The electric field gradient (Y-=) has been measured at the Mg, Sr and Ba sites in MgCO3 SrCO3 and BaCO3 by nuclear magnetic resonance. These measurements. along with the results of Dupree et al. for the Y-= at the Ca site in the calcite and aragonite forms of CaCO3, have been compared with ab initio electronic structure calculations using the density functional based code for crystalline solids, WIEN 97. The agreement between the theoretical and experimental values of Y-= is found to be within 10%. (C) 2002 Published by Elsevier Science B.V.