Ultramorphology of Deep Sea Cristobalitic Chert

X-RAY diffraction studies by Rex1,2, Calvert3 and others identify alpha-cristobalite as one of the chief constituents of post-Cretaceous deep sea cherts. Older cherts are quartz-rich and experimental and petrographic investigations4,5 suggest that quartz cherts are the end product of the reactions: bio-genous opal→cristobalite→quartz chert. It is, however, not clear whether these reactions are solid state or solution/reprecipitation conversions. Also, recent field and mineralogical evidence6,7 suggests that volcanism rather than purely bio-genous production may be an important source of silica for the extensive mid-Cainozoic cristobalitic cherts of the Caribbean and North Atlantic Ocean basins.