Barium calcium magnesium fluoride (Ba2(BaxCa1-x)Mg4F14, x=0.19-0.26) has been synthesized at 850 °C from precursors prepared by the solution precipitation method. Single crystals with composition of Ba2.200(2)Ca0.800(2)Mg4F14were obtained after prolonged heating. Lattice parameters from single crystal data are a = 12.4203(8) and c = 7.4365(5) Å [tetragonal, space group P42/mnm (No. 136)]. They increase with increasing barium concentration within a given stability window. The structure is built of a network of MgF6 octahedra forming a pyrochlore related channel system and isolated fluorine ions. Within the channels, heavy alkaline earth ions are located. The wide channel is filled with off-center positioned barium ions. The channel with a narrow cross section hosts both ions, Ca2+and Ba2+. The structure is isotypic with Pb3Nb4O12F2 but has a different coordination around Ba/Ca and Pb, respectively. Doped with ∼1% Eu(II), the compound shows intense blue luminescence under UV activation.