Dawsonite, alumohydrocalcite, nordstrandite and gorceixite in Permian marine strata of the Sydney Basin, Australia

Dawsonite, alumohydrocalcite, nordstrandite, gorceixite and calcite are associated in marine strata of the Permian Shoalhaven Group of the Sydney Basin, south-eastern Australia. The assemblages were apparently of late syngenetic or epigenetic development and resulted from two interrelated processes: (a) precipitation from solutions rich in sodium, aluminate and carbonate ions and (b) reaction of these solutions with earlier-formed minerals leading to the development of complete and partial pseudomorphs. Although the evidence is inconclusive, the host rocks were probably the source of the ions.