ABSTRACTHolocene dolomite forms in the sediment of Lake Hayward, a small permanent hypersaline lake in the Clifton‐Preston Lakeland System, Western Australia. The geomorphological setting of dolomite formation in Lake Hayward is similar to the Coorong region in South Australia. Unlike in the Coorong region, dolomite in Lake Hayward does not form as a direct precipitate from the lake water, but is of diagenetic origin. This can be deduced from the following features: (1) the dolomite occurs only below 60–70 cm from the sediment‐water interface, (2) dolomite occurs as luminescing cement, and (3) dolomite has pristine well‐formed rhomb‐shaped crystals. The source of magnesium for dolomitization is probably from the concentration on inflowing groundwater by evaporation and the selective removal of calcium by chemical and biological aragonite/calcite prec