Abstract
Mechanism of the transformation of forsterite to modified spinel structure has been studied using multi-anvil apparatus. In order to examine the effect of stress on the transformation mechanism, forsterite single crystals were placed in two different media of powdered forsterite and NaCl, where the latter medium was found to provide one order of magnitude smaller differential stress in the sample. Optical and transmission electron microscope observations for the run products at 15.5GPa, 1000°C clearly show evidence which supports the in coherent nucleation and growth mechanism for the olivine-modified spinel transformation in these experimental conditions. The present results, combined with those of earlier works, suggest that the other possible mechanism, a martensitic transformation, may be realized only under substantially large differential stress of over 2GPa for the olivine-modified spinel transformation in Mg2SiO4.
