Fluorite

From New World Encyclopedia
Fluorite
Fluorite China.jpg
Cubic fluorite crystals from China
General
CategoryMineral
Chemical formulacalcium fluoride CaF2
Identification
ColorWhite or colorless, purple, blue, blue-green, green, yellow, brownish-yellow, pink, or red
Crystal habitOccurs as well-formed coarse sized crystals also massive - granular
Crystal systemIsometric 4/m bar 3 2/m
Cleavage[111] Perfect, [111] Perfect, [111] Perfect
FractureUneven
Mohs Scale hardness4
Refractive index1.433-1.435
StreakWhite
Specific gravity3.18
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Fusibility3
SolubilitySlightly in water
Other Characteristicssometimes phosphoresces when heated or scratched. Other varieties fluoresce beautifully

Fluorite (also called fluorspar) is a mineral found in large deposits in many parts of the world. Chemically, it is composed of calcium fluoride (chemical formula CaF2).

The name fluorite is derived from the Latin word fluo, meaning "flow," in reference to its use as a flux.

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 widely distributed around the world. 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, New York, and Texas.

Illinois has historically been the largest producer of fluorite in the United States. In 1965, the Illinois General Assembly passed a resolution declaring fluorite as the official state mineral. Yet, 30 years later, the last of the mines in Illinois was closed down.[1]

Blue John

Blue John veins in the Blue John Cavern, United Kingdom.

One of the most famous sites for the excavation of fluorite has been the Blue John Cavern in Castleton, Derbyshire, England. This site has yielded beautiful, purple-blue fluorite, under the name Derbyshire Blue John, which was used for ornamental purposes, especially in the nineteenth century. The name "Blue John" derives from the French words "bleu et jaune" (blue and yellow), characterizing its colors. This site is now depleted, and only a few hundred kilograms (kg) are mined each year for ornamental and lapidary use. Recently, deposits in China have produced fluorite with similar coloring and banding to the classic Blue John stone.

Characteristics

Fluorite 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.

Light dispersion through fluorite is very low, compared to dispersion through ordinary glass.

Fluorescence

Fluorite gives its name to the property of fluorescence, as many samples fluoresce strongly in ultraviolet light. The fluorescence may be due to impurities such as yttrium or organic matter in the crystal lattice.

Yet, not all fluorites fluoresce, even from the same locality, so UV lighting is not a reliable tool for identification of specimens, or for quantifying the mineral in mixtures. For example, among British fluorites, those from Northumberland, Durham and Eastern Cumbria are the most consistently fluorescent. Those from Yorkshire, Derbyshire and Cornwall are generally either not fluorescent, or feebly fluorescent.

Fluorite's fluorescence color is largely dependent on where the original specimen was located. Blue is the most common color but red, purple, yellow, green and white also occur. Fluorite also exhibits the property of thermoluminescence.

Uses

File:Fluorite galena09.jpg
Deep purple cubes of fluorite with galena (gray) and calcite (white) from Illinois.

In addition to ornamental uses, fluorite is used in manufacturing opalescent glass, enamels, cooking utensils, hydrofluoric acid, and as a flux in the manufacture of steel. Fluorite is also 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 for 157 nm wavelength. This wavelength is created by an excimer laser with F2 gas, and the fluorite is a unique material that has high transparency at this wavelength. Given the low dispersion of light through fluorite, this mineral is used in telescopes to produce crisp images of astronomical objects even at high power. Fluorite is slightly soluble in water, and reacts with sulfuric acid to form hydrofluoric acid, which etches glass.

See also

Notes

References
ISBN links support NWE through referral fees

  • Farndon, John. 2006. The Practical Encyclopedia of Rocks & Minerals: How to Find, Identify, Collect and Maintain the World's best Specimens, with over 1000 Photographs and Artworks. London: Lorenz Books. ISBN 0754815412 and ISBN 978-0754815419.
  • Mineral Gallery. 2006. Fluorite. Amethyst Galleries. Retrieved April 9, 2007.
  • Webmineral. Fluorite. Retrieved April 9, 2007.
  • Mindat.org. Fluorite. Mindat.org. Retrieved April 9, 2007.

External links

Gallery

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