4 DFT calculated isotropic shielding compared to the distortion of its geometric environment. GIPAW NMR calculated 𝛿 !"# versus CSM as defined by ChemEnv . Each coordination environment is broken down into its closest geometric environment and coordination number: Al(IV) sites were classified as tetrahedral, Al(V) sites were subdivided into trigonal bipyramidal and square pyramidal and Al(VI) as octahedral. There are a large number of distorted (CSM > 4) tetrahedral environments, which have a range of 𝛿 !"# shifts.