This data publication uses XRD bulk rock analyses carried out on cuttings aboard D/V Chikyu during the International Ocean Discovery Program (IODP) Expeditions 338 and 348 of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) project (Strasser et al, 2014, Tobin et al., 2015). More data on clay minerals in the C0002F and C0002P holes are published by Underwood and Song (2016a and 2016b), and Underwood (2017). These data are supplementary material for Schleicher and Jurado (2019). XRD data of the clay size fraction were analyzed at the University of Michigan, USA, and the GFZ Potsdam, Germany. All XRD analyses of the random powder and texture (oriented) preparation followed the analytical methods described in Moore and Reynolds (1997). Oriented clay size samples were measured under air-dried and glycolated conditions, the latter treatment caused interlayer expansion of swelling clays, allowing the recognition of discrete smectite and mixed-layer smectitic phases. In order to compare the clay mineral content, and the mineral amount relative to the adjacent material, exactly 45 μg of the material was mixed with 1.5 ml deionized water and dropped on a round glass slide (diameter 32 mm). All air-dried samples were measured at a relative humidity (RH) of ~30%, and afterward stored in a desiccator filled with ethylene glycol, in order to investigate the final swelling stage of the smectitic phases. The data are provided as tab delimited table (2019-002_Schleicher-Jurado_XRD-data.txt, see also Table 1 in Schleicher and Jurado, 2019) with the following columns:- Hole: name of the C0002 subhole- Depth (mbsf): depth in meter below surface (mbsf)- Sample (SMW): sample number SMW (solid cuttings taken from drilling mud)- Smectite (int./cps): intensity of smectite in counts per second (cps)- Illite (int./cps): intensity of smectite in counts per second (cps) In addition, the original XRD measurements are provided in raw and text formats (2019-002_Schleicher-Jurado_original-XRD-measurements.zip). All science data from these expeditions are also accesible via the Database of the science data acquired by International Ocean Discovery Program and Integrated Ocean Drilling Program expeditions of D/V Chikyu (http://sio7.jamstec.go.jp/).