9362R: Jianmuite, ZrTi4+Ti3+5Al3O16, a new mineral from the Allende meteorite and from chromitite near Kangjinla, Tibet, China

Abstract

The new mineral jianmuite, ZrTi4+Ti3+5Al3O16 (IMA No. 2023-057) was found (1) as an inclusion in a corundum grain from the Cr-11 orebody near Kangjinla (29°11’N, 92°18’E), Tibet, China with wenjiite, Ti10(Si,P,☐)7, Al-rich spinel, osbornite, TiN, a Ca-amphibole particularly enriched in Ti, a Sr-rich dmisteinbergite, CaAl2Si2O8, and amorphous phases (probably residual melt) (holotype and first co-type) and (2) as several grains with corundum, mullite, Al6Si2O13, tistarite, Ti2O3, and kaitianite, Ti3+2Ti4+O5, in the matrix of the CV3 carbonaceous chondrite Allende (second co-type). Eight energy-dispersive spectroscopic analyses of the holotype normalized to 100% gave SiO2 1.83, ZrO2 23.17, Al2O3 18.41, Ti2O3 54.32, Sc2O3 1.25, MgO 1.03, Total 100.00 wt%. The empirical formula calculated on the basis of 10 cations and 16 oxygen atoms is VIIIZr VII(Ti3+3.034Ti4+0.602Zr0.364)Σ4.000VI(Ti3+1.845Al1.838Mg0.186Sc0.131)Σ4.000IV(Al0.780Si0.220)Σ1.000 O16. The simplified formula is Zr(Ti3+,Ti4+,Zr)4(Ti3+,Al)4(Al,Si)O16 and the ideal chemical formula is ZrTi4+Ti3+5Al3O16, which requires ZrO2 17.23 calculated wt%, TiO2 11.16 calculated wt%, Ti2O3 50.23 calculated wt% and Al2O3 21.38 calculated wt%, Total 100 wt.%. Six energy-dispersive spectroscopic analyses of the first co-type normalized to 100% gave SiO2 2.86, ZrO2 23.06, Al2O3 18.10, Ti2O3 53.78, Sc2O3 1.17, MgO 1.04, Total 100.00 wt%. Three-dimensional electron diffraction of the holotype determined jianmuite as I-centered tetragonal, space group: (I-4) (# 82), with a = 10.3675 (10) Å, b = 10.3675 (10) Å, c = 9.8125 (10) Å, V = 1054.70 (18) Å3 and Z = 4. Wavelength-dispersive spectroscopic electron probe microanalyses of Allende jianmuite (second co-type) gave for the two grains (5 analyses each) SiO2 2.32, 3.02, ZrO2 13.95, 10.79, Al2O3 26.82, 21.83, Ti2O3 44.68, 49.47, TiO2 12.62, 14.75, Sc2O3 0.12, 0.04, MgO 0.19, 0.80, FeO, 0.52, 0.55, CaO 0.17, 0.08, Total 101.40, 101.34 wt%.Weight% TiO2 and weight% Ti2O3 were calculated from formula units Ti+4 and Ti+3, which were determined assuming a stoichiometry of 10 cations and 16 oxygen atoms. Electron backscatter diffraction (EBSD) patterns on the Allende jianmuite (second co-type) can be indexed by the tetragonal I-4 structure obtained on the holotype, with a mean angular deviation of ~0.7°, thereby confirming identification of the Allende mineral as jianmuite. The structure of jianmuite consists of cations packed in distorted I-centered cubes. There are 8 independent cation sites, two inside distorted cubes with tetragonal ridged faces (CN = 8), two inside capped trigonal prisms (CN = 7), two inside distorted octahedra (CN = 6) and two inside tetrahedra (CN = 4). All coordination polyhedra are connected by edges, except for the tetrahedra, which are connected by vertexes with other polyhedra. Despite the similarity in composition with carmeltazite, ZrTi3+4Al2O11, the structures of the two minerals bear little resemblance to one another, most notably the number and type of cation-oxygen polyhedra. Instead, the jianmuite structure has several features in common with structures of pyrochlore-supergroup minerals, including similarity in unit cell parameters, cubic a ≈ 10 Å and tetragonal a ≈ c ≈ 10 Å in pyrochlore and jianmuite, respectively, and cation packing being cubic I-centred in both structures.