Abstract
Abstract. Kahlenbergite, ideally KAl11O17, and Fe-rich hibonite, CaAl10Fe2O19, are high-temperature minerals found in “olive” subunits of pyrometamorphic rocks, in the Hatrurim Basin, the Negev desert, Israel. The crystal structures of both minerals are refined using synchrotron radiation single-crystal diffraction data. The structure of kahlenbergite (P63/mmc; a=5.6486(1) Å; b=22.8970(3) Å; Z=2) exhibits triple spinel blocks and so-called R blocks. The spinel blocks show mixed layers with AlO6 octahedra and (Al0.56Fe0.44)O4 tetrahedra and kagome layers with (Al0.92Fe0.08)O6 octahedra. One-dimensional diffuse scattering observed parallel to c* implies stacking faults in the structure. Also, in one of the investigated kahlenbergite crystals additional reflections can be identified, which obviously belong to a second phase with a smaller lattice parameter c: Fe3+-rich hibonite. The structure of hibonite contains the same spinel blocks as kahlenbergite. The R blocks in hibonite contain Ca atoms, AlO5 bipyramids, and AlO6 octahedra, whereas the R blocks in kahlenbergite contain potassium atoms and AlO4 tetrahedra.
Highlights
In one of the investigated kahlenbergite crystals additional reflections can be identified, which obviously belong to a second phase with a smaller lattice parameter c: Fe3+-rich hibonite
The R blocks in hibonite contain Ca atoms, AlO5 bipyramids, and AlO6 octahedra, whereas the R blocks in kahlenbergite contain potassium atoms and AlO4 tetrahedra
The β-alumina compounds with mono-valent cations, like sodium and potassium, are known as fast ion conductors
Summary
The β-alumina compounds with mono-valent cations, like sodium and potassium, are known as fast ion conductors They often exhibit nonstoichiometric composition and disordered structures (Collin et al, 1986a, b; Kim et al, 2018). The new mineral kahlenbergite (IMA2018-158) with the endmember formula KAl11O17 is found in small hematite segregations enriched by hibonite within wollastonite– gehlenite hornfels, north-east of Mt Parsa, the Hatrurim Basin, the Negev desert, Israel. It is a high-temperature mineral that occurs together with hibonite, corundum, hematite, dorrite and other anhydrous minerals. Kahlenbergite and associated minerals crystallize at temperatures of not less than 1000 ◦C under strongly oxidizing conditions
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