Calcium fluoride (CaF₂) occurs naturally as the mineral fluorite or fluorspar. It is the world′s main source of fluorine. It is used in the optical industry because of its transparency in both infrared (IR) and ultraviolet (UV) wavelengths (about 0.15 to 9 μm). Due to its low refractive index (n500 = 1.44), it is considered a promising candidate for antireflective coatings. Chemically, CaF₂ is relatively stable; optical components will not be harmed under adverse conditions.