Iron (II, III) oxide

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Crystal structure
Crystal structure of magnetite
__ Fe 3+      __ Fe 2+      __ O 2−
Surname Iron (II, III) oxide
other names
  • Triiron tetraoxide
  • Magnetite (mineral)
  • Hammer blow
Ratio formula Fe 3 O 4
Brief description

deep black, ferrimagnetic powder

External identifiers / databases
CAS number
  • 1317-61-9 (triiron tetraoxide)
  • 1309-38-2 (magnetite)
EC number 215-277-5
ECHA InfoCard 100,013,889
PubChem 16211978
Wikidata Q411235
Molar mass 231.54 g mol −1
Physical state



5.2 g cm −3

Melting point

1538 ° C


almost insoluble in water

safety instructions
GHS labeling of hazardous substances
no GHS pictograms
H and P phrases H: no H-phrases
P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Iron (II, III) oxide is an oxide of iron that contains both divalent and trivalent iron. It has the chemical formula FeO · Fe 2 O 3 or Fe 3 O 4 and is therefore also known as triiron tetraoxide . It is found in nature as magnetite . The melting point is 1538 ° C.


Hammer strike on an anvil

From iron and oxygen at very high temperatures:

Made of iron and water vapor at temperatures below 560 ° C

Made of iron (III) oxide at temperatures above 1200 ° C

From iron (III) oxide by reduction with hydrogen

As iron hammer or scale was formerly called the parachutist when forging hot iron iron particles immediately in air to Fe 3 O 4 oxidized.

Sinter is another name for the iron oxides that occur in continuous casting in the manufacture of steel slabs and in the hot rolling of steel. When the hot steel comes into contact with atmospheric oxygen, iron oxides are formed on the surface of the slabs, which in addition to iron (III) oxide contain a high proportion of magnetite.


Black, temperature-resistant, ferrimagnetic substance with spinel structure . Insoluble in water, acids and alkalis, but soluble in hydrofluoric acid.


As a pigment iron oxide black for temperature-resistant, black coloring. As a magnetic pigment ( magnetic pigment ) for audio and video tapes.

One of the most important applications is as an inexpensive catalyst with a long service life in the Haber-Bosch process for the synthesis of ammonia . Magnetite also serves as a catalyst component in the dehydrogenation of ethylbenzene to styrene .

Individual evidence

  1. Entry on iron oxides. In: Römpp Online . Georg Thieme Verlag, accessed on July 15, 2014.
  2. a b c d e Entry on iron (II, III) oxide in the GESTIS substance database of the IFA , accessed on December 21, 2019(JavaScript required) .
  3. a b Georg Brauer (Ed.) U. a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume III, Ferdinand Enke, Stuttgart 1981, ISBN 3-432-87823-0 , p. 1647.