The Ca-43 MAS NMR spectra obtained for three calcium silicate glasses containing aluminum and/or sodium are analyzed. The Ca-43 NMR parameters are shown to be highly sensitive to variations in its chemical environment. The transition from a charge-compensating role of [AlO4](-) groups to a network-modifying role near nonbridging oxygen atoms results in an increase of both the isotropic chemical shift and the quadrupolar coupling constant of Ca-43. This effect can be related to the first coordination shell of calcium (through the Ca-O bond distance) which is affected by the chemical environment beyond the first neighbors of calcium. (c) 2007 Elsevier B.V. All rights reserved.