Gallioaluminosilicate hydrogels with composition 0.1 Ga2O3 : 0.9 Al2O3 : 10 SiO2 : 4.0 Na2O : 150 H2O were prepared using sodium aluminate, colloidal silica, and a soluble galliosilicate with composition Ga2O3 : 15 SiO2 : 10 Na2O : 400 H2O as a source of gallia. The hydrothermal transformation of these gels at 95 degrees C yields crystals with the faujasite structure when the crystallization reaction is performed in the absence of stirring and with the gmelinite structure (with minor amount of Pt) when crystallization is completed with stirring of the hydrogel. The crystallization time for Na(Ga,Al)Y can be decreased to 15 h from 38 h by raising the crystallization temperature to 110 degrees C from 95 degrees C, The calcined Na(Ga,Al)Y crystals have surface area in the 600 to 660 m(2)/g range and, unless La-stabilized, suffer partial lattice degradation when, following an exchange with an NH4NO3 solution, the NH4(Ga,Al)Y crystals are calcined at 500 degrees C in air. This finding is clearly indicated by Al-27, Ga-71, and Si-29 MAS NMR spectroscopic results. The Si-29 NMR spectra of samples exchanged and calcined in the absence of La are poorly resolved and their quantitative analysis indicates substantial loss of Al and Ga from the faujasite framework. Consistent with this interpretation, Al-27 MAS NMR spectra reveal large amounts of octahedrally coordinated species in H(Ga,Al)Y. Moreover, the Ga-71 spectra show no evidence of tetrahedrally coordinated framework Ga. In contrast, the multinuclear NMR data of the H(Ga,Al,La)Y crystals indicate only minor Al and Ga losses from the framework, thus revealing the stabilizing influence of La, Thermodesorption of pyridine and microcalorimetry results with NH3 have indicated that the La-stabilized H(Ga,Al,La)Y crystals have a more moderate acidity than the reference HY sample. Model fluid cracking catalyst (FCC)-containing H(Ga,Al,La)Y crystals are more active when cracking gas oil under microactivity testing conditions than similarly prepared FCC-containing HY-type zeolites and a reference equilibrium catalyst containing a rare-earth-stabilized HY, indicating that these crystals should be considered as acidic components in commercial FCC preparations. (C) 2000 Academic Press.