magnetite


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magnetite

(măg`nətīt), lustrous black, magnetic mineral, Fe3O4. It occurs in crystals of the cubic system, in masses, and as a loose sand. It is one of the important ores of iron (magnetic iron ore) and is a common constituent of igneous and metamorphic rocks. It is found in Norway, Sweden, the Urals, and various parts of the United States. A variety of magnetite, lodestone (or loadstone) exhibits polarity and is especially interesting for its natural magnetism; Magnet Cove, Ark., became famous as a source.

Magnetite

 

a mineral, a complex oxide of composition FeO.Fe2O3, containing 31 percent FeO and 69 percent Fe2O3 (a total of 72.4 percent Fe), and frequent admixtures of MgO, Cr2O3, Al2O3, MnO, and ZnO. Magnetite is a ferrite and has the inverse spinel structure. It crystallizes in the isometric system a0 = 8.3963 Å, generally forming octahedral, more rarely dodecahedral, crystals and granular aggregates. Magnetite rarely occurs in the form of colloform aggregates.

Synthesized magnetite is widely used in industry. It is usually obtained by synthesis in the solid phase following the combined roasting of pressed FeO and Fe2O3 powders at temperatures of 1000-1400°C

Magnetite is brittle with an uneven fracture; it exhibits no cleavage. It has a hardness of 5.5-6 on Mohs’ scale and a density of 4,800-5,300 kg/m3. A black mineral, it is opaque, and has a semimetallic, sometimes dull, luster. A good conductor of electricity, magnetite is classified as a ferrimagnet owing to its magnetic properties. Its magnetization is determined by the difference in magnetic moments of the mineral’s two magnetic sublattices: (1) composed of Fe2+ and Fe3+ ions, located at the octahedral points, and (2) composed of Fe3+ ions, located at the tetrahedral points. At room temperature, the saturation magnetization of magnetite is Js = 4.8 ×102 tesla (480 gauss). The coercive force Hc of natural magnetite depends on the admixture content, while that of synthesized magnetite is conditioned by the method used to obtain the magnetite. In magnetite powders, Hc increases with decreasing particle size [in fine powders, Hc ~ 12-16 kA/m (150-200 oersteds)]. Magnetodielectrics are manufactured from these powders. At temperatures above 550-600°C (above the Curie point), magnetite becomes paramagnetic. Magnetite has a melting point of 1591-1597°C. Oxidation of magnetite leads to hematite (martite); muschketowite is the pseudomorph of magnetite after crystalline hematite. Varieties of magnetite are distinguished as a result of increased content of isomorphic admixtures: magnesioferrite, manganmagnetite, vanadomagnetite, chromian magnetite, and aluminian magnetite. Magnetite is included in the titanomagnetite category when found in close penetration with ilmenite and other titanium minerals (decomposition structure of solid solutions).

Magnetite occurs in deposits of various origins; however, the main industrial deposits are located in complex magmatic, con-tact metasomatic, or regional metamorphic formations. Magnetite frequently occurs in magmatic, sedimentary, and metamorphic rocks as an accessory mineral.

V. M. GRIGOR’EV

magnetite

[′mag·nə‚tīt]
(mineralogy)
An opaque iron-black and streak-black isometric mineral and member of the spinel structure type, usually occurring in octahedrals or in granular to massive form; hardness is 6 on Mohs scale, and specific gravity is 5.20. Also known as magnetic iron ore; octahedral iron ore.

magnetite

A natural black oxide of iron, containing from about 65 to 72% iron and sometimes a small amount of nickel and titanium; used as an aggregate in high-density concrete.

magnetite

a black magnetic mineral, found in igneous and metamorphic rocks and as a separate deposit. It is a source of iron. Composition: iron oxide. Formula: Fe3O4. Crystal structure: cubic
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The spherical magnetite nanoparticles were about 150 nanometers in diameter.
Single-Domain (SD) Size and Restricted Anisotropic Width/Length Ratios Both size and crystal morphology determine how well magnetite crystals can work as discrete magnets (Thomas-Keprta et al.
A small but crystallographically unique occurrence of magnetite crystals was encountered in the Fowler orebody in 1991.
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Titration curve data for bentonite, magnetite and their mixtures and sorption experimental data (sorption dependencies on pH) for Cs and Sr from granitic water were acquired.
That knowledge, in turn, permits the age of other murals to be deduced from the alignment of their magnetite particles.
We previously had utilized thermomagnetic analysis of carbonaceous chondrites to establish the presence of magnetite ([Fe.
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The minerals include K-feldspar (microcline), quartz, plagioclase, biotite, aegirine-augite, hornblende, riebeckite, titanite, epidote, apatite, zircon and magnetite.
The Mines and Geosciences Bureau (MGB) in the Ilocos region has reaffirmed the decision that blacksand extraction in four villages here was illegal, saying it would confiscate the stockpile of magnetite sand that a government-contracted firm had removed from 2011 to 2013.
AkzoNobel reported that one of its senior managers presented a paper at the X CIS Congress of Mineral Processing Engineers on optimizing reverse flotation of iron ore, especially magnetite ores.