The solubility of crystalline and precipitated calcium fluoride in seawater and brines of the first stages of its evaporative concentration (before the beginning of gypsum and halite setting) was experimentally studied. It was established that in the entire studied range of salinity, seawater and its derivatives are strongly undersaturated by the calcium fluoride, which excludes its spontaneous precipitation in drying isolated sea basins. A necessary condition for the formation of sedimentary fluorite is the entry into the drying sea basins of significant amounts of dissolved fluorine from external sources, which can be river runoff, volcanic emanations, and hydrothermal solutions.