Abstract Further information on defects previously [J. Gastaldi et al. Phil. Mag. Lett. 72 (1995) 311.] observed by X-ray topography in quasicrystalline grains, and that show a loop-shaped contrast, was obtained by combining this technique with electron microscopic observations and chemical analyses. The experiments, carried out either at room temperature or during in situ and real-time high temperature annealing, allowed to get clues on the relationships between these loop-shaped defects, the growth process of the quasicrystal grains and the defect behaviour under the annealing treatment.