Geopolymer technology has emerged as an effective solution for the stabilization of industrial by-products and the immobilization of heavy metals. It has been established that the nature of the source materials used during synthesis has a significant effect on the final chemical and physical properties of the geopolymeric matrix. In particular, it has been established that the partial dissolution of specific wastes serves to either weaken or strengthen the newly formed structure. Moreover, leaching tests have shown that the use of either kaolinite or calcined kaolinite (metakaolinite) in fly ash based geopolymers affects the propensity of the matrix to immobilize heavy metals. This observation has practical implications for the application of geopolymer technology to the capping of mine tailings ponds or the backfilling of mines. The differences in dissolution behavior and the effect on final properties of geopolymeric materials have been studied for the kaolinite and metakaolinite system, with a view of gaining a wider appreciation of the behavior of other systems that are more difficult to study.