Once principle quantum number n equals 3 or greater, angular quantum number can equal 2. When angular quantum number l=2, it is considered the d-orbital. For the d-orbital, the magnetic quantum number ml can equal -2 to 2, taking the possible values -2, -1, 0, 1, or 2. This gives rise to five d orbitals, dxy, dyz, dxz, dx2-y2, and dz2. The magnetic quantum numbers do not correlate to a specific orbital, rather the orbitals are a linear combination of the different ml values, similar to that of the px and py orbitals. The general shape of the d-orbitals can be described as "daisy-like" or "four leaf clover" with the exception of the the dz2 orbital which looks like the donut with a lobe above and below. All the d-orbitals contain 2 angular nodes. In the case of dxy, dyz, dxz, and dx2-y2 they are planar angular nodes, easily seen as the axes which bisect the lobes of the orbitals. In dz2 they are conical angular nodes which divide the "donut" part of the orbital with the upper and lower lobes. The d-orbitals are important in the transition metals because they are typically what are used in bonding. Crystal Field Theory, more specifically Crystal Field Splitting, uses the d-orbitals and their degeneracy to describe spectroscopic properties of transition metal complexes.