Chemical and Petrologic Evidence of Extensive and Complex Aqueous Alteration of Cr Gra

Introduction: Although some CR chondrites are recognized to be among the most pristine meteorites [1], other members of this group are heavily hydrated [e.g. 2]. However, no evidence of thermal metamorphism has been documented for this group. Antarctic fall GRA 06100, initially classified as a CR2 chondrite have not been previously studied. We use optical microscopy, SEM, and focused beam EPMA to study GRA 06100, in order to shed light on the advanced stages of alteration history in the CR parent body. Results: Two petrographic thin sections were prepared from sample GRA 06100.6. Although GRA 06100 has been assigned weathering type B, neither section shows significant signs of terrestrial alteration, such as rust staining or networks of ferryhydrite veins. Therefore, we suggest that the bulk of the aqueous alteration recorded by this meteorite is not terrestrial.