Saturation Degree of the Aral Sea in CaF2 in the Modern Period

The F concentrations are determined in water from residual basins of the modern Aral Sea (Small Aral Sea, Lake Tshchebas, western basin of the Large Aral Sea, and Chernyshev Bay) in natural state and in equilibrium with CaF2 (mineral fluorite). The saturation of the Aral waters in CaF2 with salinity of 86–153 g/L determined for the first time allows possible chemogenic precipitation of fluorite. Further increase in salinity up to 306 g/L makes this process impossible due to the increasing excess in F concentration equilibrated with CaF2 over its natural content.