The crystal structures of rubidium boroleucite RbBSi₂O ₆ [a = 12.785(1) Å] and two silicon-rich solid solutions Rb_0.96(B_0.77Si_2.18)_2.95O ₆ [a = 12.858(1) Å] and Rb_0.92(B _0.46Si_2.42)_2.88O₆ [a = 12.914(1) Å] are refined in the space group I 4 3d (KBSi₂O₆ structural type) by the Rietveld method. Polycrystalline samples are prepared through the crystallization of glasses. The substitution Si⁴⁺ → B³⁺ in tetrahedra of the borosilicate framework occurs with the charge compensation due to a deficit of rubidium and boron. The formation of vacancies in tetrahedral positions leads to the breaking of bonds between tetrahedra, and bridging oxygen atoms become terminal atoms.