When ancient seas dried up, they deposited their mineral contents as sedimentary deposits. Geologica restricts the occurrence of these to plains, deserts and wastelands. There are three layers in every deposit. From bottom up, these are: limestone, gypsum and rock salt (see pictures below). The limestone formed the original sea floor, and the gypsum and rock salt crystallized on top of it. About 5% of the gypsum is concentrated celestine.
An evaporite deposit undergoing excavation, with rock salt, gypsum, and limestone layers, coincidentally inter-mixed coal and mudstone. Celestine is also visible.