What makes the chert bedded?
The prominent bedding seen in Franciscan chert leads to the name ribbon chert. The hard, silica-rich chert beds are separated by thin beds of soft, clay-rich shale. These dramatically alternating beds are the result of a process called diagenetic enhancement. When the chert-forming sediments were laid down, some levels had slightly more silica than others. When the sediments were transformed into rock in a process called diagenesis, the silica in the less silica-rich zones migrated into the more silica-rich zones, increasing the silica contrast between the levels and enhancing the bedding to form ribbon chert.
