Direct observation of crystallization of amorphous Mg-bearing silicate grains into Mg2SiO4 (forsterite)

The crystallization of amorphous Mg-bearing silicate grains into Mg2SiO4 and its temperature dependence were clarified by observing the grains in situ while heating in a transmission electron microscope. The crystallization started from the grain surface at 800 'C. Before the crystallization at the grain surface, the formation of a rim-like layer due to prenucleation was observed. The characteristic structure change of the grains was recorded and indicated that prenucleation occurred before crystallization. This phenomenon probably corresponds to the "stall" idea suggested by Hallenbeck & Nuth (1998, Ap&SS, 255, 427) in the crystallization of silicate.