The Winchcombe meteorite—A regolith breccia from a rubble pile
 CM
 chondrite asteroid

– The Winchcombe meteorite is a CM chondrite breccia composed of eight distinct lithological units plus a cataclastic matrix. The degree of aqueous alteration varies between intensely altered CM2.0 and moderately altered CM2.6. Although no lithology dominates, three heavily altered rock types (CM2.1 – 2.3) represent > 70 area%. Tochilinite – cronstedtite intergrowths (TCIs) are common in several lithologies. Their compositions can vary signiﬁcantly, even within a single lithology, which can prevent a clear assessment of alteration extent if only TCI composition is considered. We suggest that this is due to early alteration under localized geochemical microenvironments creating a diversity of compositions and because later reprocessing was incomplete, leaving a record of the parent body’s ﬂuid history. In Winchcombe, the fragments of primary accretionary rock are held within a cataclastic matrix ( ~ 15 area%). This material is impact-derived fallback debris. Its grain size and texture suggest that the disruption of the original parent asteroid responded by intergranular fracture