Prepd from an aq soln of an equimolecular mixture of guanidine sulfate and aluminum sulfate: Ferraboschi, Proc. Cambridge Philos. Soc. 14, 473 (1908); Holden et al., Phys. Rev. 101, 962 (1956); Wieder, Proc. IRE 45, 1094 (1957). Crystal structure: Schein et al., J. Chem. Phys. 47, 5183 (1967). Crystal growth: T. A. Zarembovskaya, Zh. Fiz. Khim. 45, 2504 (1971). Optical properties: P. M. Nikolic et al., Fizika (Zagreb) 12, Suppl. 1, 165 (1980).