A single-crystal sample of iron-rich schüllerite found at the Kahlenberg quarry in the Eifel paleovolcanic field (Germany) was studied by X-ray diffraction. The triclinic unit-cell parameters are as follows: a = 5.4061(1) Å, b = 7.0416(6) Å, c = 10.2077(7) Å, α = 99.86(1)°, β = 97.8(1)°, and γ = 89.98(1)°. The structure was solved by direct methods in sp. gr. P1 and refined to the R factor of 7.9% based on 4321 |F| > 6σ(F). The idealized formula is Ba2Na(Ca,Mn)(Fe2+,Fe3+)MgTi2[Si2O7]2O2(O,F)F. The new mineral differs from schüllerite by a lower sodium content and higher iron and calcium contents and is characterized by some distinguishing structural features. The dependence of the topology of layered HOH modules on the sodium content in schüllerite and lamprophyllite-group minerals and the character of regular intergrowths of these minerals are discussed.