Conditions for the Formation of Sellaite in Salt Sediments

The conditions for magnesium fluoride (sellaite) precipitation from seawater with a salinity of 35–105‰ were experimentally determined. It was found that the precipitation of MgF 2 at the salinity of 35, 70, and 105‰ occurs at a concentration of dissolved fluorine above 37, 46, and 51 mg/L, respectively. In isolated evaporite basins, the fluorine concentration required for the formation of sellaite is not reached at all stages of the evaporative thickening of seawater. Therefore, it is assumed that a high concentration of fluorine, sufficient for the precipitation of sellaite, arises as a result of the combined effect of evaporation and additional input of this element into salt-bearing basins with river runoff and/or the release of coprecipitated and sorbed fluorine during the post-sedimentary recrystallization of salt minerals.