The degree of polymerization of a mineral is determined by the number of oxygens per TO4 tetrahedron that are shared with adjacent TO4 tetrahedra. The simplest case is when NO oxygens are shared with adjacent tetrahedra. The next group of minerals have TO4 tetrahedra that share one oxygen with an adjacent tetrahedron to form T2O7 dimers as shown in the diagram at left. There are also a number of minerals that contain both TO4 monomers and T2O7 dimers. TO4 tetrahedra that share two oxygens with adjacent tetrahedra can have either rings of TO4 tetrahedra or chains of tetrahedra.
Examples are tourmaline and axinite.
The diagram at the right shows that the chains can be either single or double. Common minerals with the single chain structure include the pyroxene group minerals and the pyroxenoid group minerals. Minerals with linked double chains are in the amphibole group. When the TO4 tetrahedra share three oxygens with adjacent tetrahedra, a sheet structure is formed. The drawings at left show a top view of a T2O5 sheet.