Fluorite (also called fluor-spar or Blue John) is a mineral composed of calcium fluoride, CaF₂. It is an isometric mineral with a cubic habit, though octohedrons and dodecahedrons are not uncommon.

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 constituent of dolostone and limestone.

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.

Blue John

One of the most famous of the older localities of fluorite is Derbyshire, England, where under the name of Derbyshire Blue John beautiful blue fluorite is used for ornamental purposes. Its softness, however, has been a bar to general use.

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

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
• Webmineral
• Mindat.org
• Illinois state mineral