The new mineral tomiolloite, Al12(Te4+O3)5[(SO3)0.5(SO4)0.5](OH)24: A unique microporous tellurite structure

Abstract

Abstract Tomiolloite (IMA2021-019) is a new aluminum tellurite sulfite-sulfate mineral discovered at the Bambolla mine, Moctezuma, Sonora, Mexico, a well-known tellurium (Te) mineral locality. Tomiolloite forms roughly spherical clusters of crystals comprised of very thin, needle-like crystals (1 μm diameter, ~40 μm length) around a core of small, stubbier, broken crystals. Tomiolloite is generally found growing on tellurite or quartz. The strongest powder X-ray diffraction lines are [dobs Å (Iobs) (hkl)]: 11.667 (89) (100), 8.240 (38) (101), 4.107 (29) (202,211,121), 3.223 (100) (203,302,130), and 2.905 (37) (213,123,222,400). The empirical formula of tomiolloite, as determined by electron microprobe analysis, is (Al10.64Te1.016+Fe0.313+Zn0.04)Σ12(Te5.004+Pb0.02)Σ5.02(S0.494+S0.496+Si0.02)Σ1.00O21.53[(OH)20.86Cl0.11]Σ20.97, which is simplified to the ideal formula Al12(Te4+O3)5[(SO3)0.5(SO4)0.5](OH)24. Significant Te6+ substitution for Al3+ is observed in tomiolloite, verified by X-ray photoelectron spectroscopy and crystal-structure analysis. The structure of tomiolloite was determined using synchrotron single-crystal X-ray diffraction, showing that tomiolloite is hexagonal and crystallizes in the space-group P63/m, with the unit-cell parameters a = 13.3360(19) Å, c = 11.604(2) Å, V = 1787.3(6) Å3, and Z = 2. Tomiolloite has a unique microporous framework structure, which bears a slight similarity to that of zemannite, but it has a much larger cavity diameter (8.85 Å). The framework is built from edge-sharing Mφ6 octahedra (M = Al3+ and Te6+), Te4+O3 trigonal pyramids, and Te4+O4 disphenoids. Mφ6 octahedra edge-share to form crankshaft-shaped chains along c, with Te4+On polyhedra filling notches in the crankshafts and providing linkages between adjacent chains. The framework has an overall positive charge, which is balanced by the presence of both sulfite (SO32−) trigonal pyramids and sulfate (SO42−) tetrahedra in the channels.