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Abstract
Breccias are the most common rock type found on the lunar surface, and make up the majority (~95%) of known lunar meteorite samples (Korotev & Irving, 2021). Breccias are a complex assemblage of lithified aggregates of clastic debris and melt that formed via impacts on the lunar surface (including impact gardening), a process that causes the mixing, melting, and sintering of material from the upper lunar crust and regolith into heterogeneous rock (Arai et al., 2008; Heiken et al., 1991). A clast’s lithology and chemical composition provide direct constraints on the petrogenesis of the rock fragment. The lack of a unified classification scheme for clasts within lunar breccias, however, makes the comparison of clast lithologies between different breccias challenging. An internally consistent classification scheme would allow observations of new samples to be directly comparable. This would lead to more uniform comparisons between clasts, their components, and allow stronger interpretations of their petrogenesis and direct comparisons of the geologic settings that these breccias record. The goal of this study is to develop such a scheme for clasts within lunar breccias for the broader community. Such comparisons can already be made, but with an internally consistent classification of clasts, the comparisons would be more robust, and results would be comparable between different researchers. The proposed classification scheme presented here was built by integrating and streamlining published lunar rock classification schemes into a single scheme that is specialized for identifying clasts within lunar breccias. This classification scheme was verified by applying it to three lunar breccia meteorite samples.
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