Petrified wood is a member of the quartz family. It’s not actually wood, but rather a fossilized form of wood or other plant material.  
It forms when wood (or other plants) are buried and protected from decay. Underground water dissolve the solids and the original plant is replaced by silica (quartz), calcite, pyrite and even opal. The wood is sort of like a mold for the other minerals to form in. These pieces can be millions of years old! 
 
                         
         
         
         
    
    
      
      
        
      
      
    
      
      
        
          
        
      
      
        
        
          
        
        
 
      
    
      
      
        
          
        
      
      
        
        
          
        
        
 
      
    
   
    
    
      
      
        
      
      
        
        
          
        
        
 
      
    
      
      
        
      
      
        
        
          
        
        
 
      
    
   
    
    
      
      
        
      
      
        
        
          
        
        
 
      
    
      
      
        
      
      
        
        
          
        
        
 
      
    
   
    
    
      
      
        
      
      
        
        
          
        
        
 
      
    
   
    
    
      
      
        
      
      
    
      
      
        
          
        
      
      
        
        
          
        
        
