Synthesis of hexacelsian barium aluminosilicate (BaAl2Si2O8 or BAS) from BaCO3,Al2O3,and amorphous SiO2 was examined. BaCO3 can react with SiO2 and Al2O3 to form barium silicates (Ba2SiO4 or B2S, BaSiO3 or BS, and BaSi2O5 or BS2) and barium aluminate (BaAl2O4 or BA), It is shown that there are two competitive reactions leading to the formation of hexacelsian BAS, One involves a reaction between BS2 and Al2O3 and the other involves a reaction between BA and SiO2. In experiments with the model BS2-Al2O3 and BASiO(2) systems it is shown that the reaction between BS, and Al2O3 is much faster than the reaction between BA and SiO2. However, in the BAS system, Al2O3 suppresses the reactions which form BS, and instead reacts,vith B2S and BS to form BA, The kinetics of hexacelsian BAS formation are greatly enhanced when BS, is made separately and fired with Al2O3 to yield BAS.