CURRENTLY VIEWING: Fluorite
 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.
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.
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 in the crystal lattice.
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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