The structural and magnetic phase transitions of Fe-I boracite were studied by optical examns. of the domain structure and by measurements of the spontaneous birefringence using polarized-light microscopy. These phase transitions also were characterized by dielec. and spontaneous polarization studies, realized on ferroelastic/ferroelec. single-domain states, which were obtained by elec. field poling along <100>cub and <111>cub directions, with simultaneous visual control of the domain state. In the trigonal 3m1' phase, an elec. field E‖{111}cub of one polarity produced a monodomain with the spontaneous polarization Ps and the optical axis perpendicular to the (111)cub plane, while that of the reversed polarity gave rise to domains with the three other preferential directions of Ps, noncollinear with E, and to a polarization of Ps/3, indicating the non-180°-reversibility of Ps along <111>cub. The magnetic phase transition 3m1' ↹ m resulted in anomalies both in the dielec. permittivity (up to 2 MHz) and in the spontaneous polarization at the Curie temp. Tc = 31 K. This suggests an interaction between the magnetic moment and the elec. polarization, consistent with the ferroelec./ferroelastic/ferromagnetic coupling effect previously found for the m phase.