text: In the 1950s, Viktor Glukhovsky developed concrete materials originally known under the names "soil silicate concretes" and "soil cements", but since the introduction of the geopolymer concept by Joseph Davidovits, the terminology and definitions of the word geopolymer have become more diverse and often conflicting. The word geopolymer is sometimes used to refer to naturally occurring organic macromolecules; that sense of the word differs from the now-more-common use of this terminology to discuss inorganic materials which can have either cement-like or ceramic-like character.
  In the following presentation, a geopolymer is essentially a mineral chemical compound or mixture of compounds consisting of repeating units, for example silico-oxide (-Si-O-Si-O-), silico-aluminate (-Si-O-Al-O-), ferro-silico-aluminate (-Fe-O-Si-O-Al-O-) or alumino-phosphate (-Al-O-P-O-), created through a process of geopolymerization. This method of describing mineral synthesis (geosynthesis) was first presented by Davidovits at an IUPAC symposium in 1976.
  Even within the context of inorganic materials, there exist various definitions of the word geopolymer, which can include (or not) a relatively wide variety of low-temperature synthesized solid materials. The most typical geopolymer is generally described as resulting from the reaction between metakaolin (calcined kaolinitic clay) and a solution of sodium or potassium silicate (waterglass). The chemical reaction of geopolymerization tends to result in a highly-connected, disordered network of tetrahedral oxide units - which are silicate and aluminate tetrahedra in the metakaolin-waterglass example mentioned above - and with the net negative charges that are associated with aluminate tetrahedra being balanced by the sodium or potassium ions. 
  In the simplest form, an example chemical formula for a geopolymer can be written as NaO·AlO·nSiO·wHO, where n is usually between 2 and 4, and w is around 11-15. Geopolymers can be formulated with a wide variety of substitutions in both the framework (Si,Al) and non-framework (Na) sites; most commonly K or Ca take on the non-framework (Na) sites, or Fe or P can in principle replace some of the Al or Si.
  Geopolymerization usually occurs at ambient or slightly elevated temperature; the solid aluminosilicate raw materials (e.g. metakaolin) dissolve into the alkaline solution, and then cross-link and polymerize into a growing gel phase, which then continues to set, harden and gain strength.