Symmetry of SO4 Ion in Gypsum

The statement 1 “that the SO 4 ion in gypsum has only an axis of two-fold symmetry” is misleading and the new findings on symmetry should be restated. With the new parameters that we have found for it in gypsum the SO 4 ion, considered in isolation, forms a sphenoid in the point group (tetragonal bisphenoidal) and not a tetrahedron in the point group (hexatetrahedral). In the gypsum structure it still conforms to the point group 2 (monoclinic sphenoidal).