<scp>3D SR</scp> ‐ <scp>μXCT</scp> analysis for lithology detection: Application to Ryugu sample <scp>A0159</scp>

Abstract Extraterrestrial breccia samples are formed through impact‐related processes that combine the fragments of distinct lithologies. As such, they are valuable indicators of the complex formation and evolution history of planetesimals in our solar system. Samples from asteroid (162173) Ryugu, returned to the Earth by the Hayabusa2 mission in December 2020, were characterized as breccias. The boundaries of mineralogical assemblages are typically drawn manually based on interpreted results from specific techniques, mostly performed on artificially produced 2D surfaces. This process inherently introduces subjectivity. Here, we present a semi‐automated analytical method using synchrotron radiation micro X‐ray computed tomography (SR‐μXCT) data, called the Local Histogram method. It enables an unsupervised detection and 3D visualization of a few tens to hundreds of micrometer‐sized lithologies showing sub‐micrometer heterogeneities. We developed the method on a millimeter‐sized Ryugu sample (A0159) in combination with a more traditional global grayscale threshold segmentation. In A0159, we report five distinct lithologies. They were confirmed and further characterized by an additional scanning electron microscopy (SEM) analysis on Xenon plasma‐focused ion beam (Xe‐pFIB) produced sections. Some lithologies show specific relationships with large fractures, while one is particularly enriched in sub‐micrometer sulfides. A0159 is rich in carbonates and hosts the largest millimeter‐scale dolomite vein seen on Ryugu.