ABSTRACT

Barium-feldspar, hyalophane, is reported from Lower Ordovician shales of the Oslo Region. The feldspars occur in beds with pseudomorphs after barite which now are replaced by quartz, calcite, pyrite and feldspar. It is concluded that diagenesis or weak metamorphism under reducing conditions, due to the presence of organic carbon, has dissolved the barite. Simultaneous growth of feldspar has therefore taken place in an environment with high Ba/K ratio leading to the crystallization of hyalophane.