The principal spontaneous birefringence ΔnS(γ, α) of the trigonal ferroelec.-ferroelastic phase was measured at 5-468 K (λ = 489, 666 nm) and the dielec. const. ε33 of the same phase at 5-300 K (f = 100 kHz). The spontaneous polarization PS of the trigonal and monoclinic ferromagnetic phase was measured at 5-468 K. At the onset of the monoclinic phase at ∼11 K, PS undergoes a drastic change of slope which can be attributed to an order-parameter and magnetization-induced polarization. The spontaneous Faraday rotation in the ferromagnetic phase was measured vs. temp. at λ = 539 nm.