A new vanadium(IV) silicate, Rb-2(VO)(Si4O10).xH(2)O (x approximate to 0.1), has been synthesized by a high-temperature, high pressure hydrothermal method. It crystallizes in the tetragonal space group 14(1)md (No. 109) with a = 12.2225(7) Angstrom, c = 7.7948(6) Angstrom, and Z= 4. The structure consists of spiral chains of corner-sharing SiO4 tetrahedra linked to neighboring chains via corner sharing to form a 3-D silicate framework which delimits channels to accommodate the VO2+ groups. The Rb+ ions are located in the cavities within the silicate framework. Magnetic susceptibility confirms the valence of vanadium. A partially occupied lattice water site is confirmed by IR and solid state H-1 NMR spectroscopy. The structure of the title compound is considerably different from those of the synthetic silicate K-2(VO)(Si4O10).H2O and the two polymorphs of the natural mineral Ca(VO)(Si4O10).4H(2)O, although they have identical framework stoichiometry.