Magnetite

This article is about the mineral magnetite as found in natural deposits. For other uses, see Iron(II,III) oxide.

Not to be confused with magnesite or manganite.

Magnetite
Magnetite from Bolivia
General
Category	Oxide minerals Spinel group Spinel structural group
Formula	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
Density	5 g/cm3
Solubility	Dissolves slowly in hydrochloric acid
References
Major varieties
Lodestone	Magnetic with definite north and south poles

Magnetite is one of the very few minerals that is ferrimagnetic; it is attracted by a magnet as shown here

Unit cell of magnetite. The gray spheres are oxygen, green are divalent iron, blue are trivalent iron. Also shown are an iron atom in an octahedral space (light blue) and another in a tetrahedral space (gray).

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 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.