Single crystals of K-8(K5F)U6Si8O40 were grown from a mixed alkali halide flux. K-8(K5F)U6Si8O40 is the first intergrowth uranyl silicate, being composed of alternating slabs related to two previously reported uranyl silicates: Cs2USiO6 and [Na9F2][(UO2)(2)(UO2)(2)(Si2O7)(2)]. It exhibits intense luminescence, which is influenced by the [(UO2)(2)O] dimers present in the structure.