Using the Mossbauer effect of Fe 57 , ferrous compounds have been investigated systematically in order to elucidate their magnetic properties from an atomic point of view. Parameters of isomer shifts, quadrupole interactions and internal magnetic fields at the iron nuclei at various temperatures are listed in Table I. It should be noticed that the ratio of eq z (FeSiF 6 ·6H 2 O)/eq z (FeCO 3 ) is -1.8, where eq z is the electric field gradient parallel to the c axis of each crystal. This indicates that the ground state of FeCO 3 is an orbital doublet. Some forbidden lines were observed in Fe 3 (PO 4 ) 2 ·8H 2 O and FeC 2 O 4 ·2H 2 O because of the existence of the maximum electric field gradient tensor being perpendicular to the internal magnetic field.