Cristobalite inclusions in the Tatahouine achondrite: Implications for shock conditions
The mineralogy of the Tatahouine diogenite was investigated by optical microscopy, Raman micro-spectrometry, and scanning and transmission electron microscopies. Inclusions of alpha-cristobalite in orthopyroxenes, locally in symplectic association with chromites. or associated with metal, have been characterized for the first time in a diogenite. Mosaicism of the orthopyroxenes indicates shock effects in the meteorite. The shock history of the meteorite must be consistent with the presence of vein-like structures containing inclusions of well-crystallized cristobalite, it low-pressure, high-temperature phase. Several possible mechanisms to account for these observations are discussed. The simplest one, consistent with all observations, is that a shock event would have occurred in it hot orthopyroxenite, either before extensive cooling of the asteroid, or in materials heated by previous impacts and maintained hot under an ejecta blanket.