Surface energy of fayalite and its effect on Fe-Si-O oxygen buffers and the olivine-spinel transition
Surface energy of fayalite and its effect on Fe-Si-O oxygen buffers and the olivine-spinel transition
American Mineralogist (October 2018) 103 (10): 1599-1603
- buffers
- calorimetry
- experimental studies
- fayalite
- framework silicates
- high pressure
- high temperature
- laboratory studies
- magnetite
- mineral surface
- nesosilicates
- olivine
- olivine group
- orthosilicates
- oxides
- oxygen
- phase transitions
- polymorphism
- pressure
- quartz
- silica minerals
- silicates
- spinel
- temperature
- thermochemical properties
- thermodynamic properties
- surface energy
The surface energy (hydrated surfaces) of fayalite (alpha -Fe (sub 2) SiO (sub 4) ) was determined to be 2.47 + or - 0.25 J/m (super 2) using high-temperature oxide melt solution calorimetry. This is larger than the surface energy of magnetite (Fe (sub 3) O (sub 4) ), but lower than that of forsterite (alpha -Mg (sub 2) SiO (sub 4) ). 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 fO (sub 2) 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 Fe (sub 2) SiO (sub 4) by about 1 GPa.