Panguite, (Ti⁴⁺,Sc,Al,Mg,Zr,Ca)_1.8O₃, a new ultra-refractory titania mineral from the Allende meteorite: Synchrotron micro-diffraction and EBSD

Ma C¹, Oliver Tschauner^1,2, Beckett JR¹, Rossman GR¹, Liu W³

Abstract

Panguite (IMA 2010-057), (Ti⁴⁺,Sc,Al,Mg,Zr,Ca)_1.8O₃, is a new titania, occurring as fine-grained crystals with Ti-rich davisite in an ultra-refractory inclusion within an amoeboid olivine inclusion from the Allende CV3 carbonaceous chondrite. The phase was characterized by SEM, EBSD, synchrotron micro-diffraction, micro-Raman and EPMA. The mean chemical composition of the type panguite is (wt%) TiO₂ 47.97, ZrO₂ 14.61, Sc₂O₃ 10.67, Al₂O₃ 7.58, MgO 5.54, Y₂O₃ 5.38, CaO 3.34, SiO₂ 1.89, FeO 1.81, V₂O₃ 0.95, Cr₂O₃ 0.54, HfO₂ 0.28, sum 100.55 with a corresponding empirical formula calculated on the basis of 3 O atoms of [(Ti_0.79Zr_0.16S_i0.04)⁴⁺_Σ0.99(Sc_0.20Al_0.20Y_0.07V_0.02Cr_0.01)³⁺_Σ0.50(Mg_0.18Ca_0.08Fe_0.03)²⁺_Σ0.29]_Σ1.78O₃. Synchrotron micro-Laue diffraction (i.e., an energy scan by a high flux X-ray monochromatic beam and white beam diffraction) on one type domain at sub-micrometer resolution revealed that panguite is an orthorhombic mineral in space group Pbca. The structure is a subgroup of the Ia3 bixbyite-type. The cell parameters are a = 9.781(1) Å, b = 9.778(2) Å, and c = 9.815(1) Å, yielding V = 938.7(1) ų, Z = 16 and a calculated density of 3.746 g/cm³. Panguite is not only a new titania mineral, but also a new material, likely formed by condensation. It is one of the oldest minerals in the solar system.

SEM image of panguite. Image Credit: Chi Ma