O. Fe5 exhibits a low rate of interchange between the axial and equatorial CO groups via the Berry mechanism, it is characterized by two intense νCO bands in the IR spectrum at 2034 and 2014 cm-1.
Fe5 is produced by the reaction of fine iron particles with carbon monoxide. The compound was described in a journal by Mond and Langer in 1891 as "a somewhat viscous liquid of a pale-yellow colour." Samples were prepared by treatment of finely divided, oxide-free iron powder with carbon monoxide at room temperature. Industrial synthesis of the compound requires high temperatures and pressures as well as special, chemically resistant equipment. Preparation of the compound at the laboratory scale avoids these complications by using an iodide intermediate: FeI2 + 4 CO → Fe4I2 5 Fe4I2 + 10 Cu → 10 CuI + 4 Fe5 + FeFe5 is sensitive to light. Photodissociation of Fe5 produces Fe29, a yellow-orange solid described by Mond; when heated, Fe5 converts to small amounts of a green solid. Simple thermolysis, however, is not a useful synthesis, each iron carbonyl complex exhibits distinct reactivity; the industrial production of this compound is somewhat similar to the Mond process in that the metal is treated with carbon monoxide to give a volatile gas.
In the case of iron pentacarbonyl, the reaction is more sluggish. It is necessary to use iron sponge as the starting material, harsher reaction conditions of 5–30 MPa of carbon monoxide and 150–200 °C. Similar to the Mond process, sulfur acts as a catalyst; the crude iron pentacarbonyl is purified by distillation. Ullmann's Encyclopedia of Industrial Chemistry reports that there are only three plants manufacturing pentacarbonyliron. Most iron pentacarbonyl produced is decomposed on site to give pure carbonyl iron in analogy to carbonyl nickel; some iron pentacarbonyl is burned to give pure iron oxide. Other uses of pentacarbonyliron are small in comparison. Purified iron pentacarbonyl can be decomposed to produce carbonyl iron, a high-purity preparation of iron metal. Many compounds are derived from Fe5 by substitution of CO by Lewis bases, L, to give derivatives Fe5−xLx. Common Lewis bases include isocyanides, tertiary phosphines and arsines, alkenes; these ligands displace only one or two CO ligands, but certain acceptor ligands such as PF3 and isocyanides can proceed to tetra- and pentasubstitution.
These reactions are induced with a catalyst or light. Illustrative is the synthesis of the bis complex Fe32; this transformation can be accomplished photochemically, but it is induced by the addition of NaOH or NaBH4. The catalyst attacks a CO ligand; the electrophilicity of Fe4L is less than that of Fe5, so the nucleophilic catalyst and attacks another molecule of Fe5. Most metal carbonyls can be halogenated. Thus, treatment of Fe5 with halogens gives the ferrous halides Fe4X2 for Br, Cl; these species, upon heating lose CO to give the ferrous halides, such as iron chloride. Reduction of Fe5 with Na gives Na2Fe4, "tetracarbonylferrate" called Collman's reagent; the dianion is isoelectronic with Ni4 but nucleophilic. Fe5 is not protonated, but it is attacked by hydroxide. Treatment of Fe5 with aqueous base produces −, via the Metallacarboxylate intermediate; the oxidation of this monoanion gives triiron dodecarbonyl, Fe312. Acidification of solutions of − gives iron tetracarbonyl hydride, H2Fe4, the first metal hydride reported.
Dienes react with Fe5 to give Fe3. Many dienes undergo this reaction, notably 1,3-butadiene. One of the more significant derivatives is cyclobutadieneiron tricarbonyl Fe3, where C4H4 is the otherwise unstable cyclobutadiene. Receiving the greatest attention are complexes of the cyclohexadienes, the parent organic 1,4-dienes being available through the Birch reductions. 1,4-Dienes isomerize to the 1,3-dienes upon complexation. Fe5 reacts in dicyclopentadiene to form cyclopentadienyliron dicarbonyl dimer; this compound, called "Fp dimer" can be considered a hybrid of ferrocene and Fe5, although in terms of its reactivity, it resembles neither. In Europe, iron pentacarbonyl was once used as an anti-knock agent in petrol in place of tetraethyllead. Two more modern alternative fuel additives are ferrocene and methylcyclopentadienyl manganese tricarbonyl. Fe5 is used
Western Australia is a state occupying the entire western third of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, South Australia to the south-east. Western Australia is Australia's largest state, with a total land area of 2,529,875 square kilometres, the second-largest country subdivision in the world, surpassed only by Russia's Sakha Republic; the state has about 2.6 million inhabitants – around 11 percent of the national total – of whom the vast majority live in the south-west corner, 79 per cent of the population living in the Perth area, leaving the remainder of the state sparsely populated. The first European visitor to Western Australia was the Dutch explorer Dirk Hartog, who visited the Western Australian coast in 1616; the first European settlement of Western Australia occurred following the landing by Major Edmund Lockyer on 26 December 1826 of an expedition on behalf of the New South Wales colonial government.
He established a convict-supported military garrison at King George III Sound, at present-day Albany, on 21 January 1827 formally took possession of the western third of the continent for the British Crown. This was followed by the establishment of the Swan River Colony in 1829, including the site of the present-day capital, Perth. York was the first inland settlement in Western Australia. Situated 97 kilometres east of Perth, it was settled on 16 September 1831. Western Australia achieved responsible government in 1890 and federated with the other British colonies in Australia in 1901. Today, its economy relies on mining, agriculture and tourism; the state produces 46 per cent of Australia's exports. Western Australia is the second-largest iron ore producer in the world. Western Australia is bounded to the east by longitude 129°E, the meridian 129 degrees east of Greenwich, which defines the border with South Australia and the Northern Territory, bounded by the Indian Ocean to the west and north.
The International Hydrographic Organization designates the body of water south of the continent as part of the Indian Ocean. The total length of the state's eastern border is 1,862 km. There are 20,781 km including 7,892 km of island coastline; the total land area occupied by the state is 2.5 million km2. The bulk of Western Australia consists of the old Yilgarn craton and Pilbara craton which merged with the Deccan Plateau of India and the Karoo and Zimbabwe cratons of Southern Africa, in the Archean Eon to form Ur, one of the oldest supercontinents on Earth. In May 2017, evidence of the earliest known life on land may have been found in 3.48-billion-year-old geyserite and other related mineral deposits uncovered in the Pilbara craton. Because the only mountain-building since has been of the Stirling Range with the rifting from Antarctica, the land is eroded and ancient, with no part of the state above 1,245 metres AHD. Most of the state is a low plateau with an average elevation of about 400 metres low relief, no surface runoff.
This descends sharply to the coastal plains, in some cases forming a sharp escarpment. The extreme age of the landscape has meant that the soils are remarkably infertile and laterised. Soils derived from granitic bedrock contain an order of magnitude less available phosphorus and only half as much nitrogen as soils in comparable climates in other continents. Soils derived from extensive sandplains or ironstone are less fertile, nearly devoid of soluble phosphate and deficient in zinc, copper and sometimes potassium and calcium; the infertility of most of the soils has required heavy application by farmers of fertilizers. These have resulted in damage to bacterial populations; the grazing and use of hoofed mammals and heavy machinery through the years have resulted in compaction of soils and great damage to the fragile soils. Large-scale land clearing for agriculture has damaged habitats for native fauna; as a result, the South West region of the state has a higher concentration of rare, threatened or endangered flora and fauna than many areas of Australia, making it one of the world's biodiversity "hot spots".
Large areas of the state's wheatbelt region have problems with dryland salinity and the loss of fresh water. The southwest coastal area has a Mediterranean climate, it was heavily forested, including large stands of karri, one of the tallest trees in the world. This agricultural region is one of the nine most bio-diverse terrestrial habitats, with a higher proportion of endemic species than most other equivalent regions. Thanks to the offshore Leeuwin Current, the area is one of the top six regions for marine biodiversity and contains the most southerly coral reefs in the world. Average annual rainfall varies from 300 millimetres at the edge of the Wheatbelt region to 1,400 millimetres in the wettest areas near Northcliffe, but from November to March, evaporation exceeds rainfall, it is very dry. Plants are adapted to this as well as the extreme poverty of all soils; the central two-thirds of the state is sparsely inhabited. The only significant economic activity is mining. Annual rainfall averages less than 300 millimetres, most of which occurs in sporadic torrential falls related to cyclone events in summer.
An exception to this is
Magnetite is a rock mineral and one of the main iron ores, with the chemical formula Fe3O4. It is one of the oxides of iron, is ferrimagnetic, it is the most magnetic of all the naturally-occurring minerals on Earth. Naturally-magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, how ancient peoples first discovered the property of magnetism. Today it is mined as iron ore. Small grains of magnetite occur in all igneous and metamorphic rocks. Magnetite is black or brownish-black with a metallic luster, has a Mohs hardness of 5–6 and leaves a black streak; the chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. In addition to igneous rocks, magnetite occurs in sedimentary rocks, including banded iron formations and in lake and marine sediments as both detrital grains and as magnetofossils. Magnetite nanoparticles are thought to form in soils, where they oxidize to maghemite; the chemical composition of magnetite is Fe2+Fe23+O42−. The main details of its structure were established in 1915.
It was one of the first crystal structures to be obtained using X-ray diffraction. The structure is inverse spinel, with O2− ions forming a face centered cubic lattice and iron cations occupying interstitial sites. Half of the Fe3+ cations occupy tetrahedral sites while the other half, along with Fe2+ cations, occupy octahedral sites; the unit cell consists of 32 O2− ions and unit cell length is a = 0.839 nm. Magnetite contains both ferrous and ferric iron, requiring environments containing intermediate levels of oxygen availability to form. Magnetite differs from most other iron oxides in that it contains both trivalent iron; as a member of the spinel group, magnetite can form solid solutions with structured minerals, including ulvospinel and chromite. Titanomagnetite known as titaniferous magnetite, is a solid solution between magnetite and ulvospinel that crystallizes in many mafic igneous rocks. Titanomagnetite may undergo oxyexsolution during cooling, resulting in ingrowths of magnetite and ilmenite.
Natural and synthetic magnetite occurs most as octahedral crystals bounded by planes and as rhombic-dodecahedra. Twinning occurs on the plane. Hydrothermal synthesis produce single octahedral crystals which can be as large as 10mm across. In the presence of mineralizers such as 0.1M HI or 2M NH4Cl and at 0.207 MPa at 416-800 °C, magnetite grew as crystals whose shapes were a combination of rhombic-dodechahedra forms. The crystals were more rounded than usual; the appearance of higher forms was considered as a result from a decrease in the surface energies caused by the lower surface to volume ratio in the rounded crystals. Magnetite has been important in understanding the conditions. Magnetite reacts with oxygen to produce hematite, the mineral pair forms a buffer that can control oxygen fugacity. Igneous rocks contain solid solutions of both titanomagnetite and hemoilmenite or titanohematite. Compositions of the mineral pairs are used to calculate how oxidizing was the magma: a range of oxidizing conditions are found in magmas and the oxidation state helps to determine how the magmas might evolve by fractional crystallization.
Magnetite is produced from peridotites and dunites by serpentinization. Lodestones were used as an early form of magnetic compass. Magnetite carries the dominant magnetic signature in rocks, so it has been a critical tool in paleomagnetism, a science important in understanding plate tectonics and as historic data for magnetohydrodynamics and other scientific fields; the relationships between magnetite and other iron oxide minerals such as ilmenite and ulvospinel have been much studied. At low temperatures, magnetite undergoes a crystal structure phase transition from a monoclinic structure to a cubic structure known as the Verwey transition. Optical studies show that this metal to insulator transition is sharp and occurs around 120 K; the Verwey transition is dependent on grain size, domain state and the iron-oxygen stoichiometry. An isotropic point occurs near the Verwey transition around 130 K, at which point the sign of the magnetocrystalline anisotropy constant changes from positive to negative.
The Curie temperature of magnetite is 858 K. If magnetite is in a large enough quantity it can be found in aeromagnetic surveys using a magnetometer which measures magnetic intensities. Magnetite is sometimes found in large quantities in beach sand; such black sands are found in various places, such as Lung Kwu Tan of Hong Kong. The magnetite, eroded from rocks, is carried to the beach by rivers and concentrated by wave action and currents. Huge deposits have been found in banded iron formations; these sedimentary rocks have been used to infer changes in the oxygen content of the atmosphere of the Earth. Remote sensing has the potential to be a big part in locating magnetite sands as small amounts of magnetite in sand can drastically alter the sands albedo, the amount of electromagnetic radiation the sand will reflect; the darker magnetite will lower the sands albedo compared to sands. Large deposits of magnetite are found in the Atacama region of Chile.