First Terrestrial Occurrence of Kaitianite (Ti³⁺₂Ti⁴⁺O₅) from the Upper Mantle beneath Mount Carmel, Israel

Our nanomineralogical investigation of melt inclusions in corundum xenoliths from the Mount Carmel area, Israel, has revealed seven IMA-approved new minerals since 2021. We report here the first terrestrial occurrence of kaitianite (Ti³⁺₂Ti⁴⁺O₅). Kaitianite occurs as exsolution lamellae in tistarite (Ti₂O₃), in a melt inclusions together with a Ti,Al,Zr-oxide, a MgTi³⁺₂Al₄SiO₁₂ phase, spinel, sapphirine, Ti-sulfide, alabandite, and Si-rich glass in a corundum grain (Grain 1125C2). The chemical composition of kaitianite using electron probe microanalysis is (wt%) Ti₂O₃ 58.04, TiO₂ 37.82, Al₂O₃ 2.87, MgO 0.85, ZrO₂ 0.10, CaO 0.02, SiO₂ 0.02, sum 99.73, yielding an empirical formula of (Ti³⁺_1.78Al_0.12Ti⁴⁺_0.05Mg_0.05)(Ti⁴⁺_1.00)O₅, with the Ti³⁺ and Ti⁴⁺ partitioned, assuming a stoichiometry of three cations and five oxygen anions pfu. Electron back-scatter diffraction reveals that kaitianite has the monoclinic C2/c γ-Ti₃O₅-type structure with cell parameters: a = 10.12 Å, b = 5.07 Å, c = 7.18 Å, β = 112°, V = 342 ų, and Z = 4. Kaitianite is a high-temperature oxide phase, formed in melt pockets under reduced conditions in corundum-aggregate xenoliths derived from the upper mantle beneath Mount Carmel, Israel.