Fluorite
| Fluorite | |
|---|---|
 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.
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, 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 or organic matter in the crystal lattice.
Fluorite fluorescence colour is largly dependent of where the origional specimen was located. Blue is the most common colour but red, purple, yellow, green and white also occur. Fluorite also exhibits the property of thermoluminescence.
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.
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.
Gallery
 Pig carved in fluorite, 5 cm (2 inches) long |
 Mineral fluorite |
 Octahedral fluorite crystals from New Mexico, USA |
 Cleaved fluorite octahedra. |