For technologically important borosilicate glass and crystalline phases, the structure of K1−xRbxBSi2O6 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) solid solutions has been investigated employing X-ray diffraction data. Glass samples were prepared by a melt quenching from 1250–1300 °C for 0.5–1 hour. For glass samples glass transition(Tg), crystallization (Tcryst) and melting (Tm) temperatures were determined by differential scanning calorimetry. To investigate the glass structure, angle-dispersive X-ray diffractometry was applied by using an energy-resolving semiconductor detector. The radial distribution functions (RDFs) were calculated. Comparing correlation distances of glass RDFs and mean interatomic distances calculated for polycrystalline samples, the conclusion is drawn that in the glass state not only TO4 (T = Si, B) tetrahedra as stable structure-units but two corner sharing tetrahedra and apparently fourfold rings from tetrahedra exist. Read More: http://www.oldenbourg-link.com/doi/abs/10.1524/zkri.2012.1