High‐Temperature X‐Ray Diffraction Study of the Polymorphism of MgSiO 3

An investigation of the polymorphic inversions of magnesium metasilicate (MgSiO 3 ) has been made with the aid of a Bureau of Standards X‐ray spectrometer furnace. This study, which involved the use of both natural and synthetic material, has yielded results which differ considerably from those of previous investigators. On the basis of these results a new scheme of relations between the three crystalline forms of MgSiO 3 —enstatite, protoenstatite, and clinoenstatite—has been proposed. According to this scheme protoenstatite is the stable high‐temperature form, and clinoenstatite is related to it somewhat as low cristobalite is related to high cristobalite. The significance of the new scheme of inversions in ceramic technology and in petrology is briefly discussed.