We assembled a new set of standard mineral mixtures for XRD analysis of bulk powders from Nankai Trough using the SVD method and the Scintag diffractometer at the University of Missouri. The new normalization factors are more accurate than the factors used during shipboard analyses during Leg 190. They result in a systematic increase (by an average of ~6 wt%) in estimates of total clay in bulk powders, whereas values for quartz decrease by an average of 8 wt%. We also assembled a set of standard mineral mixtures for oriented clay-sized aggregates (smectite + illite + chlorite + quartz). Estimates of relative mineral abundance based on SVD normalization factors are considerably more accurate than estimates based on Biscaye (1965) peak area weighting factors. Regardless of which method is used, core samples from DSDP Site 297 show significant increases of smectite within the lower part of the Shikoku Basin. Percentages of smectite within the bulk sediment are typically >30 wt% within the lower part of the turbidite facies and within the volcaniclastic-rich facies.