The Ca chemical shifts of the different Ca sites are presented as the mean value. The Ca NMR spectrum of each calcium site was modeled as a normal distribution with the mean value (as µ) defining the center of the distribution and the typical full width at half maximum (FWHM as σ ) controlling the width. FWHM was chosen as 5.2 ppm. This is the FWHM of 60% enriched calcium benzoate trihydrate Ca MAS NMR spectra . Comparable FWHM are reported for natural abundance Ca MAS NMR spectra of calcium carbonate .