Qeltite – the first terrestrial high-temperature mineral with a langasite-type structure from the pyrometamorphic rocks of the Hatrurim Complex

Qeltite (IMA2021–032), ideally Ca 3 Ti(Fe 2 Si)Si 2 O 14 , was found in gehlenite–rankinite–wollastonite paralava from a pyrometamorphic rock of the Hatrurim Complex at Nabi Musa locality, Judean Desert, West Bank, Palestine. It generally occurs as light-brown flattened crystals up to 40–50 μm in length and less than 5 μm in thickness. Its aggregates reach 100–200 μm in size. Its empirical crystal chemical formula based on 14 O is: (Ca 2.96 Sr 0.02 Mn 0.01 ) Σ2.99 Ti 4+ (Fe 3+ 1.59 Si 0.60 Al 0.43 Ti 4+ 0.38 Cr 0.01 ) Σ3.01 (Si 1.99 P 0.01 ) Σ2 O 14 . The strongest reflections in its calculated X-ray diffraction pattern are [ d , Å, ( I , %), hkl ]: 3.12, (100), 111; 2.85, (61), 201; 2.85, (48), 021; 2.32, (45), 211; 6.93, (31), 100; and 1.81, (30), 212. Qeltite is trigonal and crystallises in the noncentrosymmetric P 321 space group, with a = 8.0077(5) Å, c = 4.9956(4) Å, V = 277.42(4) Å 3 and Z = 1. Its microhardness VHN 25 is 708(17) kg/mm 2 and its hardness on the Mohs scale is ~6. Its calculated density is 3.48 g/cm 3 . It was found in fine-grained mineral aggregates within coarse-grained main minerals of rankinite–gehlenite paralava with subordinate wollastonite, Ti-bearing andradite and kalsilite. In these aggregates, the mineral is associated with khesinite, paqueite and pseudowollastonite, indicating a high-temperature genesis (~1200°C). Its crystallisation can be compared with the crystallisation of minerals containing refractory inclusions in meteorites.