Surface energy of fayalite and its effect on Fe-Si-O oxygen buffers and the olivine-spinel transition

Abstract

The surface energy (hydrated surfaces) of fayalite (α-Fe2SiO4) was determined to be 2.47 ± 0.25 J/m2 using high-temperature oxide melt solution calorimetry. This is larger than the surface energy of magnetite (Fe3O4), but lower than that of forsterite (α-Mg2SiO4). The changes in the positions of the quartz-fayalite-magnetite (QFM) and quartz-iron-fayalite (QIF) buffers with particle size reduction were calculated. QFM is lowered in fO2 by 3-7 log units as a function of temperature for 30 nm particles while QIF is raised by 1-2 log units. The estimated surface energy difference between olivine and spinel polymorphs decreases the pressure of the olivine-spinel transition in Fe2SiO4 by about 1 GPa.