Pseudogaylussiet in het Nederlandse en Duitse kustgebied

This paper deals with the occurrence of so-called pseudogaylussite in the coastal areas of the Netherlands and Germany. It consists of calcite and is found as separate crystals and as calcareous concretions, both at a depth of a few meters in holocene marine clay deposits. The literature on this subject is reviewed and some specimens, which were found some years ago in the province of Friesland, are described. The original mineral of this calcite pseudomorph is supposed to be gaylussite, but it is actually unknown. The recently discovered mineral ikaite is not likely to be the parent substance, at least in this case. Further investigation is necessary.