Stoichiometric end member galloalunites of the general formula AGa(3)(SO4)(2)(OH)(6), with A = Na+, K+ Rb+), H3O+, and NH4+ have been synthesized under hydrothermal conditions. These galloalunites were characterized by chemical methods, thermal analysis (DSC, TG coupled with mass spectroscopy), and powder X-ray diffraction (XRD). The stages of thermal decomposition of sodium, potassium and rubidium galloalunite show a common decomposition mechanism forming beta-Ga2O3 and A(2)SO(4) (A= Na+, K+, and Rb+) while ammonium and oxonium galloalunite decompose under formation of pure beta-Ga2O3. The thermogravimetric results confirmed the analytical results on the galloalunites and thereby verified the stoichiometry of these synthetic products. Galloalunites with different monovalent cations in A site (i.e. Na+, K+, Rb+), H3O+ and NH4+) crystallize in the rhombohedral space group R (3) over barm (#166). The effects of substitution on the unit cell parameters are rationalized in terms of the structural arrangements in galloalunites. The unit cell parameter c increases with increasing effective ionic radii of the cation in the A site, whereas the parameter a changes to a much lesser degree. (C) 2011 Elsevier B.V. All rights reserved.