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60-511: Blue John (also known as Derbyshire Spar ) is a semi-precious mineral, a rare form of fluorite with bands of a purple-blue or yellowish colour. In the United Kingdom it is found only at Blue John Cavern and Treak Cliff Cavern at Castleton in Derbyshire . During the 19th century, it was mined for its ornamental value, and mining continues on a small scale. The most common explanation for

120-787: A combination of different types of glass; each type of glass 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 (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). The refractive qualities of fluorite and of certain flint elements provide

180-608: A constituent of sedimentary rocks either as grains or as the cementing material in sandstone . 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 tonnes (Mt) with the largest deposits being in South Africa (about 41 Mt), Mexico (32 Mt) and China (24 Mt). China

240-499: A few hours, a phenomenon apparently caused by the heat realigning the lattice dislocations removing the colour. Irradiating the discoloured Blue John in a nuclear reactor can bring the colour back. Blue, unbanded fluorite occurs in many localities around the world. Within the UK, blue fluorspars are also found in County Durham , especially Weardale . Elsewhere, blue fluorspar is known in

300-542: 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. The use of fluorite for prisms and lenses was studied and promoted by Victor Schumann near the end of the 19th century. Naturally occurring fluorite crystals without optical defects were only large enough to produce microscope objectives. With

360-449: A phenomenon usually only reported in synthetic materials. 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

420-416: A saw. They may be made into rough cuboids or cylinders ("rough-outs"), for turning as bowls and vases, or flat slices, for making jewellery. Rough-outs are glued to a metal chuck and turned on a lathe, sometimes using pieces of broken grinding wheels. The chuck is removed by heating the glue, or—if the operator is inclined—a sharp tap on the chuck with a spanner. A further resining stage may take place, before

480-414: A soft ornamental rock which they called murrhine , out of which drinking vessels were carved. Pliny describes the mineral as having a "great variety of colours" with "shades of purple and white with a mixture of the two". Whether this mineral was banded fluorite is uncertain, but it was apparently soft enough (like fluorite) to allow one particular man of consular rank to gnaw at the edges of his cup. There

540-465: A uniquely high transparency at this wavelength. Fluorite objective lenses are manufactured by the larger microscope firms (Nikon, Olympus , Carl Zeiss and Leica). Their transparence to ultraviolet light enables them to be used for fluorescence microscopy . The fluorite also serves to correct optical aberrations in these lenses. Nikon has previously manufactured at least one fluorite and synthetic quartz element camera lens (105 mm f/4.5 UV) for

600-409: Is a county in the prefecture-level city of Huzhou , in the northwest of Zhejiang province. As of 2020 census, its population was 548,568 all living in the built-up (or metro) area. Deqing is very close to Hangzhou and Shaoxing , so it is becoming de facto a suburb of the two cities. It is being conurbated soon and even a Metro Line is planned in the middle term to link both cities. Located in

660-475: Is a short story by Sir Arthur Conan Doyle , which appeared in The Strand Magazine of 1910 and describes the experiences of a doctor who, while recuperating from tuberculosis on a Derbyshire farm, investigates mysterious goings-on in a cavern mined for Blue John. Fluorite The Mohs scale of mineral hardness , based on scratch hardness comparison , defines value 4 as fluorite. Pure fluorite

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720-643: 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. One of

780-566: 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 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 chemicals . Optically clear transparent fluorite has anomalous partial dispersion , that is, its refractive index varies with

840-479: Is commonly present. The color of the fluorite is determined by factors including impurities, exposure to radiation, and the absence of voids of the color centers . 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 : The resulting HF is converted into fluorine, fluorocarbons , and diverse fluoride materials. As of

900-511: Is derived from the Latin verb fluere , meaning to flow . The mineral is used as a 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

960-533: Is kept within Castleton where small articles, mainly jewellery, are worked and sold. A "lost" deposit was rediscovered in Treak Cliff Cavern in 2013, and in 2015 a new vein, the first for 150 years, was discovered close to the tourist route in the same cavern. Elsewhere, similar blue and white-yellow banded fluorite ornaments are now imported into the UK and other countries from China. Before they can be worked,

1020-622: Is known that by this date the mining of Blue John had been going on for several years. The earliest dated decorative applications of Blue John in Britain are those in use as fireplace panels. The bridal suite of the Friary Hotel in Derby has a Blue John plaque dated to around 1760. About the same time, fireplaces with Blue John panels were designed by neoclassical architect and interior designer Robert Adam , and put in place at Kedleston Hall near Derby. By

1080-610: 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). One of the largest deposits of fluorspar in North America is located on the Burin Peninsula , 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

1140-602: Is nicknamed "Snake Village" by the media, and Deqing Snake Culture Museum is a local tourist attraction. Towns: Yunxiu Temple is a Buddhist temple in Xiazhuhu Subdistrict. Deqing has two railway stations, normal trains serve through Deqing West railway station , which located on the Xuancheng–Hangzhou railway , with fairly frequent, although not particularly fast, passenger service to Hangzhou and Hefei . High speed trains serve Deqing railway station , on

1200-473: Is no evidence that they encountered the Blue John veins. The earliest reference to the mineral "Blue John" occurs in a letter dated 1766 noting a lease from Lady Mazarine, which states that she "let ye Blue John, Castleton". The next reference occurs in a 1768 letter by the industrialist Matthew Boulton who attempted to purchase or lease the mines so that he could mine the Blue John to create decorative vases. It

1260-562: Is no reason to suppose the mineral came from Britain – Pliny and other writers specifically state that the mineral came from Persia . It is sometimes claimed that Blue John vases were found during excavations at Pompeii , but these vases are in fact made from banded amethystine quartz. However, two cups have been found among Roman grave-goods near the Turkish/Syrian border, on the former Persian-Roman trade route, which were made from blue-yellow banded fluorspar presumably obtained from

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1320-457: Is now thought that the colour may be a physical phenomenon due to crystal lattice dislocation . If the regular arrangement of atoms in the fluorite molecules are disturbed or dislocated, then this may yield the blue colour in Blue John. The cause of these dislocations is unknown, but one possibility is that it is due to colloidal calcium, i.e. excess of calcium atoms needed to form fluorite. Blue John can be decolourised by heating it in an oven for

1380-463: Is renowned as a center of snake farming . The locals have been raising snakes since the 1980s; currently, about 800 people in Zisiqiao work in snake farming industry, raising some three million snakes a year. Live snakes are supplied to specialty restaurants; dried or preserved in alcohol , they are sold to manufacturers of traditional Chinese medicines ; snake-infused wine is made as well. The village

1440-618: Is so common that the motif is called the fluorite structure . Element substitution for the calcium cation often includes strontium and certain rare-earth elements (REE), such as yttrium and cerium . Fluorite forms as a late-crystallizing mineral in felsic igneous rocks typically through hydrothermal activity. It is particularly common in granitic pegmatites. It may occur as a 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

1500-631: Is the Deqing Fluorite Mine, in Deqing County , Zhejiang Province, the only source (other than in Derbyshire) that has an ornamental craft based upon it. However, although this fluorite is similar to Blue John its banding is straighter and it contains colours not associated with Blue John, suggesting they are compounds and not inclusions as in Blue John. Roman writers, such as Pliny the Elder , refer to

1560-683: 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 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 and flint glass elements to make an achromatic lens . Optical groups employ

1620-671: The Ardennes region of Belgium; the Cave-in-Rock area of Illinois in the United States; and at various localities in Mexico and China. Blue-banded fluorite is very rare. An ornamental mineral known to the Romans as murrhine may have been a fluorspar similar to Blue John. Recently discovered deposits in China have produced fluorite with colouring and banding similar to the classic Blue John stone. One source

1680-561: The Cornish language word bleujenn , in Old Cornish blodon , a flower, bloom or blossom. In the United Kingdom, the blue, banded fluorite known as Blue John is found only under the triangular hill known as Treak Cliff, just outside the village of Castleton . Today the veins are mined only in Blue John Cavern and the nearby Treak Cliff Cavern , although the abandoned Old Tor Mine on

1740-557: The 1760s. An alternative origin of the name derives from an old miners' name for the zinc ore sphalerite , which they called "Black Jack". Thus, the unique blue stone mined in these caverns could easily have become known as "Blue John". Another derivation comes from the Cornish miners who began working the Derbyshire lead mines in the 1740s. The name "Blue John" is used for several rocks in Cornwall , including fluorspars, and derives from

1800-462: 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. Exposure tools for the semiconductor industry make use of fluorite optical elements for ultraviolet light at wavelengths of about 157 nanometers . Fluorite has

1860-410: The 19th century Blue John was being fashioned into a wide variety of ornamental items ranging from knife-handles to chalices. The precise quantities mined in any given year are unknown, but 18th-century leases restricted output to 20 tons per annum. By 1892, the output is said to have been limited to 3 tons per annum. Today, production is probably around half a ton per annum, and the raw Blue John produced

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1920-463: The Blue John, like fluorite elsewhere in the Peak District, crystallised from a highly saline fluid at temperatures of 90–120 °C or perhaps a little higher. Despite much investigation, the origin of the blue colour of Blue John remains uncertain. Microscopic analysis has failed to find any impurities such as potassium permanganate or hydrocarbons which could produce a purple-blue colour. It

1980-497: The Latin terms murrina and myrrhina refer to fluorite. 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. Fluorite crystallizes in a cubic motif . Crystal twinning is common and adds complexity to the observed crystal habits . Fluorite has four perfect cleavage planes that help produce octahedral fragments. The structural motif adopted by fluorite

2040-769: The Persian source mentioned by Pliny. Both cups, known as the Crawford Cup and the Barber Cup , are in the British Museum . It is sometimes said that Blue John of Derbyshire was discovered by the Romans. However, the earliest source of this story is William Adam's 1843 book Gem of the Peak . It seems likely that Adam was attempting to add some mystique to the Derbyshire Blue John. Although the Romans did mine lead in Derbyshire, there

2100-401: The addition of AlF 3 , the majority of which react with excess sodium from the alumina to form Na 3 AlF 6 . 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

2160-450: 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 magnifications . Canon Inc. produces synthetic fluorite crystals that are used in their better telephoto lenses . The use of fluorite for telescope lenses has declined since

2220-428: 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. Natural samples containing rare earth impurities such as erbium have also been observed to display upconversion fluorescence , in which infrared light stimulates emission of visible light,

2280-405: The classic Blue John stone. George Gabriel Stokes named the phenomenon of fluorescence from fluorite, in 1852. Many samples of fluorite exhibit fluorescence under ultraviolet 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 ultraviolet light, followed by

2340-523: 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, 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. Cubic crystals up to 20 cm across have been found at Dalnegorsk , Russia. The largest documented single crystal of fluorite

2400-557: 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

2460-421: The fluorite with sulfuric acid . Internationally, acid-grade fluorite is also used in the production of AlF 3 and cryolite (Na 3 AlF 6 ), which are the main fluorine compounds used in aluminium smelting. Alumina is dissolved in a bath that consists primarily of molten Na 3 AlF 6 , AlF 3 , and fluorite (CaF 2 ) to allow electrolytic recovery of aluminium. Fluorine losses are replaced entirely by

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2520-429: The late 1990s, five billion kilograms were mined annually. 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 2 ), 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

2580-650: The middle of the plain between the Hangzhou Bay and the Taihu , most of Deqing County is flat, criss-crossed by numerous canals. The western end of the county is mountainous. There, the popular tourist areas of Moganshan (莫干山) is located. Moganshan is a scenic mountain, an hour from Hangzhou , with many pre-World War II villas built by foreigners, along with one of Chiang Kai-shek 's Guomindang compounds. Zisiqiao ( 子思桥 ) Village, located within Deqing County's Xinshi Town ,

2640-598: 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 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 . Recently discovered deposits in China have produced fluorite with coloring and banding similar to

2700-466: The name is that it derives from the French bleu-jaune , meaning 'blue-yellow'. The story goes that Blue John was exported to France where it was used by ormolu workers during the reign of Louis XVI (1774–92). However, there is no archival record of any Blue John being exported to France, and the early ormolu ornaments which use Blue John were being manufactured by Matthew Boulton of Birmingham in

2760-513: The nature of metals], by Georgius Agricola , as a mineral noted for its usefulness as a flux. Agricola, a German scientist with expertise in philology , mining , and metallurgy, named fluorspar as a Neo-Latinization of the German Flussspat from Fluss ( stream , river ) and Spat (meaning a nonmetallic mineral akin to gypsum , spærstān, spear stone , referring to its crystalline projections). In 1852, fluorite gave its name to

2820-504: The north side of Winnats Pass was also, at one time, a source for the mineral. The mineral veins of the Peak District were formed during the late Carboniferous and Early Permian times, when the limestones were at a depth of 3 kilometres (1.9 mi). The minerals were deposited in veins by layers of crystals precipitating from hot fluids coating the walls of fractures, caves, and other cavities. Petrological analysis has shown that

2880-438: 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 . 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,

2940-434: The piece is returned to the lathe and polished with wet abrasive paper. A final high polish is added using putty powder (finely crushed tin dioxide ) applied with a moist piece of felt. For making jewellery, thin slices are marked out and cut into shapes such as circles or ovals, then finished on a grinding wheel. The rear faces of single-sided pieces are painted white before they are mounted. " The Terror of Blue John Gap "

3000-782: The production of ultraviolet images . Konica produced a fluorite lens for their SLR cameras – the Hexanon 300 mm f/6.3. 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. 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

3060-433: 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,

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3120-512: The property of thermoluminescence . 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

3180-592: 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 and other manufacturers have used synthetically grown crystals of calcium fluoride components in lenses to aid apochromatic design, and to reduce light dispersion . This use has largely been superseded by newer glasses and computer-aided design. As an infrared optical material, calcium fluoride

3240-444: The removal of impurities, and later in the production of aluminium . Ceramic grade fluorite (85–95% CaF 2 ) is used in the manufacture of opalescent glass , enamels , and cooking utensils. The highest grade, "acid grade fluorite" (97% or more CaF 2 ), accounts for about 95% of fluorite consumption in the US where it is used to make hydrogen fluoride and hydrofluoric acid by reacting

3300-499: The stone's zonation. 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 0.15 μm to 9 μm) 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 nm, a common wavelength used for semiconductor stepper manufacture for integrated circuit lithography ,

3360-410: The stones (having been air-dried for at least a year) are heated in an oven, then placed in a bowl of hot epoxy resin (previously, pine resin was used), and then further heated in a vacuum oven. This drives out air from minute pores in the stone, and replaces it with the resin, which binds the otherwise friable crystal structure, allowing it to be cut and polished. After resining, the stones are cut on

3420-550: 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 NMR carried out on the gas contained in the antozonite, revealed a peak at 425 ppm, which is consistent with F 2 . [REDACTED]  This article incorporates public domain material from Fluorspar (PDF) . United States Geological Survey . Deqing County, Zhejiang Deqing ( Chinese : 德清县 ; pinyin : Déqīng Xiàn )

3480-420: The wavelength of light in a manner that differs from that of commonly used glasses, so fluorite is useful in making 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. The word fluorite

3540-597: 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 970 feet (300 m). In the St. Lawrence area, the veins are persistent for great lengths and several of them have wide lenses . The area with veins of known workable size comprises about 60 square miles (160 km ). In 2018, Canada Fluorspar Inc. commenced mine production again in St. Lawrence; in spring 2019,

3600-437: Was a cube 2.12 meters in size and weighing approximately 16 tonnes. 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

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