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