Characterization of Gadolinite-Group Minerals Using Crystallographic Data Only: The Case of Hingganite-(Y) From Cuasso Al Monte, Italy

Important data concerning chemical composition of a mineral of the gadolinite group can be obtained from a refinement of its crystal structure. In spite of the complexities, an entirely crystallographic procedure performed on a single grain can afford a practical way to identify and characterize these species; such a procedure is often successful, provided the quality of the cry stal allows it. We consider the crystal-chemical mechanisms corresponding to the most important substitutions, and apply such a method to identify the Fe-poor and Ca-rich gadolinite-group minerals from Cuasso al Monte, Varese, Italy. These crystals can be ascribed to hingganite-(Y), with minor amounts of gadolinite (0.26–0.31 molar fraction) and datolite components (0.15–0.25 molar fraction) in solid solution. The component minasgeraisite-(Y) is not present, even as a minor one, in the samples studied .