In the United States, for example, 733 tonnes of bismuth were consumed in 2016, of which 70% went into chemicals (including pharmaceuticals, pigments, and cosmetics) and 11% into bismuth alloys.Some manufacturers use bismuth as a substitute in equipment for potable water systems such as valves to meet "lead-free" mandates in the U.S. (began in 2014). This is a fairly large application since it covers all residential and commercial building construction.In the early 1990s, researchers began to evaluate bismuth as a nontoxic replacement for lead in various applications. Medicines
Bismuth is an ingredient in some pharmaceuticals, although the use of some of these substances is declining. Bismuth subsalicylate is used as an antidiarrheal; it is the active ingredient in such "pink bismuth" preparations as Pepto-Bismol, as well as the 2004 reformulation of Kaopectate. It is also used to treat some other gastro-intestinal diseases like shigellosis and cadmium poisoning. The mechanism of action of this substance is still not well documented, although an oligodynamic effect (toxic effect of small doses of heavy metal ions on microbes) may be involved in at least some cases. Salicylic acid from hydrolysis of the compound is antimicrobial for toxogenic E. coli, an important pathogen in travelers diarrhea. A combination of bismuth subsalicylate and bismuth subcitrate is used to treat the bacteria causing peptic ulcers. Bibrocathol is an organic bismuth-containing compound used to treat eye infections. Bismuth subgallate, the active ingredient in Devrom, is used as an internal deodorant to treat malodor from flatulence and feces.
The reaction conditions are critical to the process and determine the particle size.Iron(II) carbonate can also be thermally decomposed into Iron(II,III):
3FeCO3 → Fe3O4 + 2CO2 + CO

Reactions
Reduction of magnetite ore by CO in a blast furnace is used to produce iron as part of steel production process:

  
    
      
        
          
            
              Fe
              
                3
              
              
                
              
            
            
              O
              
                4
              
              
                
              
            
          
          +
          4
          
          CO
          ⟶
          
            3
            
            Fe
          
          +
          4
          
          
            CO
            
              2
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {{Fe3O4}+ 4CO -> {3Fe}+ 4CO2}}}
  Controlled oxidation of Fe3O4 is used to produce brown pigment quality γ-Fe2O3 (maghemite):

  
    
      
        
          
            
              
                
                  2
                  
                  
                    Fe
                    
                      3
                    
                    
                      
                    
                  
                  
                    O
                    
                      4
                    
                    
                      
                    
                  
                
                ⏟
              
            
            
              magnetite
            
            
              
            
          
          +
          
            
              
                1
                2
              
            
            
              O
              
                2
              
              
                
              
            
          
          ⟶
        
         
        
          
            
              
                
                  
                    
                      3
                      
                      
                        (
                        γ
                        
                          −
                        
                        
                          Fe
                          
                            2
                          
                          
                            
                          
                        
                        
                          O
                          
                            3
                          
                          
                            
                          
                        
                        )
                      
                    
                    ⏟
                  
                
                
                  maghemite
                
                
                  
                
              
            
          
        
      
    
    {\displaystyle {\ce {\underbrace{2Fe3O4}_{magnetite}+ {1/2O2}->}}\ {\color {Brown}{\ce {\underbrace{3(\gamma-Fe2O3)}_{maghemite}}}}}
  More vigorous calcining (roasting in air) gives red pigment quality α-Fe2O3 (hematite):

  
    
      
        
          
            
              
                
                  2
                  
                  
                    Fe
                    
                      3
                    
                    
                      
                    
                  
                  
                    O
                    
                      4
                    
                    
                      
                    
                  
                
                ⏟
              
            
            
              magnetite
            
            
              
            
          
          +
          
            
              
                1
                2
              
            
            
              O
              
                2
              
              
                
              
            
          
          ⟶
        
         
        
          
            
              
                
                  
                    
                      3
                      
                      
                        (
                        α
                        
                          −
                        
                        
                          Fe
                          
                            2
                          
                          
                            
                          
                        
                        
                          O
                          
                            3
                          
                          
                            
                          
                        
                        )
                      
                    
                    ⏟
                  
                
                
                  hematite
                
                
                  
                
              
            
          
        
      
    
    {\displaystyle {\ce {\underbrace{2Fe3O4}_{magnetite}+ {1/2O2}->}}\ {\color {BrickRed}{\ce {\underbrace{3(\alpha-Fe2O3)}_{hematite}}}}}

Structure
Fe3O4 has a cubic inverse spinel group structure which consists of a cubic close packed array of oxide ions where all of the Fe2+ ions occupy half of the octahedral sites and the Fe3+ are split evenly across the remaining octahedral sites and the tetrahedral sites.