The microstructure and crystallographic orientation relationship of CaF₂–MgO eutectics produced for the first time were characterized by electron microscopy. The eutectic contains single-crystal MgO rods (∼0.7 μm in size, spaced ∼8 μm) oriented parallel to the cubic axis of a CaF₂ matrix. The rods present low-energy {100}_CaF2 //{111}_MgO interfaces. Light guiding was experimentally proved and considered for possible optical applications. Crack propagation was also studied to show the potential improvement in fracture toughness through crack deflection at the interfaces.