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Fluorite (also called fluorspar) is a halide 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. Crystal twinning
is common and adds complexity to the observed crystal habits.
Detaild description
The
word fluorite is derived from the Latin
root fluo, meaning "to flow" because the mineral has a
relatively low melting point and was used as an important flux in smelting.
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.[2]
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Occurrence
Fluorite
may occur as a vein deposit, especially with metallic minerals, where it often
forms a part of the gangue (the surrounding "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 China, Germany, Austria, Switzerland, England, Norway, Mexico, and both Ontario and Newfoundland 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. Fluorite has been the state mineral of Illinois since 1965. At that time, Illinois was
the largest producer of fluorite in the United States; however, the last
Illinois mine closed in 1995.[5]
The
world reserves of fluorite are estimated at 230 million tonnes with the largest
contributors being South Africa (42 million tonnes), Mexico (32 million tonnes)
and China (21 million tonnes). China is leading the world production with 3
million tonnes (2009 data) followed by Mexico (0.925 million tonnes), Mongolia
(0.28 million tonnes) and Russia (0.21 million tonnes).[6]
One
of the largest deposits of fluorspar in North America is located in 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 fluorite 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 970 feet. In 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.[7][8][9]
Cubic
crystals up to 20 cm across have been found at Dalnegorsk, Russia.[10] The largest documented single crystal
of fluorite was a cube 2.12 m in size and weighed ~16 tonnes.[11]
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 both
the Blue John Cavern and the nearby Treak Cliff Cavern.[12]
Recently
discovered deposits in China have produced fluorite with coloring and banding
similar to the classic Blue John stone.[13]
Fluorescence
Many
samples of fluorite fluoresce under ultra-violet light, a property that takes its
name from fluorite[14]. 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 mineral
impurities such as yttrium, ytterbium, or organic matter in the crystal
lattice. In particular, the blue fluorescence seen in fluorites from certain
parts of England responsible for the naming of the phenomenon of fluorescence itself, has been attributed to the
presence of inclusions of divalent europium in the crystal.[15]
The
color of visible light emitted when a sample of fluorite is fluorescing is
dependent 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
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 fluorite from Yorkshire, Derbyshire, and Cornwall, if they fluoresce at all, are generally
only feebly fluorescent.
Fluorite
also exhibits the property of thermoluminescence.[16]
Color
Fluorite
comes in a wide range of colors and has subsequently been dubbed "the most
colorful mineral in the world". The most common colors are purple, blue,
green, yellow, or colorless. Less common are pink, red, white, brown, black,
and nearly every shade in between. Color zoning or banding is commonly present.
The color of the fluorite is determined by factors including impurities,
exposure to radiation, and the size of the color centers.
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. Ceramic (intermediate) grade fluorite
is used in the manufacture of opalescent glass,
enamels and cooking utensils. 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. The highest grade, acid grade
fluorite (97% or more of CaF2), is used to make hydrofluoric acid by decomposing the fluorite with
sulfuric acid. Hydrofluoric acid is the primary
feedstock for the manufacture of virtually all organic and inorganic
fluorine-containing compounds, including fluoropolymers and perfluorocarbons, and is also used to etch glass.[17]
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
optical elements for ultraviolet light
at 157 nm wavelength. Fluorite has a
uniquely high transparency at this wavelength. Fluorite has a very low dispersion so
lenses made from it exhibit less chromatic aberration
than those made of ordinary glass.[18] In telescopes it allows crisp images
of astronomical objects even at high power. Fluorite also has ornamental and lapidary uses. 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.[19] The fluorite also serves to correct optical aberrations
in these lenses. Canon Inc. produces
synthetic fluorite crystals that are used in their more expensive telephoto lenses. Nikon
has previously manufactured at least one all-fluorite element camera lens
(105 mm f/4.5 UV) for the production of ultraviolet images.[20]
Fluorine (pronounced /ˈflʊəriːn/,
/ˈflʊərɨn/, or /ˈflɔr-/) is the chemical element with atomic number 9, represented by the symbol F. Fluorine forms a single bond with itself in elemental form, resulting
in the diatomic F2 molecule. F2 (fluorine) is a supremely
reactive, poisonous, pale, yellowish brown gas. Elemental
fluorine is the most chemically reactive and electronegative of all the elements. For example,
it will readily "burn" hydrocarbons at room temperature, in contrast to
the combustion of hydrocarbons by oxygen, which requires an input of energy
with a spark. Therefore, molecular fluorine is highly dangerous, more so than
other halogens such as the poisonous chlorine gas.
Fluorine's
highest electronegativity and small atomic radius give unique properties to
many of its compounds. For example, the enrichment of 235U, the principal nuclear fuel, relies on the
volatility of UF6.
Also, the carbon–fluorine bond
is one of the strongest bonds in organic chemistry. This contributes to the
stability and persistence of fluoroalkane based organofluorine
compounds, such as PTFE/(Teflon) and PFOS.
The carbon–fluorine bond's inductive effects result in the strength of many
fluorinated acids, such as triflic acid and trifluoroacetic acid.
Drugs are often fluorinated at biologically reactive positions, to prevent
their metabolism and prolong their half-lives.
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