Magnetite
| Magnetite | |
|---|---|
Magnetite from Bolivia
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| General | |
| Category |
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Formula (repeating unit) |
iron(II,III) oxide, Fe2+Fe3+2O4 |
| Strunz classification | 4.BB.05 |
| Crystal system | Isometric |
| Crystal class | Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m) |
| Space group | Fd3m |
| Unit cell | a = 8.397 Å; Z = 8 |
| Identification | |
| Color | Black, gray with brownish tint in reflected sun |
| Crystal habit | Octahedral, fine granular to massive |
| Twinning | On {Ill} as both twin and composition plane, the spinel law, as contact twins |
| Cleavage | Indistinct, parting on {Ill}, very good |
| Fracture | Uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 5.5–6.5 |
| Luster | Metallic |
| Streak | Black |
| Diaphaneity | Opaque |
| Specific gravity | 5.17–5.18 |
| Solubility | Dissolves slowly in hydrochloric acid |
| References | |
| Major varieties | |
| Lodestone | Magnetic with definite north and south poles |
Magnetite is a mineral and one of the main iron ores. With the chemical formula Fe3O4, it is one of the oxides of iron. Magnetite is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. 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, which is how ancient peoples first discovered the property of magnetism. Today it is mined as iron ore.
Small grains of magnetite occur in almost 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(II,III) oxide and the common chemical name is ferrous-ferric oxide.
In addition to igneous rocks, magnetite also occurs in sedimentary rocks, including banded iron formations and in lake and marine sediments as both detrital grains and as magnetofossils. Magnetite nanoparticles are also thought to form in soils, where they probably oxidize rapidly to maghemite.
Magnetite has an inverse spinel crystal structure. As a member of the spinel group, it can form solid solutions with similarly structured minerals, including ulvospinel (Fe2TiO4), hercynite (FeAl2O4) and chromite (FeCr2O4). Titanomagnetite, also 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.
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Wikipedia