On the Polymorphism of Enstatite

The polymorphism of enstatite (MgSiO 3 ) is reviewed. Three stable phases occur—clinoenstatite, orthoenstatite, and protoenstatite, being stable at low, intermediate, and elevated temperatures, respectively — and new data concerning their crystallization from synthetic glasses are summarized. The phase transformations between these polymorphs are discussed, particularly their sensitivity to shear stresses. Finally, the possibility of using one or more of these transformations for toughening silicates is considered.