3
          
          Fe
          +
          4
          
          
            H
            
              2
            
            
              
            
          
          O
          ⟶
          
            Fe
            
              3
            
            
              
            
          
          
            O
            
              4
            
            
              
            
          
          +
          4
          
          
            H
            
              2
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {3Fe + 4H2O->Fe3O4 + 4H2}}}
  
Under anaerobic conditions, ferrous hydroxide (Fe(OH)2) can be oxidized by water to form magnetite and molecular hydrogen.
Iron(II,III) oxide is the chemical compound with formula Fe3O4. It occurs in nature as the mineral magnetite. It is one of a number of iron oxides, the others being iron(II) oxide (FeO), which is rare, and iron(III) oxide (Fe2O3) which also occurs naturally as the mineral hematite. It contains both Fe2+ and Fe3+ ions and is sometimes formulated as FeO ∙ Fe2O3. This iron oxide is encountered in the laboratory as a black powder. It exhibits permanent magnetism and is ferrimagnetic, but is sometimes incorrectly described as ferromagnetic. Its most extensive use is as a black pigment. For this purpose, it is synthesized rather than being extracted from the naturally occurring mineral as the particle size and shape can be varied by the method of production. Preparation
Heated iron metal interacts with steam to form iron oxide and hydrogen gas.