Summary: Preliminary work has been done on the structure of the mineral bredigite, and it has been shown that while the structure is similar to, it is not identical with, that of β-K₂SO₄. The X-ray investigation has shown the presence in some bredigite crystals of a small quantity of a trigonal phase which could not be detected optically. The optic axial plane, twin planes, and cleavage plane have been determined unambiguously. The relative orientations of the trigonal, orthorhombic, and monoclinic phases are discussed in relation to their structures.