This paper investigates the CaO-Al2O3-SiO2 system glass. When the glasses were heat treated at different temperatures and times, they crystallized from the surface. The main crystals were dendrites of anorthite (CaAl2Si2O8). The morphology of crystallization was observed using scanning electron microscopy, and the crystal size was measured by optical microscopy. It was found that the growth of anorthite (CaAl2Si2O8) crystals was diffusion controlled. The apparent activation energy for crystal growth was about 581 kJ/mol. The rate of crystal growth was not constant during the growth process; the rate was highest at the beginning of crystallization and gradually decreased with increasing time. The higher the temperature, the less time required to complete crystal growth. The total process of diffusion may be determined by the diffusion rate of Ca2+. 1998 Elsevier Science Ltd.