Summary: The crystal structure of galeite from Searles Lake (California) has been determined by means of X-ray diffraction data on a single crystal. A possible structure was derived from that of schairerite on the basis of chemical and lattice analogies and was confirmed by comparison of the observed diffractometric structure factors with the calculated ones. The refinement was performed by least-squares methods employing isotropic thermal parameters and assuming that atoms related by translational pseudosymmetry exhibit equal thermal parameters. The final R value is 0·09. The cell content is 3[Na₁₅(SO₄)₅F₄Cl]; the space group is P31m The lattice dimensions are a 12·197(4)Å, c 13·955(10) Å The marked subcell has P3m1 symmetry and a 7·042Å, c 13·955 Å. The crystal structure of galeite consists of a three-dimensional framework, formed by coordination octahedra around Na⁺ ions, including tetrahedral holes with sulphur atoms at the centres. The three-dimensional framework can be considered built up by five octahedral sheets (seven sheets can be recognized in schairerite and six in sulphohalite). The very close analogies occurring in the structures of galeite and schairerite are discussed.