The principal building blocks are also described as intermediate-range order. These blocks are composed of subunits, identified by the short-range order of a few atoms and characterized by bond lengths, bond angles (next-nearest neighbor distances), and site geometry. Intermediate-range order describes third neighbor distances, dihedral angles, atomic ring structures, and local topology. It distinguishes for tetra-, tri-, and divalent bonding truly three-dimensional (tetrahedral), two-dimensional (layer-like), and one-dimensional (chain-like) structures, respectively.