Fluorite

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Fluorite

Cubic fluorite crystals from China
General
Category Mineral
Chemical formula calcium fluoride CaF2
Identification
Color White or colorless, purple, blue, blue-green, green, yellow, brownish-yellow, pink, 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
Refractive index 1.433-1.435
Streak White
Specific gravity 3.18
Fusibility 3
Solubility Slightly in water
Other Characteristics sometimes phosphoresces when heated or scratched. Other varieties fluoresce beautifully

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. Crystal twinning is common and adds complexity to the observed crystal habits.

Contents

[edit] 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 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, New York, and Texas. Illinois has historically been the largest producer of fluorite in the United States, however, the last of the mines closed in 1995.[1] The Illinois general assembly passed a resolution in 1965 declaring Fluorite as the official state mineral.

[edit] 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 or organic matter in the crystal lattice.

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.

[edit] Blue John

Blue John veins in the Blue John Cavern,UK
Enlarge
Blue John veins in the Blue John Cavern,UK

One of the most famous of the older localities of fluorite is Castleton in Derbyshire, England, where, under the name of Derbyshire Blue John, beautiful purple-blue fluorite was used for ornamental purposes, especially in the 19th century. The name derives from French "bleu et jaune" (blue and yellow) characterising its colour. 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.

[edit] Uses

As well as ornamental uses, fluorite is used in the making of opalescent glass, enamels cooking utensils, hydrofluoric acid, and as a flux in the manufacture of steel. Fluorite is also used in some high performance telescopes and camera lens elements instead of glass. Exposure tools for the semiconductor industry, make the 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. 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. The name fluorite is derived from the Latin fluo, meaning "flow", in reference to its use as a flux. Fluorite is slightly soluble in water, and is decomposed by sulfuric acid to form free hydrofluoric acid, which etches glass.

[edit] See also

[edit] References

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[edit] Gallery

Pig carved in fluorite, 5 cm (2 inches) long

Mineral fluorite

Octahedral fluorite crystals from New Mexico, USA

Cleaved fluorite octahedra

The unit cell of fluorite's crystal structure
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