Fluorite

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Fluorite
Image:Fluorite China.jpg Cubic fluorite crystals from China
General
Category	Mineral
Chemical formula	calcium 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.

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.

1 Occurrence
- 1.1 Fluorescence
- 1.2 Blue John
2 Uses
3 See also
4 References
5 Gallery

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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 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.

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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.

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Blue John

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.

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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.