Magnetite
Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With the exception of extremely rare native iron deposits, 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.
| Magnetite | |
|---|---|
Magnetite from Bolivia | |
| General | |
| Category |
|
| Formula (repeating unit) | iron(II,III) oxide, Fe2+Fe3+2O4 |
| IMA symbol | Mag |
| Strunz classification | 4.BB.05 |
| Crystal system | Isometric |
| Crystal class | Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m) |
| Space group | Fd3m (no. 227) |
| 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 black or brownish-black with a metallic luster, has a Mohs hardness of 5–6 and leaves a black streak. Small grains of magnetite are very common in igneous and metamorphic rocks.
The chemical IUPAC name is iron(II,III) oxide and the common chemical name is ferrous-ferric oxide.