Calcium fluoride (CaF2) is the major source of fluorine worldwide. It occurs as the mineral fluorite or fluorite. Unlike other calcium halides, it is practically insoluble in water.
Calcium fluoride is used in the manufacture of optical components such as windows and lenses for thermal imaging systems, spectroscopy, telescopes and excimer lasers (in the form of fused lenses for lithography). It is transparent over a broad range of frequencies from ultraviolet (UV) to infrared (IR). Its low refractive index reduces the need for anti-reflective coatings. Its insolubility in water is also handy. [citation needed] It also allows smaller wavelengths to pass. [citation needed]
Doped calcium fluoride, like natural fluorite, exhibits thermoluminescence and is used in thermoluminescent dosimeters. Formed when fluorine combines with calcium.
Naturally occurring CaF2 is a major source of hydrogen fluoride,[clarification needed] a commodity chemical used in the production of various materials. Calcium fluoride in the fluorite state is of commercial importance as a fluoride source. [11] Hydrogen fluoride is liberated from minerals by the action of concentrated sulfuric acid:[12]
CaF2 + H2SO4 → CaSO4 (solid) + 2 HF
Ca2+ centers are octacoordinates, centered on a cube of eight F- centers. Each F- center coordinates with four Ca2+ centers of tetrahedral shape. [5] Although perfectly packed crystal samples are colorless, minerals are often dark in color due to the presence of F centers. The same crystal structure is found in many ionic compounds of formula AB2, such as CeO2, cubic ZrO2, UO2, ThO2, and PuO2. In the corresponding inverse structure, called the inverse fluorite structure, the anions and cations are exchanged, such as Be2C.
