Crystallization process of chalcedony and agate in Japan

Abstract

We discuss about precipitation processes of chalcedony and agate precipitation on the basis of textures and occurrence. Textures of chalcedony and agate are grouped to four types, the variation of texture is caused by replacement processes after opal-A, opal-CT and silica polymorphs. In our observations of fine texture, there has been no evidence that chalcedony direct precipitates from solution.  Most chalcedony and agate from Japan were produced by replacing opal-CT and opal-A, and textures of chalcedony and agate are pseudomorphs after these phases.