DISCOVERY OF METEORITIC LAKARGIITE (CaZrO3), A NEW ULTRAREFRCTORY MINERAL FROM THE ACFER 094 CARBONACEOUS CHONDRITE

Introduction: During a nano-mineralogy investigation of the Acfer 094 carbonaceous chondrite, lakargiite (CaZrO3) was identified as submicrometer inclusions in an isolated hibonite grain in section USNM 7233-1. The hibonite grain is described in Simon and Grossman [1]. Lakargiite is a recently found perovskite-group mineral from hightemperature skarns in ignimbrites of the Upper-Chegem volcanic structure, the North Caucasus, Russia [2]. Reported here is the first extraterrestrial occurrence of lakargiite, as a new ultrarefractory mineral in a primitive meteorite, among the first solids formed in the solar system. Field-emission SEM with EDS and electron back-scatter diffraction (EBSD) was used to characterize its composition and structure and associated phases. Occurrence, Chemistry, and Crystallography: Lakargiite [Ca0.95(Zr0.87 Ti0.16)O3] occurs along with tazheranite [(Zr0.52Ti0.18Ca0.16Y0.06Fe0.05 Sc0.03)O1.75], Zr-bearing perovskite [Ca0.94 (Ti0.98Zr0.06)O3] and Os-W-alloy [Os0.81W0.13Fe0.06] as fine-inclusions scattered in the central area of the hibonite [Ca (Al11.70Ti0.14Fe0.10Mg0.06)O19] grain (Fig. 1). Lakargiite appears as irregular or subhedral lath-shaped grains, 300–900 nm in size, sometimes in contact with Os-W or perovskite. Associated tazheranite is a Ca-stabilized cubic zirconia (CSZ), likely being the first reported meteoritic CSZ. EBSD analysis revealed that the lakargiite has a perovskite Pbnm structure, identical to that of synthetic CaZrO3 [3], showing a = 5.591 Å, b = 5.762 Å, c = 8.017 Å, V = 258.3 Å, Z = 4. Origin and Significance: Lakargiite is a new Zr-dominant ultrarefractory mineral, joining the Zr-rich refractory minerals allendeite (Sc4Zr3O12) [4], tazheranite (Scor Ystabilized cubic zirconia) [4, 5] and panguite [6]. Texturally, lakargiite, tazheranite, Zr-bearing perovskite and Os-W formed before host hibonite. Lakargiite is likely an early condensate. Further work is under way to determine its place in the nebula. References: [1] Simon S. B. and Grossman L. 2011. Meteoritics & Planetary Science, in press. [2] Galuskin E. V. et al. 2008. American Mineralogist 93:1903–1910. [3] Koopmanns H. J. A. et al. 1983. Acta Crystallographica Section C 39:1323–1325. [4] Ma C. et al. 2009. Abstract #1402. 40th Lunar and Planetary Science Conference. [5] Ma C. and Rossman G. R. 2008. Geochimica et Cosmochimica Acta 72:12S, A577. [6] Ma C. et al. 2011. Abstract #1276. 42nd Lunar and Planetary Science Conference.