The transformation of aragonite to calcite (A–C) is an irreversible reconstructive transformation involving a change from 6 to 9 in the primary coordination. Cationic impurities like Na+, Mg2+, Zn2+, Y3+, La3+, Nd3+, Gd3+, Dy3+have been doped in pure aragonite and their effect on the kinetics and energetics of its transformation to calcite is studied. By employing a DTA technique, the enthalpy and energy of activation for the transformation have been calculated. The ir spectra of aragonite and calcite in pure form and with various impurities have been studied and the effect of impurities on absorption bands discussed.