Low grade MgF2 is sometimes used in the infrared but it is inferior to CaF2. MgF2 is tough and works and polishes well, but it is slightly birefringent and should be cut with the optic axis perpendicular to the plane of the window or lens.
Highly recommended MgF2 Optics from Yutai Optics:
MgF2 lenses,
MgF2 windows,
MgF2 domes,
MgF2 prisms.
MgF2 Transmittance 2-14μm&200-1100nm Chart: