Two uranium and two thorium silicates were obtained using high temperature mixed fluxes methods. K-14(UO2)(3)Si10O30 crystallizes in the P2(1)/c space group and contains open-branched sechser (six) single silicate chains, whereas K-2(UO2)Si2O6 crystallizes in the C2/c space group and is built of unbranched achter (eight) silicate chains. The crystals of K-14(UO2)(3)Si10O30 and K-2(UO2)Si2O6 are related by increasing U/Si molar ratios, and both structures contain the same secondary building units (SBUs), [USi6] heptamers. The triangle diagram for all known A(+)-UO22+-SiO44- phases demonstrates the high polymerization level of silicate groups in the system, which was compared with the family of A(+)-UO22+-BO33-/BO45- compounds. For both thorium silicates, the transformation of K2ThSi2O7 to K2ThSi3O9 was found to be a factor of the reaction time. K2ThSi2O7 crystallizes in the C2/c space group and belongs to the (Na2SiSi2O7)-Si-vi structure type. Its 3D framework consists of diorthosilicate Si2O7 group and ThO6 octahedra. Noncentrosymmetric K2ThSi3O9 crystallizes in the hexagonal P6(3) space group and adopts mineral wadeite-type structure based upon triorthosilicate Si3O9 rings and ThO6 octahedra. The coordination environment of thorium for all existing oxo-anion compounds including B, Si/Ge, P/As, Cr/Mo/W, and S/Se/Te are summarized and analyzed. Additionally, spectroscopic properties of all novel materials have been studied.