Iron(II,III) sulfide

Iron(II,III) sulfide

Names
Other names Ferrous-ferric sulfide, greigite
Properties
Chemical formula	FeS·Fe2S3
Molar mass	295.805
Appearance	Bluish-black, pinkish
Density	4.049 g/cm3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Iron(II,III) sulfide is a blue-black (sometimes pinkish) chemical compound of iron and sulfur with formula Fe₃S₄ or FeS·Fe₂S₃, which is much similar to iron(II,III) oxide. It occurs naturally as the sulfide mineral greigite and is magnetic. It is a bio-mineral produced by and found in magnetotactic bacteria. It is a mixed valence compound, featuring both Fe²⁺ and Fe³⁺ centers, in 1:2 ratio.

Crystal structure

The crystallographic unit cell is cubic, with space group Fd3m. The S anions form a cubic close-packed lattice, and the Fe cations occupy both tetrahedral and octahedral sites.

Crystal structure of iron(II,III) sulfide projected along the [110] direction
Emphasis on the SFe4 tetrahedra. Emphasis on the SFe4 tetrahedra.  Emphasis on the FeS4 tetrahedra Emphasis on the FeS4 tetrahedra  Emphasis on the FeS6 octahedra Emphasis on the FeS6 octahedra

Magnetic and electronic properties

Like the related oxide magnetite (Fe₃O₄), iron(II,III) sulfide is ferrimagnetic, with the spin magnetic moments of the Fe cations in the tetrahedral sites oriented in the opposite direction as those in the octahedral sites, and a net magnetization. Both metal sites have high spin quantum numbers. The electronic structure of greigite is that of a half metal.