(also fluorspar), a mineral of the fluoride group, with the chemical composition CaF₂. Small amounts of Ca are sometimes replaced by Y (yielding yttrofluorite), rare-earth elements, Sr, Mn, Na, or U. Fluorite crystallizes in the isometric system, forming the fluorite structure (seeCRYSTAL STRUCTURE). Most fluorite crystals are cubes or octahedrons. The massive varieties may be composite, coarsely crystalline, granular, or earthy; one of the earthy varieties is ratovkite.

Fluorite has a hardness of 4 on Mohs’ scale, a density of 3,180–3,200 kg/m³, and a melting point of 1360°C. The density of yttrofluorite can be as high as 3,300 kg/m³. The mineral comes in various colors, for example, yellow, green, or violet. The coloration is often banded or patchy owing to the formation of color centers. Fluorite is characterized by luminescence upon exposure to ultraviolet radiation. The luminescence is caused by impurity centers: Eu²⁺ ions in the blue-violet region of the spectrum and Yb²⁺ ions in the yellow-green region. Thermoluminescence due to Mn²⁺ ions and triply ionized atoms of rare-earth elements is observed. Fluorite is isotropic, has a low dispersion and a low refractive index (1.434), and is transparent in the wavelength range 0.0125–10 micrometers. The transparency to such radiation makes fluorite a valuable optical raw material.

Fluorite is a common mineral and occurs in many different kinds of deposits. It is deposited overa broad temperature range, is primarily hydrothermal and metasomatic, and is sometimes found as ratovkite in sedimentary rocks. It is an important typomorphic mineral in genetic mineralogy.

Fluorite is used in metallurgy as a flux, in the chemical industry to produce hydrofluoric acid and cryolite, and in ceramics to manufacture enamels and glazes. It is also employed as the stock material for growing synthetic fluorite crystals. Pure transparent colorless or slightly tinted varieties of fluorite are used in optics to manufacture lenses, objectives, telescopes, and prisms for vacuum and X-ray spectrographs. Synthetic fluorite doped with rare-earth elements or uranium is a laser material.

The fluorite deposits in the USSR include those at Voznesenskoe in the Primor’e Krai, Solonechnoe in Middle Asia, Abagaituiskoe in Transbaikalia, and Taskainar in Kazakhstan. Outside the USSR, fluorite deposits are found in the USA, Mexico, France, and other countries. The deposits in the USA include those at Cave in Rock, 111., and in the Rocky Mountains.