R5: Extraterrestrial materials

[R5-03] FIB-TEM observation of co-existing tridymite polymorphs in Moama meteorite

*Atsushi Takenouchi¹, Yohei Igami², Akira Miyake², Norimasa Shimobayashi², Takashi Mikouchi³, Haruka Ono³ (1. Kyoto Univ. Museum, 2. Kyoto Univ., 3. The Univ. of Tokyo, Univ. Museum)

Keywords:Silica, tridymite, TEM, thermal metamorphism

Meteorites sometimes contain various combinations of silica polymorphs, and their variations may relate to their thermal metamorphic history. Here, we report the results of the FIB-TEM study focusing on co-existing tridymite polymorphs in Moama eucrite to clarify the occurrence of the polymorphs. Our observation revealed that monoclinic (Aa) and pseudo-orthorhombic tridymite shared their (001) planes, indicating that they were formed by transformation from a single high-temperature tridymite grain.