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  1. This report documents the results of X-ray diffraction analyses of 132 mud and mudstone samples collected offshore Sumatra during International Ocean Discovery Program Expedition 362. The clay-size mineral assemblage consists of smectite, illite, chlorite, kaolinite, and quartz. The relative abundance of smectite at Site U1480 decreases downsection from a mean value of 33 wt% in Unit I to a mean of 19 wt% in Unit II; illite increases from a mean of 49 wt% to a mean of 59 wt%. Smectite in Unit III increases to a mean of 73 wt%, and illite decreases to a mean of 19 wt%. Mean values are subordinate (<16 wt%) for undifferentiated chlorite + kaolinite and <7 wt% for quartz in all units. A significant compositional discrepancy occurs between Subunit IIIA at Site U1480 (mean smectite = 64 wt%) and Unit III at Site U1481 (mean smectite = 36 wt%). At Site U1480, the expandability of illite/smectite mixed-layer clays increases downsection, which is opposite to the trend expected with burial diagenesis. The maximum value is 88% within smectite-rich samples from Unit III. Values of the illite crystallinity index are between 0.42Δ°2θ and 0.76Δ°2θ, with most data straddling the generic boundary between advanced diagenesis andmore »anchimetamorphism. Illite (060) reflections yield bo values of 8.988 to 9.000, which are indicative of low phengite contents. Smectite (060) reflections display peak apex positions of 61.998°–61.798°2θ, which are consistent with the mineral structure of montmorillonite. The detrital illite fraction contains 46%–60% 2M1 polytype, and the remainder is 1M/1Md.« less