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Ferrites of K and Ba close in composition to the known synthetic compounds KFe22+Fe153+O25 and BaMg2Fe163+O27 were found in a thin vein, filled with magnesioferrite and khesinite, in pyrometamorphic flamite-gehlenite hornfels of the Hatrurim Complex, Palestinian Autonomy. Both ferrites are characterized by a modular structure composed of 5-layered spinel (S) blocks interstratified with R-blocks. The R-modules of K-ferrite are of the beta-alumina type whereas those in Ba-ferrite are of the magnetoplumbite type. Rare grains of K-Ba-ferrite of intermediate composition with the empirical crystal chemical formula (EPMA): (K0.57Ba0.38Na0.05)(Sigma 1)(Fe14.083+Mg1.42Al0.80Zn0.59Ni0.16 Ca0.14Cu0.09Mn0.03Ti0.03Si0.02)Sigma O-17.36(25.54), were also discovered. The structure of the natural mixed potassium-barium ferrite was investigated by single-crystal X-ray diffraction. The hexagonal space-group symmetry (Y (6) over bar2, Z= 2) with a = 5.9137(2) and c = 33.1450(15)angstrom is different to that (P6(3)/mmc) of the end-members and yields alternate stacking of beta-alumina type KMg2Fe15O25 and magnetoplumbite type BaMg2Fe16O27 "supermodules", each extending 1/2 of the unit cell along c. Raman spectroscopic study confirms the mixed character of K-Ba-ferrite structure. K-Baferrite formed at non-equilibrium conditions and may be interpreted as an example of a nano-dissipative structure.