Granular and needle-like crystals were observed in mullite made from Al(OH)(3) and kaolinite gangue using SEM and EDS. It's found that the granular mullite crystals are in the Al(OH)(3) pseudomorphs but the needle-like mullite crystals are in the gangue pseudomorphs. The differences of crystal shape of mullite come from the secondary mullitization based on the difference between the original shape of the Al2O3 crystallites and mullite crystallites in the pseudomorphs. With increases in the sintering temperature and additions of MgCO3, the differences of shape of mullite crystals become small.

Keywords: Crystal shape; Mullite; Al(OH)(3); Kaolinite