Chapter 3 Diagenetic Transformations of Minerals As Exemplified By Zeolites and Silica Minerals-A Japanese View

Publisher Summary This chapter examines the diagenetic transformations of minerals as exemplified by zeolites and silica minerals. Japan is one of excellent localities in the world to study the occurrence and genesis of natural zeolites, because volcanic glass of varying composition that is the best raw material of zeolites occurs widely in volcaniclastic rocks of younger geologic ages. Zeolites originate from many kinds of precursor minerals, such as volcanic glass, impact glass, non-crystalline and crystalline clays, feldspar, feldspathoid, and even zeolite itself. Water is indispensable to zeolites so that the geologic occurrence of zeolites can best be classified based on the states of interstitial water in zeolitic rocks. Much work in the field and in laboratories has proved that temperature is a major factor in controlling zeolite formation. Chemistry of pore water plays another important role of zeolite formation. As a result of the presence of a geothermal or chemical gradient, zeolites commonly occur in a vertically or laterally zoned arrangement, which is commonly mappable as zeolite zones.