Due to magnesiums mobile nature, the plant will first break down chlorophyll in older leaves and transport the Mg to younger leaves which have greater photosynthetic needs. Therefore, the first sign of magnesium deficiency is the chlorosis of old leaves which progresses to the young leaves as the deficiency progresses. Magnesium also acts as an activator for many critical enzymes, including ribulosebisphosphate carboxylase (RuBisCO) and phosphoenolpyruvate carboxylase (PEPC), both essential enzymes in carbon fixation. Thus low amounts of Mg lead to a decrease in photosynthetic and enzymatic activity within the plants. Magnesium is also crucial in stabilizing ribosome structures, hence, a lack of magnesium causes depolymerization of ribosomes leading to premature aging of the plant. After prolonged magnesium deficiency, necrosis and dropping of older leaves occurs. Plants deficient in magnesium also produce smaller, woodier fruits. Magnesium deficiency in plants may be confused with zinc or chlorine deficiencies, viruses, or natural aging, since all have similar symptoms. Adding Epsom salts (as a solution of 25 grams per liter or 4 oz per gal) or crushed dolomitic limestone to the soil can rectify magnesium deficiencies. An organic treatment is to apply compost mulch, which can prevent leaching during excessive rainfall and provide plants with sufficient amounts of nutrients, including magnesium. See also
Magnesium in biology
Hypermagnesemia

References
External links

Magnesium
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.