Observation of “hidden” magnesium: First-principles calculations and 25Mg solid-state NMR of enstatite

► 25-Mg solid-state NMR of enstatite (MgSiO3) polymorphs. ► MAS NMR spectra exhibit one resonance rather than the two expected. ► DFT calculations predict a large quadrupolar coupling for the “hidden” site. ► Observed experimentally using frequency-stepped CPMG experiments. ► Investigate the origin of the differences using a point charge model.