sentences:  The examples below were taken from 2011 scientific publications, written by scientists with different backgrounds.Definitions of the term geopolymer
  
  "For chemists"
  
  "For geopolymer material chemists"
  
  "For alkali-cement scientists"
  
  "For geopolymer ceramic chemists"
  
  "For ceramic scientists"
  
  In 1937, W. L. Bragg published a method for classifying all kinds of silicates and their crystal structures based on the concept of the ionic theory by Linus Pauling.The fundamental unit is a tetrahedral complex consisting of a small cation such as Si4+, or Al3+ in tetrahedral coordination with four oxygens (Pauling's first rule).