The Mineralogy of a Rhönite‐bearing Calcium Aluminum Rich Inclusion in the Allende Meteorite

The meteoritic occurrence of rhönite‐bearing calcium and aluminum rich inclusions (CAIs) appears to be restricted to the Allende meteorite. These inclusions, however, are very scarce as only four are known to the author. This report is primarily concerned with the descriptive mineralogy of one of these rare CAIs. The inclusion contains, in decreasing order of abundance, melilite (Ak15‐Ak55), spinel, fassaite, rhönite, perovskite, grossular, Ni‐Fe metal, hibonite, troilite, a vanadium‐iron oxide (20–27 wt % V2O3), molybdenite, geikielo‐ilmenite and magnetite. Although this mineral assemblage formed under nonequilibrium conditions from a molten drop, the coarse grained texture does not indicate rapid crystallization. Local chemistries evidently played a significant role in the formation of metastable phase relationships and symplectites, thereby confounding the construction of a plausible thermal history for this CAI.