The framework structure of the synthetic microporous lithosilicate RUB-30 (K_2.6Li_5.4[Li₄Si₁₆O₃₈]·4.3H₂O) is similar to that of the fibrous zeolites such as natrolite, edingtonite and thomsonite, since all their frameworks include the same secondary structural building unit, the so-called 4–1 T ₅O₁₀ cluster of tetrahedra. Unique to the structure of RUB-30, each 4–1 unit consists of a LiSi₄O₁₀ moiety within which the single [LiO₄] tetrahedron is strictly segregated from the other four [SiO₄] tetrahedra. The connection of neighboring 4–1 units through edge-sharing [LiO₄] tetrahedra results in a new framework topology. The present work reports an `average' structure of RUB-30 solved by synchrotron X-ray single-crystal diffraction data collected at a second-generation source. A superstructure with a × 2b × c (relative to the subcell quoted above) could be seen in X-ray diffraction data collected with better resolution and higher brightness at a third generation source. Diffuse streaks along k with l = odd and unusual superstructure hkl reflections, with k = odd and l = odd only, indicate a more complicated real structure of the material. To explain this observation we propose two different structure types which are statistically, but coherently, intergrown in RUB-30.