Plate 4d.: Calcite-cemented veinlets in opal-CT porcelanite, Arroyo Burro Beach. Seams of host rock outline the margin of the central horizontal vein, indicative of crack-seal vein formation. Vein contact at lower left is lined with bitumen, largely removed during sample preparation and replaced by epoxy. Bitumen suggests that last crack-opening increment was invaded by bitumen before calcite cementation could occur. FOV 3 mm, vertical section, plane-polarized light