Iron sulfide, also known as ferric sulfide or sesquisulfide, is one of the three iron sulfides besides FeS

Iron(II) sulfide

Iron sulfide or ferrous sulfide is a chemical compound with the formula . In practice, iron sulfides are often non-stoichiometric. Powdered iron sulfide is pyrophoric Iron(II) sulfide or ferrous sulfide (Br.E. sulphide) is a chemical compound with the formula . In practice, iron sulfides are...

 and FeS₂

FeS2

FeS2 may refer to:Iron sulphide crystal systems:*Pyrite*Marcasite...

. It is a solid, black powder but decays at ambient temperature into a yellow-green powder.

This is a relatively unstable artificial product that does not occur in nature.

Preparation and properties

Fe₂S₃ is prepared by addition of refrigerated iron(III) chloride

Iron(III) chloride

Iron chloride, also called ferric chloride, is an industrial scale commodity chemical compound, with the formula FeCl3. The colour of iron chloride crystals depends on the viewing angle: by reflected light the crystals appear dark green, but by transmitted light they appear purple-red...

 dilution to also cooled sodium sulfide

Sodium sulfide

Sodium sulfide is the name used to refer to the chemical compound Na2S, but more commonly it refers to the hydrate Na2S·9H2O. Both are colorless water-soluble salts that give strongly alkaline solutions...

dilution.

2 FeCl₃ + 3 Na₂S → Fe₂S₃↓ + 6 NaCl

which decays at a temperature over 20°C into FeS and sulphur.
Holleman, Wiberg: Inorganic Chemistry (2001), p. 1451; ISBN 0-12-352651-5

Fe₂S₃ → 2 FeS + S↓

With hydrochloric acid it decays according to the following reaction equation:
H. Roempp, Chemie (1997), S. 1099; ISBN 3-13-734710-6

Fe₂S₃ + 4 HCl → 2 FeCl₂ + 2 H₂S↑ + S↓