The ion beam-induced crystalline-to-amorphous transition has been investigated for crystalline phases in the Al2O3–SiO2system: Al2O3, SiO2(quartz), Al2SiO5(kyanite, andalusite, sillimanite), and 3Al2O3⋅2SiO2(mullite). Xe+1.5 MeV was used to irradiate samples at temperatures from 15 to 1023 Kin situin a transmission electron microscope to determine the critical amorphization doses. The susceptibility to amorphization is (highest to lowest): quartz, sillimanite, kyanite, andalusite, mullite, and alumina. These data are compared to viscosities and activation energies for viscous flow of melts in this system. The doses required for amorphization by ion irradiation are related to the viscosities of the melts. The activation energies for irradiation-enhanced annealing are qualitatively correlated with the activation energies of viscous flow. These results suggest a parallel between ion beam irradiation-induced amorphization and glass formation. Glass-forming “ability’’ correlates with susceptibility to radiation-induced amorphization. ©1997 American Institute of Physics.