Petrology and classification of A‐9003, A 09535, and Y‐82094: A new type of carbonaceous chondrite

Most carbonaceous (C) chondrites are classified into eight major groups: CI, CM, CO, CV, CK, CR, CH, and CB. However, some are ungrouped. We studied two such chondrites, Asuka (A)-9003 and A 09535. The abundance of chondrules and matrix and chondrule sizes in these meteorites are similar to those in ordinary chondrites and unlike any known carbonaceous chondrite group. In contrast, they contain 4–6 vol% of refractory inclusions and have oxygen isotopic compositions within the range of CO and CV chondrites. Therefore, A-9003 and A 09535 are classified as C chondrites. Petrologic subtypes of A-9003 and A 09535 are 3.2. All these features closely resemble those of another ungrouped chondrite, Yamato (Y)-82094, and differ from those of any C chondrites reported by now. A-9003, A 09535, and Y-82094 likely represent a new type of C chondrite. We provisionally call them CA chondrite after Asuka in Antarctica. Our study suggests a wider range of formation conditions for C chondrites than currently recorded by the major C chondrite groups