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'Fluorite' (also called 'fluorspar') is a mineral composed of calcium fluoride, CaF₂. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon. Cubic crystals up to 20cm across have been found at Dalnegorsk, Russia.^[1] Crystal twinning is common and adds complexity to the observed crystal habits.
The name fluorite is derived from the Latin ''fluo'', meaning "flow", in reference to its industrial use as a flux.

Contents

Occurrence

Blue John

Fluorescence

Uses

See also

References

External links

Gallery

Occurrence

Fluorite may occur as a vein deposit, especially with metallic minerals, where it often forms a part of the gangue (the worthless "host-rock" in which valuable minerals occur) and may be associated with galena, sphalerite, barite, quartz, and calcite. It is a common mineral in deposits of hydrothermal origin and has been noted as a primary mineral in granites and other igneous rocks and as a common minor constituent of dolostone and limestone.
Fluorite is a widely occurring mineral which is found in large deposits in many areas. Notable deposits occur in Germany, Austria, Switzerland, England, Norway, Mexico, and Ontario in Canada. Large deposits also occur in Kenya in the Kerio Valley area within the Great Rift Valley. In the United States deposits are found in Missouri, Oklahoma, Illinois, Kentucky, Colorado, New Mexico, Arizona, Ohio, New Hampshire, New York, Alaska and Texas. Illinois has historically been the largest producer of fluorite in the United States, however, the last of the mines closed in 1995.[1] The Illinois general assembly passed a resolution in 1965 declaring fluorite as the official state mineral.

Blue John

One of the most famous of the older-known localities of fluorite is Castleton in Derbyshire, England, where, under the name of 'Derbyshire Blue John', purple-blue fluorite was extracted from several mines/caves, including the famous Blue John Cavern. During the 19th century, this attractive fluorite was mined for its ornamental value. The name derives from French "''bleu et jaune''" (blue and yellow) characterising its color. Blue John is now scarce, and only a few hundred kilograms are mined each year for ornamental and lapidary use. Mining still takes place in the nearby Treak Cliff Cavern. Recent deposits in China have produced fluorite with coloring and banding similar to the classic Blue John stone.
"Blue John can only be found in one place in the world in Treak Cliff Cavern" quoted guide tours at the cavern

Fluorescence

Many samples of fluorite fluoresce under ultra-violet light, a property that takes its name from fluorite. Many minerals, as well as other substances, fluoresce. Fluorescence involves the elevation of electron energy levels by quanta of ultra-violet light, followed by the progressive falling back of the electrons into their previous energy state, releasing quanta of visible light in the process. In fluorite, the visible light emitted is most commonly blue, but red, purple, yellow, green and white also occur. The fluorescence of fluorite may be due to impurities such as yttrium or organic matter in the crystal lattice. It is not surprising, therefore, that the color of visible light emitted when a sample of fluorite is fluorescing appears dependent on where the original specimen was collected, different impurities having been included in the crystal lattice in different places. Neither do all fluorites fluoresce equally brightly, even from the same locality. Therefore ultra-violet light is not a reliable tool for the identification of specimens, nor for quantifying the mineral in mixtures. For example, among British fluorites, those from Northumberland, County Durham and Eastern Cumbria are the most consistently fluorescent, whereas fluorites from Yorkshire, Derbyshire and Cornwall, if they fluoresce at all, are generally only feebly fluorescent.
Fluorite also exhibits the property of thermoluminescence.

Uses

There are three principal types of industrial use for fluorite, corresponding to different grades of purity. Metallurgical grade fluorite, the lowest of the three grades, has traditionally been used as a flux to lower the melting point of raw materials in steel production to aid the removal of impurities, and later in the production of aluminium (aluminum). Ceramic (intermediate) grade fluorite is used in the manufacture of opalescent glass, enamels and cooking utensils. The highest grade, acid grade fluorite, is used as a feedstock in the manufacture of hydrofluoric acid, in turn used to manufacture hydrofluorocarbons and fluoropolymers.
Fluorite is used instead of glass in some high performance telescopes and camera lens elements. Exposure tools for the semiconductor industry make use of fluorite for the optics of the 157 nm wavelength, a wavelength created by an excimer laser using fluorine gas. Fluorite has a uniquely high transparency at this wavelength. Fluorite has a very low dispersion so light diffraction is far less than ordinary glass, and in telescopes it allows crisp images of astronomical objects even at high power. Fluorite is decomposed by sulfuric acid to form free hydrofluoric acid, which etches glass. Fluorite also has ornamental and lapidary uses.

See also

★ List of minerals

References

★ Hurlbut, Cornelius S.; Klein, Cornelis, 1985, ''Manual of Mineralogy'', pp. 324 - 325, 20th ed., ISBN 0-471-80580-7

★ Mineral Galleries

★ Webmineral

★ Mindat.org

★ Fluorspar
1. ''The Complete Encyclopedia of Minerals'' by P. Korbel and M. Novak

External links

★ an educational tour of Weardale Fluorite

★ Illinois State Geologic Survey

★ Illinois state mineral

★ Barber Cup and Crawford Cup, related Roman cups at British Museum.

★ Fluorites and antifluorites at NCSU

★ Spanish Fluorite

Gallery