High resolution electron microscopic studies on ferrosilite III

High resolution transmission electron microscopic (HRTEM) studies on ferrosilite (Fs) III confirmed the periodicity nine (p=9) of the tetrahedral chains in this silicate. Various chain periodicity faults (CPFs) have been observed and faults with “elfer” units (p′=11) dominate. CPFs with p′?9 were observed and are interpreted as pyroxene like slabs. Synthesis of Fs III under extended run duration demonstrated that Fs III actually is the stable phase in the system FeSiO₃ at high pressures and high temperatures. However, the stability fields of Fs III and orthoferrosilite might be separated by a narrow field of a FeSiO₃ polymorph with “elfer” single chain. This field has not been bracketed so far. New structure variants of Fs are discussed. Reconnaissance experiments on the kinetics of CPFs are reported.