Replication Data for: Classification of CM chondrite breccias – Implications for the evaluation of samples from the OSIRIS REx and Hayabusa 2 missions.

Key Points: • CM Chondrites as Breccias: CM chondrites are complex impact breccias, primarily consisting of different lithic clasts exhibiting various degrees of aqueous alteration. • Investigation of Clasts: The study analyzed the degree of alteration in individual clasts within 19 CM chondrites and CM-like clasts in three achondrites, focusing on the chemical analysis of tochilinite-cronstedtite intergrowths (TCIs). • Methodology: Identification of TCIs in various chondritic lithologies was performed using backscattered electron (BSE) images of polished thin sections, followed by electron microprobe measurements for classification. • Subclassifying CM Chondrites: The study proposes an extended classification scheme based on Rubin's scale (CM2.0-CM2.9), with a focus on the "FeO"/SiO2 ratio in TCI chemistry, while considering brecciation and the degree of alteration of individual clasts. • Implications for Future Missions: The findings will be significant for interpreting samples returned from the OSIRIS-REx and Hayabusa 2 missions, given the range of aqueous alteration and mixing of clasts with different alteration histories in CM chondrites.