Key Points:</br> • <b>CM Chondrites as Breccias</b>: CM chondrites are complex impact breccias, primarily consisting of different lithic clasts exhibiting various degrees of aqueous alteration.</br> • <b> Investigation of Clasts</b>: 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).</br> • <b>Methodology</b>: 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.</br> • <b>Subclassifying CM Chondrites</b>: 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.</br> • <b>Implications for Future Missions</b>: 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.