Complex Intergrowths of Non-Stoichiometric Defect-Structured Hibonite and Al-Rich Spinel in an Allende Ca-Al-Rich Inclusion

Han, J ; Ohnishi, I ; Keller, L P

关键词: METEORITIC COMPOSITION;    MINERALS;    STOICHIOMETRY;    ALUMINUM OXIDES;    SPINEL;    CHONDRITES;    CRYSTAL STRUCTURE;    INCLUSIONS;    DEFECTS;    CALCIUM COMPOUNDS;    ALLENDE METEORITE;    MICROSTRUCTURE;    TRANSMISSION ELECTRON MICROSCOPY;   

RP-ID  :  JSC-E-DAA-TN69157

美国|英语

来源: NASA Technical Reports Server

【 摘 要 】

Hibonite is a primary ultra-refractory mineral occurring in many Ca-Al-rich inclusions (CAIs) and is predicted to condense as the second major phase from a cooling gas of solar composition. Our previous microstructural studies of hibonite in carbonaceous chondrites revealed its unique microstructures consisting of numerous defects that contain Mg-enriched, wider spinel blocks in stoichiometric hibonite. Han, J. et al. [2 items] demonstrated experimentally that defect-structured hibonites can grow easily in the presence of minor Mg and are kinetically more stable than equilibrium assemblages predicted by thermodynamic calculations. However, a thermo-dynamic vs. structural stability of defect-structured hibonite relative to other early-condensed Al-rich phases such as corundum, grossite, and spinel remains poorly constrained. Here, we present the results of atomic resolution TEM (Transmission Electron Microscopy) imaging of hibonite in a compact Type A CAI in the Allende CV3 chondrite in order to better understand the crystal structure and chemistry of defect-structured hibonite and its associated Al-rich phases, especially non-stoichiometric, Al-rich spinel, in the context of the formation of first refractory solids in the early solar nebula.