Fluorite

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Fluorite
Missing image
Fluorite_China.jpg
Cubic fluorite crystals from China
General
CategoryMineral
Chemical formulacalcium fluoride CaF2
Identification
Color White or colorless, purple, blue, blue-green, yellow, brownish-yellow, or red.
Crystal habit Occurs as well-formed coarse sized crystals also massive - granular.
Crystal system Isometric 4/m bar 3 2/m.
Cleavage [111] Perfect, [111] Perfect, [111] Perfect.
Fracture Uneven.
Mohs Scale hardness 4
Luster Vitreous.
Refractive index 1.433-1.435
Pleochroism -
Streak White.
Specific gravity 3.18
Fusibility 3
Solubility Slighty in water.
Other sometimes phosphoresces when heated or scratched. Other varieties fluoresce beautifully.
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Fluorite_USA.jpg
Octahedral fluorite crystals from New Mexico, USA

Fluorite (also called fluor-spar) 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.

Contents

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.

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Fluorite_crystals_270x444.jpg
Cleaved fluorite octahedra.

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. In the United States deposits are found in Missouri, Oklahoma, Illinois, Kentucky, Colorado, New Mexico, Arizona, Ohio, New Hampshire, and New York.

Fluorescence

Fluorite gives its name to the property of Fluorescence, as many samples fluoresce strongly in ultra-violet light. The fluorescence may be due to impurities such as yttrium in the crystal lattice.

Blue John

One of the most famous of the older localities of fluorite is Castleton, Derbyshire, England, where under the name of Derbyshire Blue John beautiful purple-blue fluorite was used for ornamental purposes, especially in the 19th Century. It is now scarce, and only a few hundred kilograms are mined each year for ornamental and lapidary use. Recent deposits in China have produced fluorite with similar colouring and banding to the classic Blue John stone.

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USDA_Mineral_Flourite_93c3962.jpg
Mineral fluorite

Uses

As well as ornamental uses, fluorite is also used as a flux in the manufacture of steel, in the making of opalescent glass, enamels for cooking utensils, and for hydrofluoric acid. Fluorite is also used in some high performance telescopes and camera lens elements instead of glass. It 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. Most optical material is now synthetic. The name fluorite is derived from the Latin fluo, flow, in reference to its use as a flux. Fluorite is slightly soluble in water, and is decomposed by sulfuric acid and forms free hydrofluoric acid.

See also: List of minerals

References

  • Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, pp. 324 - 325, 20th ed., ISBN 0471805807
  • Mineral Galleries (http://mineral.galleries.com/minerals/halides/fluorite/fluorite.htm)
  • Webmineral (http://webmineral.com/data/Fluorite.shtml)
  • Mindat.org (http://www.mindat.org/min-1576.html)
  • Illinois state mineral (http://www.museum.state.il.us/exhibits/symbols/mineral.html)

Gallery

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es:Fluorita fr:Fluorite nl:Vloeispaat ja:蛍石 pl:Fluoryt

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