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 Tschauner1,2, Beckett JR1Rossman GR1, Liu W3

1Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena 91125-2500, U.S.A.

2High Pressure Science and Engineering Center and Department of Geoscience
University of Nevada, Las Vegas, NV 89154, USA

3Advanced Photon Source, Argonne National Laboratory, Chicago, IL 60439, USA

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 [(Ti0.79Zr0.16Si0.04)4+Σ0.99(Sc0.20Al0.20Y0.07V0.02Cr0.01)3+Σ0.50(Mg0.18Ca0.08Fe0.03)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) , b = 9.778(2) , and c = 9.815(1) , yielding V = 938.7(1) 3, 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.

Panguite
SEM image of panguite. Image Credit: Chi Ma