Iron(III) sulfide

Iron(III) sulfide, also known as ferric sulfide or sesquisulfide, is one of the several binary iron sulfides. It is a solid, black powder that degrades at ambient temperature.

Reactions
precipitates from solutions containing its respective ions:
 * 2Fe3+ + 3S2&minus; → Fe2S3

The resulting solid decays at a temperature over 20 °C into iron(II) sulfide (FeS) and elemental sulfur:
 * Fe2S3 → 2 FeS + S

With hydrochloric acid it decays according to the following reaction equation:
 * Fe2S3 + 4 HCl → 2 FeCl2+ 2 H2S + S

Greigite
Greigite, with the chemical formula Fe^{2+}Fe^{3+}2S4, is a mixed valence compound containing both Fe(III) and Fe(II). It is the sulfur equivalent of the iron oxide magnetite (Fe3O4). As established by X-ray crystallography, the S anions form a cubic close-packed lattice, and the Fe cations occupy both tetrahedral and octahedral sites.