Abstract: | A series of isotypic silicates of composition RE2MSiO4]2 (OH) with RE = La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, and M = Al3+, Fe3+ has been synthesized under hydrothermal conditions. Lattice constants of two members as determined from single crystal X-ray diffraction data are: La2AlSiO4]2 (OH) (La2FeSiO4]2 (OH)) , , , gb = 112.4 (112.5°), , Z=4. |