First natural hexaferrite with mixed beta -ferrite (beta -alumina) and magnetoplumbite structure from Jabel Harmun, Palestinian Autonomy

Ferrites of K and Ba close in composition to the known synthetic compounds KFe (super 2+) (sub 2) Fe (super 3+) (sub 15) O (sub 25) and BaMg (sub 2) Fe (super 3+) (sub 16) O (sub 27) 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): (K (sub 0.57) Ba (sub 0.38) Na (sub 0.05) ) (sub sigma 1) (Fe (super 3+) (sub 14.08) Mg (sub 1.42) Al (sub 0.80) Zn (sub 0.59) Ni (sub 0.16) Ca (sub 0.14) Cu (sub 0.09) Mn (sub 0.03) Ti (sub 0.03) Si (sub 0.02) ) (sub sigma 17.36) O (sub 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 (P6m2, Z = 2) with a = 5.9137(2) and c = 33.1450(15) Aa is different to that (P63/mmc) of the end-members and yields alternate stacking of beta -alumina type KMg (sub 2) Fe (sub 15) O (sub 25) and magnetoplumbite type BaMg (sub 2) Fe (sub 16) O (sub 27) "supermodules", each extending 1/2 of the unit cell along c. Raman spectroscopic study confirms the mixed character of K-Ba-ferrite structure. K-Ba-ferrite formed at non-equilibrium conditions and may be interpreted as an example of a nano-dissipative structure.