Uniform dispersions of magnesium fluoride particles of different morphologies were prepared by precipitation in aqueous solutions. The resulting cubic, prismatic, and platelet-like nanosize solids had single crystal structure with X-ray pattern characteristic of the mineral sellaite. In contrast, two kinds of polycrystalline MgF2 spheres were obtained by aggregation of the nanosize subunits. The mechanisms of the formation of the resulting particles of different shapes are explained by the role of the pH and ionic strength. In addition, for prospective numerical modeling the surface tension of spherical and platelet particles of MgF2 was evaluated from the X-ray data by a lattice parameter change method.