Figure F25. Thin section photomicrographs of a zoned chert nodule from the Aptian section (Sample 198-1207B-37R-CC, 25-27 cm). This is a higher magnification view of the contact between chert (left) and porcellanite (right). Radiolarians are filled with tan, isotropic opal. Note how carbonate and other impurities in the porcellanite groundmass help define tests of radiolarians and how these tests become "ghosts" in the chertified portion of the sample. The upper view is under plane-polarized light, whereas the lower view is with nicols crossed.

Figure F25. Thin section photomicrographs of a zoned chert nodule from the Aptian section (Sample 198-1207B-37R-CC, 25-27 cm). This is a higher magnification view of the contact between chert (left) and porcellanite (right). Radiolarians are filled with tan, isotropic opal. Note how carbonate and other impurities in the porcellanite groundmass help define tests of radiolarians and how these tests become "ghosts" in the chertified portion of the sample. The upper view is under plane-polarized light, whereas the lower view is with nicols crossed.