Single-crystal photographs of hauyne from the Eifel district showed beside the cubic reflections of the space group P [unk]3 n numerous additional ones which can be interpreted as reflections of a superstructure. They show a rod-like distribution along [110] directions in the reciprocal lattice. Beside these reflections diffuse blackening of the films is visible along the same directions. This indicates an additional one-dimensional disorder. The reflections of the superstructure do not disappear on heating, but in the range between 1000–1100°C a rearrangement of these reflections occurs. Some hauyne from Vesuvius shows no superstructure. Fourier syntheses of the hauyne with and without superstructures provide evidence that the superstructure is called forth by SO 4 groups and by a part of the (Ca, Na) ions.