Editing Fluorite

{{short description|Mineral form of calcium fluoride}}
{{distinguish|Fluoride}}
{{Infobox mineral
| name       =  Fluorite
| category    = [[Halide mineral]]
| boxwidth    =
| boxbgcolor  =#305c3c
| boxtextcolor = #fff
| image       = 3192M-fluorite1.jpg
| imagesize   = 260px
| caption     = Deep green isolated fluorite crystal resembling a [[truncated octahedron]], set upon a micaceous matrix, from Erongo Mountain, Erongo Region, [[Namibia]] (overall size: 50 mm × 27 mm, crystal size: 19 mm wide, 30 g)
| formula     = CaF<sub>2</sub>
| IMAsymbol   = Flr<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>
| molweight   =
| strunz      = 3.AB.25
| system      = [[Cubic crystal system|Isometric]]
| class       = Hexoctahedral (m{{overline|3}}m) <br />[[H–M symbol]]: (4/m {{overline|3}} 2/m) <br />([[Pearson symbol|cF12]])
| symmetry    = ''F''m{{overline|3}}m (No. 225)
| unit cell   = a = 5.4626&nbsp;Å; Z&nbsp;=&nbsp;4
| color       = Colorless, although samples are often deeply colored owing to impurities; Purple, lilac, golden-yellow, green, blue, pink, champagne, brown.
| habit       = Well-formed coarse sized crystals; also nodular, botryoidal, rarely columnar or fibrous; granular, massive
| twinning    = Common on {111}, interpenetrant, flattened
| cleavage    = Octahedral, perfect on {111}, parting on {011}
| fracture    = Subconchoidal to uneven
| tenacity    = Brittle
| mohs        = 4 (defining mineral)
| luster      = Vitreous
| refractive  = 1.433–1.448
| opticalprop = Isotropic; weak anomalous anisotropism; moderate [[Optical relief|relief]]
| birefringence =
| pleochroism =
| streak      = White
| gravity     = 3.175–3.184; to 3.56 if high in rare-earth elements
| melt        =
| fusibility  = 3
| diagnostic  =
| solubility  = slightly water soluble and in hot [[hydrochloric acid]]
| diaphaneity = Transparent to translucent
| other       = May be [[fluorescence|fluorescent]], [[phosphorescence|phosphorescent]], [[thermoluminescence|thermoluminescent]], and/or [[triboluminescence|triboluminescent]]
| references=<ref name=Handbook>{{cite book|editor1=Anthony, John W. |editor2=Bideaux, Richard A. |editor3=Bladh, Kenneth W. |editor4=Nichols, Monte C. |title= Handbook of Mineralogy|publisher= Mineralogical Society of America|place= Chantilly, VA, US|url=http://rruff.geo.arizona.edu/doclib/hom/fluorite.pdf |archive-url=https://web.archive.org/web/20060906161859/http://rruff.geo.arizona.edu/doclib/hom/fluorite.pdf |archive-date=2006-09-06 |url-status=live|chapter=Fluorite |date=1990 |access-date=December 5, 2011|isbn=0962209724 |volume=III (Halides, Hydroxides, Oxides)}}</ref><ref name=Mindat/><ref name=Webmin>[http://webmineral.com/data/Fluorite.shtml Fluorite]. Webmineral.com</ref><ref name=Hurlbut>Hurlbut, Cornelius S.; Klein, Cornelis, 1985, ''Manual of Mineralogy'', pp. 324–325, 20th ed., {{ISBN|0-471-80580-7}}</ref>
}}

'''Fluorite''' (also called '''fluorspar''') is the mineral form of [[calcium fluoride]], CaF<sub>2</sub>. It belongs to the [[halide mineral]]s. It crystallizes in [[cubic crystal system|isometric]] [[crystal habit|cubic habit]], although octahedral and more complex isometric forms are not uncommon.

The [[Mohs scale of mineral hardness]], based on [[Scratch hardness|scratch]] [[hardness comparison]], defines value 4 as fluorite.<ref>{{cite journal |title=Mohs's Hardness Scale - A Physical Interpretation
|first1=D. |last1=Tabor |year=1954 |journal=Proc. Phys. Soc. B |volume=67 |issue=3 |page=249 |doi=10.1088/0370-1301/67/3/310 |bibcode=1954PPSB...67..249T |url=https://iopscience.iop.org/article/10.1088/0370-1301/67/3/310/pdf |access-date=19 January 2022}}</ref>

Pure fluorite is colourless and transparent, both in visible and ultraviolet light, but impurities usually make it a colorful mineral and the stone has ornamental and [[lapidary]] uses. Industrially, fluorite is used as a [[flux (metallurgy)|flux]] for smelting, and in the production of certain glasses and enamels. The purest grades of fluorite are a source of fluoride for [[hydrofluoric acid]] manufacture, which is the intermediate source of most fluorine-containing [[fine chemical]]s. Optically clear transparent fluorite has anomalous partial [[dispersion (optics)|dispersion]], that is, its refractive index varies with the wavelength of light in a manner that differs from that of commonly used glasses, so fluorite is useful in making [[apochromat|apochromatic lenses]], and particularly valuable in photographic optics. Fluorite optics are also usable in the far-ultraviolet and mid-infrared ranges, where conventional glasses are too opaque for use. Fluorite also has low dispersion, and a high refractive index for its density.

==History and etymology==

The word ''fluorite'' is derived from the [[Latin]] verb ''fluere'', meaning ''to flow''. The mineral is used as a [[flux (metallurgy)|flux]] in iron [[smelting]] to decrease the [[viscosity]] of [[slag]]. The term ''flux'' comes from the Latin adjective ''fluxus'', meaning ''flowing, loose, slack''. The mineral fluorite was originally termed '''fluorspar''' and was first discussed in print in a 1530 work ''Bermannvs sive de re metallica dialogus'' [Bermannus; or dialogue about the nature of metals], by [[Georgius Agricola]], as a mineral noted for its usefulness as a flux.<ref name="awe">{{cite web|title=Discovery of fluorine|publisher=Fluoride History |url=http://www.fluoride-history.de/fluorine.htm}}</ref><ref name="assassinated">{{cite book|url=https://books.google.com/books?id=Fl4sdCYrq3cC&pg=PT158|isbn=978-0-444-52239-9|page=149|author=compiled by Alexander Senning.|year=2007|publisher=Elsevier|location=Amsterdam|title=Elsevier's dictionary of chemoetymology: the whies and whences of chemical nomenclature and terminology}}</ref> Agricola, a German scientist with expertise in [[philology]], [[mining]], and metallurgy, named fluorspar as a [[Neo-Latin]]ization of the [[German language|German]] ''Flussspat'' from ''Fluss'' ([[stream]], [[river]]) and ''Spat'' (meaning a [[Nonmetal (chemistry)|nonmetal]]lic mineral akin to [[gypsum]], spærstān, ''[[spar (mineralogy)|spear stone]]'', referring to its crystalline projections).<ref>{{OEtymD|fluorite}}</ref><ref>{{OEtymD|spar}}</ref>

In 1852, fluorite gave its name to the phenomenon of [[fluorescence]], which is prominent in fluorites from certain locations, due to certain impurities in the crystal. Fluorite also gave the name to its constitutive element [[fluorine]].<ref name=Mindat>[http://www.mindat.org/min-1576.html Fluorite]. Mindat.org</ref> Currently, the word "fluorspar" is most commonly used for fluorite as an industrial and chemical commodity, while "fluorite" is used mineralogically and in most other senses.

In archeology, gemmology, classical studies, and Egyptology, the Latin terms ''murrina'' and ''myrrhina'' refer to fluorite.<ref>James Harrell 2012. UCLA Encyclopedia of Egyptology, Gemstones.</ref> In book 37 of his ''[[Naturalis Historia]]'', [[Pliny the Elder]] describes it as a precious stone with purple and white mottling, and noted that the Romans prized objects carved from it.  It has been suggested that the Sanskrit mineral name ''vaikrānta'' (वैक्रान्तः), known from [[Rasashastra|Sanskrit alchemical texts]] dating from the early second millennium CE onwards, may refer to fluorite.<ref>{{Cite journal |last=Murthy |first=S. R. N. |date=1983-12-01 |title=Minerals Used in Indian Medicine |url=https://pubs.geoscienceworld.org/jour-geosocindia/article/24/12/664/640580/Minerals-Used-in-Indian-Medicine |journal=Journal of the Geological Society of India |language=en |volume=24 |issue=12 |page=666 |doi=10.17491/jgsi/1983/241206 |bibcode=1983JGSI...24..664M |issn=0974-6889}}</ref>

==Structure==
{{Main|Calcium fluoride}}
[[File:Fluorite Structure.jpg|thumb|left|upright|The structure of calcium fluoride CaF<sub>2</sub>.<ref>{{Greenwood&Earnshaw2nd}}</ref>]]

Fluorite [[crystallization|crystallizes]] in a [[cubic crystal system|cubic motif]]. [[Crystal twinning]] is common and adds complexity to the observed [[crystal habit]]s. Fluorite has four perfect cleavage planes that help produce [[octahedron|octahedral]] fragments.<ref name="nesse">{{cite book |last=Nesse|first=William D. |title=Introduction to mineralogy |date=2000 |publisher=[[Oxford University Press]] |location=New York |isbn=9780195106916 |pages=376–77}}</ref> The structural motif adopted by fluorite is so common that the motif is called the [[fluorite structure]]. Element substitution for the [[calcium]] [[cation]] often includes [[strontium]] and certain [[rare-earth element]]s (REE), such as [[yttrium]] and [[cerium]].<ref name=Hurlbut/>

==Occurrence and mining==
[[File:Closeup of Fluorite.jpg|thumb|A closeup of fluorite surface|alt=black, chevronned (wavy, jagged) structure]]
Fluorite forms as a late-crystallizing mineral in [[felsic]] [[igneous]] rocks typically through hydrothermal activity.<ref name="Deer 2013 p. ">{{cite book | last=Deer | first=W. A. | title=An introduction to the rock-forming minerals | publisher=The Mineralogical Society | location=London | year=2013 | isbn=978-0-903056-27-4 | oclc=858884283 }}</ref> It is particularly common in granitic pegmatites. It may occur as a [[Vein (geology)|vein deposit]] formed through [[hydrothermal]] activity particularly in limestones. In such vein deposits it can be associated with [[galena]], [[sphalerite]], [[barite]], [[quartz]], and [[calcite]]. Fluorite can also be found as a constituent of sedimentary rocks either as grains or as the cementing material in [[sandstone]].<ref name="Deer 2013 p. "/>

It is a common mineral mainly distributed in South Africa, China, Mexico, Mongolia, the United Kingdom, the United States, Canada, Tanzania, Rwanda and Argentina.

The world reserves of fluorite are estimated at 230 million [[tonne]]s (Mt) with the largest deposits being in [[South Africa]] (about 41 Mt), Mexico (32 Mt) and China (24 Mt). China is leading the world production with about 3 Mt annually (in 2010), followed by Mexico (1.0 Mt), [[Mongolia]] (0.45 Mt), [[Russia]] (0.22 Mt), South Africa (0.13 Mt), Spain (0.12 Mt) and Namibia (0.11 Mt).<ref>[http://minerals.usgs.gov/minerals/pubs/commodity/fluorspar/mcs-2011-fluor.pdf Fluorspar]. USGS.gov (2011)</ref>{{Update inline|reason=Says, in 2010, China had 24 Mt and was mining 3 Mt annually, so now should have none|date=December 2019}}

One of the largest deposits of fluorspar in North America is located on the [[Burin Peninsula]], [[Newfoundland (island)|Newfoundland]], Canada. The first official recognition of fluorspar in the area was recorded by geologist J.B. Jukes in 1843. He noted an occurrence of "galena" or lead ore and fluoride of lime on the west side of St. Lawrence harbour. It is recorded that interest in the commercial mining of fluorspar began in 1928 with the first ore being extracted in 1933. Eventually, at Iron Springs Mine, the shafts reached depths of {{convert|970|ft|m}}. In the St. Lawrence area, the veins are persistent for great lengths and several of them have wide [[Lens (geology)|lenses]]. The area with veins of known workable size comprises about {{convert|60|sqmi|km2}}.<ref>[https://web.archive.org/web/20110708113037/http://www.canadafluorspar.com/BML_Proj_Registration_Master.pdf Reactivation of the St. Lawrence fluorspar mine at St. Lawrence, NL]. Burin Minerals Ltd. (April 9, 2009).</ref><ref>{{cite journal|last1=Van Alstine|first1=R. E.|title=The fluorspar deposits of Saint Lawrence, Newfoundland|journal=Economic Geology|volume=39|page=109|year=1944|doi=10.2113/gsecongeo.39.2.109|issue=2|bibcode=1944EcGeo..39..109V }}</ref><ref>{{cite journal|last1=Strong|first1=D. F.|last2=Fryer|first2=B. J.|last3=Kerrich|first3=R.|title=Genesis of the St. Lawrence fluorspar deposits as indicated by fluid inclusion, rare earth element, and isotopic data|journal=Economic Geology|volume=79|page=1142|year=1984|doi=10.2113/gsecongeo.79.5.1142|issue=5|bibcode=1984EcGeo..79.1142S }}</ref> 

In 2018, Canada Fluorspar Inc. commenced mine production again<ref>{{cite web|url=https://www.cbc.ca/news/canada/newfoundland-labrador/fluorspar-mine-investment-st-lawrence-1.4026074|title=St. Lawrence fluorspar mine gets $5M from feds, hundreds of jobs touted|website=Cbc.ca|access-date=14 December 2021}}</ref> in St. Lawrence; in spring 2019, the company was planned to develop a new shipping port on the west side of Burin Peninsula as a more affordable means of moving their product to markets,<ref>{{Cite web|url=https://www.saltwire.com/newfoundland-labrador/news/local/cfi-seeking-new-location-for-shipping-port-in-st-lawrence-nl-305947/|title=CFI seeking new location for shipping port in St. Lawrence, NL &#124; SaltWire|first=Colin|last=Farrell|website=Saltwire.com|access-date=14 December 2021}}</ref> and they successfully sent the first shipload of ore from the new port on July 31, 2021. This marks the first time in 30 years that ore has been shipped directly out of St. Lawrence.<ref>{{Cite web|url=https://vocm.com/2021/07/31/first-shipment-of-fluorspar-in-over-30-years-exported-from-st-lawrence/|title=First Shipment of Fluorspar in Over 30 Years Exported From St. Lawrence|first=Noah|last=Sheppard|website=Vocm.com|access-date=14 December 2021}}</ref>

Cubic crystals up to 20&nbsp;cm across have been found at [[Dalnegorsk]], Russia.<ref>Korbel, P. and Novak, M. (2002) ''The Complete Encyclopedia of Minerals'', Book Sales, {{ISBN|0785815201}}.</ref> The largest documented single crystal of fluorite was a cube 2.12 meters in size and weighing approximately 16 tonnes.<ref>{{cite journal |url=http://www.minsocam.org/ammin/AM66/AM66_885.pdf |archive-url=https://web.archive.org/web/20090620081033/http://www.minsocam.org/ammin/AM66/AM66_885.pdf |archive-date=2009-06-20 |url-status=live|journal=American Mineralogist|volume=66|pages=885–907|year=1981|title=The largest crystals|author=Rickwood, P. C.}}</ref>  
[[File:Barite-Fluorite-fluoritespain.jpg|thumb|Fluorite on barite from the Berbes mine, Ribadesella, Asturias (Spain).  Fluorite crystal, 2.2 cm. ]]
In [[Asturias]] ([[Spain]]) there are several fluorite deposits known internationally for the quality of the specimens they have yielded. In the area of [[Berbes]], [[Ribadesella]], fluorite appears as cubic crystals, sometimes with dodecahedron modifications, which can reach a size of up to 10 cm of edge, with internal colour zoning, almost always violet in colour. It is associated with quartz and leafy aggregates of baryte. In the ''Emilio'' mine, in Loroñe, [[Colunga]], the fluorite crystals, cubes with small modifications of other figures, are colourless and transparent. They can reach 10 cm of edge. In the ''Moscona'' mine, in Villabona, the fluorite crystals, cubic without modifications of other shapes, are yellow, up to 3 cm of edge. They are associated with large crystals of calcite and barite.<ref>{{Cite book |last1=Calvo Sevillano |first1=Guiomar |title=Fluorite. The Collector's Choice |last2=Calvo Rebollar |first2=Miguel |publisher=Lithographie LLC. Connecticut, USA |year=2006 |location=Connecticut, USA |pages=38–42 |chapter=Fluorite from Spain. Every color under the Sun}}</ref>

==="Blue John"===<!-- This section is linked from [[Peak District]] -->
{{Main|Blue John (mineral)}}
One of the most famous of the older-known localities of fluorite is [[Castleton, Derbyshire|Castleton]] in [[Derbyshire]], [[England]], where, under the name of "Derbyshire Blue John", purple-blue fluorite was extracted from several mines or caves. During the 19th century, this attractive fluorite was mined for its ornamental value. The mineral 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 [[Blue John Cavern]] and [[Treak Cliff Cavern]].<ref>{{cite book|title=Chemistry in context|author1=Hill, Graham  |author2=Holman, John |year=2000|isbn=0174482760|publisher=Nelson Thornes}}</ref>

Recently discovered deposits in China have produced fluorite with coloring and banding similar to the classic Blue John stone.<ref>{{cite journal|last1=Ford|first1=Trevor D.|title=Blue John fluorspar|journal=Geology Today|volume=10|page=186|year=1994|doi=10.1111/j.1365-2451.1994.tb00422.x|issue=5|bibcode=1994GeolT..10..186F }}</ref>

==Fluorescence==
[[File:FluoriteUV.jpg|thumb|left|Fluorescing fluorite from Boltsburn Mine, [[Weardale]], [[North Pennines]], [[County Durham]], England, UK.]]
[[George Gabriel Stokes]] named the phenomenon of ''fluorescence'' from fluorite, in 1852.<ref name=stokes1>{{cite journal|title=On the Change of Refrangibility of Light|author=Stokes, G. G.|year=1852|journal=[[Philosophical Transactions of the Royal Society of London]]|volume=142|pages=463–562|doi=10.1098/rstl.1852.0022|doi-access=free}}</ref><ref>{{cite journal|title=On the Change of Refrangibility of Light. No. II|author=Stokes, G. G.|jstor=108570|year=1853|journal=Philosophical Transactions of the Royal Society of London|volume=143|pages=385–396, at p.&nbsp;387|doi=10.1098/rstl.1853.0016|s2cid=186207789}}</ref>

Many samples of fluorite exhibit [[fluorescence]] under [[ultraviolet light]], a property that takes its name from fluorite.<ref name=stokes1/> Many minerals, as well as other substances, fluoresce. Fluorescence involves the elevation of electron energy levels by quanta of ultraviolet 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 mineral impurities, such as [[yttrium]] and [[ytterbium]], or organic matter, such as volatile [[hydrocarbons]] in the crystal lattice. In particular, the blue fluorescence seen in fluorites from certain parts of [[Great Britain]] responsible for the naming of the phenomenon of fluorescence itself, has been attributed to the presence of inclusions of divalent [[europium]] in the crystal.<ref>{{cite journal|last1=Przibram|first1=K.|title=Fluorescence of Fluorite and the Bivalent Europium Ion|journal=Nature|volume=135|page=100|year=1935|doi=10.1038/135100a0|issue=3403|bibcode=1935Natur.135..100P|s2cid=4104586|doi-access=free}}</ref> Natural samples containing rare earth impurities such as [[erbium]] have also been observed to display [[Photon upconversion|upconversion fluorescence]], in which infrared light stimulates emission of visible light, a phenomenon usually only reported in synthetic materials.<ref>{{Cite journal|last1=Moffatt|first1=Jillian Elizabeth|last2=Payten|first2=Thomas Bede|last3=Tsiminis|first3=Georgios|last4=Prinse|first4=Thomas Jacob de|last5=Teixeira|first5=Lewis Da Silva|last6=Klantsataya|first6=Elizaveta|last7=Ottaway|first7=David John|last8=Smith|first8=Barnaby Whitmore|last9=Spooner|first9=Nigel Antony|date=2021-01-07|title=Upconversion Fluorescence in Naturally Occurring Calcium Fluoride|url=https://journals.sagepub.com/doi/10.1177/0003702820979052|journal=Applied Spectroscopy|volume=75|issue=6|pages=674–689|language=en|doi=10.1177/0003702820979052|pmid=33241707|bibcode=2021ApSpe..75..674M|s2cid=227176307}}</ref>

One fluorescent variety of fluorite is [[chlorophane]], which is reddish or purple in color and fluoresces brightly in emerald green when heated ([[thermoluminescence]]), or when illuminated with ultraviolet light.

The color of visible light emitted when a sample of fluorite is fluorescing depends on where the original specimen was collected; different impurities having been included in the crystal lattice in different places. Neither does all fluorite fluoresce equally brightly, even from the same locality. Therefore, ultraviolet 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 fluorite from [[Yorkshire]], [[Derbyshire]], and [[Cornwall]], if they fluoresce at all, are generally only feebly fluorescent.

Fluorite also exhibits the property of [[thermoluminescence]].<ref>{{cite book|url=https://books.google.com/books?id=6pNoV48kNSsC&pg=PA9|page=9|title=Thermoluminescence of Solids|author=McKeever, S. W. S. |publisher=Cambridge University Press|year=1988|isbn=0-521-36811-1}}</ref>
{{Clear}}

==Color==
Fluorite is allochromatic, meaning that it can be tinted with elemental impurities. Fluorite comes in a wide range of colors and has consequently been dubbed "the most colorful mineral in the world". Every color of the rainbow in various shades is represented by fluorite samples, along with white, black, and clear crystals. The most common colors are purple, blue, green, yellow, or colorless. Less common are pink, red, white, brown, and black. Color zoning or banding is commonly present. The color of the fluorite is determined by factors including impurities, exposure to radiation, and the absence of voids of the [[F-center|color centers]].

<gallery widths="133px" heights="130px">

File:Fluorite-Galena-flu70a.jpg|Pastel green fluorite crystal on galena
File:Fluorite-132158.jpg|A golden yellow with hints of purple fluorite
File:Fluorite-cflo06x.jpg|Freestanding purple fluorite cluster between two quartzes
File:Fluorite-189396.jpg|Light to dark burgundy color fluorite
File:Fluorite-158842.jpg|Transparent teal color fluorite with purple highlights
File:Fluorite-233168.jpg|Grass-green fluorite octahedrons clustered on a quartz-rich matrix
</gallery>

==Uses==

===Source of fluorine and fluoride===
Fluorite is a major source of [[hydrogen fluoride]], a commodity chemical used to produce a wide range of materials. Hydrogen fluoride is liberated from the mineral by the action of concentrated [[sulfuric acid]]:
:CaF<sub>2</sub>([[solid|s]]) + H<sub>2</sub>SO<sub>4</sub> → [[calcium sulfate|CaSO<sub>4</sub>]](s) + 2 HF([[gas|g]])

The resulting HF is converted into fluorine, [[fluorocarbon]]s, and diverse fluoride materials. As of the late 1990s, five billion kilograms were mined annually.<ref name=Aigueperse>{{Cite book |first= Jean |last= Aigueperse |author2=Paul Mollard |author3=Didier Devilliers |author4=Marius Chemla |author5=Robert Faron |author6=Renée Romano |author7=Jean Pierre Cuer |contribution= Fluorine Compounds, Inorganic |title= Ullmann's Encyclopedia of Industrial Chemistry |year= 2005 |publisher= Wiley-VCH |place= Weinheim|doi= 10.1002/14356007.a11_307 |isbn= 3527306730}}</ref>

There are three principal types of industrial use for natural fluorite, commonly referred to as "fluorspar" in these industries, corresponding to different grades of purity. Metallurgical grade fluorite (60–85% CaF<sub>2</sub>), the lowest of the three grades, has traditionally been used as a [[flux (metallurgy)|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]]. Ceramic grade fluorite (85–95% CaF<sub>2</sub>) is used in the manufacture of [[opalescence|opalescent]] [[glass]], [[vitreous enamel|enamels]], and cooking utensils. The highest grade, "acid grade fluorite" (97% or more CaF<sub>2</sub>), accounts for about 95% of fluorite consumption in the US where it is used to make [[hydrogen fluoride]] and [[hydrofluoric acid]] by reacting the fluorite with [[sulfuric acid]].<ref name=usgs/>

Internationally, acid-grade fluorite is also used in the production of [[Aluminium fluoride|AlF<sub>3</sub>]] and [[cryolite]] (Na<sub>3</sub>AlF<sub>6</sub>), which are the main fluorine compounds used in aluminium smelting. [[Alumina]] is dissolved in a bath that consists primarily of molten Na<sub>3</sub>AlF<sub>6</sub>, AlF<sub>3</sub>, and fluorite (CaF<sub>2</sub>) to allow electrolytic recovery of aluminium. Fluorine losses are replaced entirely by the addition of AlF<sub>3</sub>, the majority of which react with excess sodium from the alumina to form Na<sub>3</sub>AlF<sub>6</sub>.<ref name=usgs>Miller, M. Michael. [http://minerals.usgs.gov/minerals/pubs/commodity/fluorspar/myb1-2009-fluor.pdf Fluorspar], USGS 2009 Minerals Yearbook</ref>

===Niche uses===
[[File:Fluorite Crawford Cup AD 50 100.jpg|thumb|Crawford Cup (Roman, 50-100 CE) in the collection of the [[British Museum]].<ref>{{cite web|title=The Crawford Cup|url=https://www.britishmuseum.org/explore/highlights/highlight_objects/gr/t/the_crawford_cup.aspx|publisher=[[British Museum]]|access-date=20 December 2014}}</ref> Made of fluorite.]]

====Lapidary uses====
Natural fluorite mineral has ornamental and [[lapidary]] uses. Fluorite may be drilled into beads and used in jewelry, although due to its relative softness it is not widely used as a semiprecious stone. It is also used for ornamental carvings, with expert carvings taking advantage of the stone's zonation.

====Optics====
{{See also|Fluoride glass}}
In the laboratory, calcium fluoride is commonly used as a window material for both [[infrared]] and [[ultraviolet]] wavelengths, since it is transparent in these regions (about 150 to 9000&nbsp;nm) and exhibits an extremely low change in [[refractive index]] with wavelength. Furthermore, the material is attacked by few reagents. At wavelengths as short as 157&nbsp;nm, a common wavelength used for [[semiconductor]] stepper manufacture for [[integrated circuit]] [[Photolithography|lithography]], the refractive index of calcium fluoride shows some non-linearity at high power densities, which has inhibited its use for this purpose. In the early years of the 21st century, the stepper market for calcium fluoride collapsed, and many large manufacturing facilities have been closed. [[Canon Inc.|Canon]] and other manufacturers have used synthetically grown crystals of calcium fluoride components in lenses to aid [[apochromatic]] design, and to reduce [[Dispersion (optics)|light dispersion]]. This use has largely been superseded by newer glasses and computer-aided design. As an infrared optical material, calcium fluoride is widely available and was sometimes known by the [[Eastman Kodak]] trademarked name "Irtran-3", although this designation is obsolete.

Fluorite should not be confused with fluoro-crown (or fluorine crown) glass, a type of [[low-dispersion glass]] that has special optical properties approaching fluorite. True fluorite is not a glass but a crystalline material. Lenses or [[List of lens designs|optical groups]] made using this low dispersion glass as one or more elements exhibit less [[chromatic aberration]] than those utilizing conventional, less expensive [[Crown glass (optics)|crown glass]] and [[flint glass]] elements to make an [[achromatic lens]]. Optical groups employ a combination of different types of glass; each type of glass [[Refraction|refracts]] light in a different way. By using combinations of different types of glass, lens manufacturers are able to cancel out or significantly reduce unwanted characteristics; chromatic aberration being the most important. The best of such lens designs are often called apochromatic (see above). Fluoro-crown glass (such as Schott FK51) usually in combination with an appropriate [[Flint glass|"flint" glass]] (such as Schott KzFSN 2) can give very high performance in telescope objective lenses, as well as microscope objectives, and camera telephoto lenses. Fluorite elements are similarly paired with complementary "flint" elements (such as Schott LaK 10).<ref>{{cite web|url=https://www.schott.com/advanced_optics/english/knowledge-center/technical-articles-and-tools/abbe-diagramm.html|title=Interactive Abbe Diagram|publisher=SCHOTT AG|year=2019|access-date=February 20, 2018}}</ref> The refractive qualities of fluorite and of certain flint elements provide a lower and more uniform dispersion across the spectrum of visible light, thereby keeping colors focused more closely together. Lenses made with fluorite are superior to fluoro-crown based lenses, at least for doublet telescope objectives; but are more difficult to produce and more costly.<ref>Rutten, Harrie; van Venrooij, Martin (1988). Telescope Optics Evaluation and Design.  Willmann-Bell, Inc.</ref>

The use of fluorite for prisms and lenses was studied and promoted by [[Victor Schumann]] near the end of the 19th century.<ref name="Lyman">{{Cite journal|last=Lyman|first=T.|title=Victor Schumann|journal=Astrophysical Journal|volume=38|pages=1–4|year=1914|doi=10.1086/142050|bibcode=1914ApJ....39....1L|doi-access=free}}</ref> Naturally occurring fluorite crystals without optical defects were only large enough to produce microscope objectives.

With the advent of synthetically grown fluorite crystals in the 1950s - 60s, it could be used instead of glass in some high-performance [[optical telescope]] and [[camera lens]] elements. In telescopes, fluorite elements allow high-resolution images of astronomical objects at high [[magnification]]s. [[Canon Inc.]] produces synthetic fluorite crystals that are used in their better [[telephoto lens]]es. The use of fluorite for telescope lenses has declined since the 1990s, as newer designs using fluoro-crown glass, including triplets, have offered comparable performance at lower prices. Fluorite and various combinations of fluoride compounds can be made into synthetic crystals which have applications in lasers and special optics for UV and infrared.<ref>{{cite book|url=https://books.google.com/books?id=ZqTkCF6Ra9kC&pg=PA339|page=339|title=Bulk crystal growth of electronic, optical & optoelectronic materials|author=Capper, Peter |publisher=John Wiley and Sons|year= 2005|isbn=0-470-85142-2}}</ref>

Exposure tools for the [[semiconductor]] industry make use of fluorite optical elements for [[ultraviolet light]] at [[wavelength]]s of about 157 [[nanometer]]s. Fluorite has a uniquely high transparency at this wavelength. Fluorite [[Objective (optics)|objective lenses]] are manufactured by the larger microscope firms (Nikon, [[Olympus Corporation|Olympus]], [[Carl Zeiss AG|Carl Zeiss]] and Leica). Their transparence to ultraviolet light enables them to be used for [[Fluorescence microscope|fluorescence microscopy]].<ref>{{cite book|url=https://books.google.com/books?id=IaQOh28E0vgC&pg=PA157|page=157|title=Photography with a microscope|author1=Rost, F. W. D.  |author2=Oldfield, Ronald Jowett |publisher=Cambridge University Press|year=2000|isbn=0-521-77096-3}}</ref> The fluorite also serves to correct [[optical aberration]]s in these lenses. [[Nikon]] has previously manufactured at least one fluorite and synthetic quartz element camera lens (105&nbsp;mm f/4.5 UV) for the production of [[ultraviolet photography|ultraviolet images]].<ref>{{cite book|url=https://books.google.com/books?id=AEFPNfghI3QC&pg=PA388|pages=387–388|title=Scientific photography and applied imaging|author=Ray, Sidney F. |publisher=Focal Press|year=1999|isbn=0-240-51323-1}}</ref> [[Konica]] produced a fluorite lens for their SLR cameras – the Hexanon 300&nbsp;mm f/6.3.

==Source of fluorine gas in nature==
In 2012, the first source of naturally occurring fluorine gas was found in fluorite mines in Bavaria, Germany. It was previously thought that [[fluorine gas]] did not occur naturally because it is so reactive, and would rapidly react with other chemicals.<ref>[http://www.labspaces.net/121513/First_direct_evidence_that_elemental_fluorine_occurs_in_nature First direct evidence that elemental fluorine occurs in nature]. Labspaces.net (2012-07-06). Retrieved on 2013-08-05.</ref> Fluorite is normally colorless, but some varied forms found nearby look black, and are known as 'fetid fluorite' or [[antozonite]]. The minerals, containing small amounts of [[uranium]] and its daughter products, release radiation sufficiently energetic to induce oxidation of fluoride anions within the structure, to fluorine that becomes trapped inside the mineral. The color of fetid fluorite is predominantly due to the [[calcium]] atoms remaining. Solid-state fluorine-19 [[Nuclear magnetic resonance|NMR]] carried out on the gas contained in the antozonite, revealed a peak at 425&nbsp;ppm, which is consistent with F<sub>2</sub>.<ref>Withers, Neil (1 July 2012) [http://www.rsc.org/chemistryworld/2012/07/fluorine-finally-found-nature Fluorine finally found in nature |Chemistry World]. Rsc.org.</ref>

==Gallery==
<gallery widths="133px" heights="130px">

File:Fluorite crystals (Cullen Hall of Gems and Minerals).jpg|Fluorite crystals on display at the Cullen Hall of Gems and Minerals, [[Houston Museum of Natural Science]]
File:Fluorite and sphalerite J1.jpg|Fluorite and sphalerite, from Elmwood mine, Smith county, Tennessee, US
File:Fluorite-Quartz-226312.jpg|Translucent ball of botryoidal fluorite perched on a calcite crystal
File:FluoriteBerbes.jpg|Fluorite with baryte, from Berbes Mine, Berbes Mining area, Ribadesella, Asturias, Spain
File:Fluorite - Diana Maria mine, Rogerley quarry, Stanhope, County Durham, England.jpg|Fluorite from Diana Maria mine, Weardale, England, UK
File:FluoriteMaroc.jpg|Fluorite from El Hammam Mine, Meknès Prefecture, Meknès-Tafilalet Region, Morocco
File:Fluorite frog, length 8 cm arp.jpg|Toad carved in fluorite. Length 8&nbsp;cm (3&nbsp;in).
</gallery>

==See also==
*[[List of countries by fluorite production]]
*[[List of minerals]]
*[[Magnesium fluoride]] – also used in UV optics

==References==
{{USGS|title=Fluorspar|url=http://minerals.usgs.gov/minerals/pubs/commodity/fluorspar/myb1-2009-fluor.pdf}}
{{Reflist|30em}}

==External links==
{{Wikisource1911Enc|Fluor-spar}}
{{Commons category|Fluorite}}
*[http://www.spanishminerals.com/blog/?p=359 Educational article about the different colors of fluorites crystals from Asturias, Spain] {{Webarchive|url=https://web.archive.org/web/20150618113916/http://www.spanishminerals.com/blog/?p=359 |date=2015-06-18 }}
*[https://web.archive.org/web/20140209105809/http://www.ukminingventures.com/WeardaleMines.htm An educational tour of Weardale Fluorite]
*[https://web.archive.org/web/20060713041606/http://www.isgs.uiuc.edu/servs/pubs/geobits-pub/geobit4/geobit4.htm Illinois State Geologic Survey]
*[http://www.museum.state.il.us/exhibits/symbols/mineral.html Illinois state mineral]
*[https://www.britishmuseum.org/explore/highlights/highlight_objects/gr/t/the_barber_cup.aspx Barber Cup] and [https://www.britishmuseum.org/explore/highlights/highlight_objects/gr/t/the_crawford_cup.aspx Crawford Cup], related Roman cups at [[British Museum]]

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[[Category:Fluorite| ]]
[[Category:Cubic minerals]]
[[Category:Minerals in space group 225]]
[[Category:Evaporite]]
[[Category:Fluorine minerals]]
[[Category:Luminescent minerals]]
[[Category:Industrial minerals]]
[[Category:Symbols of Illinois]]