Figure F20. Thin section photomicrographs of the rim of a chert fragment recovered within soupy white Campanian ooze (Sample 198-1207A-24X-5, 4-5 cm). The speckled appearance is due to circular white blebs of microquartz embedded within a tan opal matrix/cement. Under crossed nicols (not shown here) the white circular features exhibit some birefringence, whereas the surrounding tan "cement" is isotropic. At higher magnification (lower view), some of the blebs exhibit "doughnut" shapes, suggesting that they may be silicified coccoliths. The percent of opaline groundmass is high (~50%), similar to the porosity estimates for surrounding unconsolidated nannofossil ooze. Note the presence of a silicified foraminifer (chambers in center) and thin quartz lenses of uncertain origin. Both views are under plane-polarized light.