Figure F26. X-ray diffractogram traces of samples from lithologic Unit IV. Clay = nonbasal clay mineral reflection; Qz = quartz; CT = opal-CT; and Cc = calcite. Samples are from background carbonate sediments. Diffractograms from the other major lithology of Unit IV, which is chert and porcelanite, are not shown here. Note presence of opal-CT along with quartz and calcite in Sample 185-1149B-18R-1, 9-11 cm. Also note that individual diffractograms are offset vertically for clarity.