The structure of vauxite is characterised by infinite chains parallel to the c crystal axis.[1] One set of chains is built up of octahedra with a ferrous iron ion Fe2+ or an aluminium ion Al in the middle, and an oxygen ion O at each of the six vertices. The central ions of these octahedra are alternately Fe and Al, and adjacent octahedra share edges. At each linked edge two oxygen ions are shared between two octahedra, and each octahedron must have two shared edges to form a chain.