What is Fluorite?
Fluorite is an important industrial mineral composed of calcium and fluorine (CaF2). It is used in a wide variety of
chemical, metallurgical and ceramic processes. Specimens with exceptional diaphaneity and color are cut into gems or used to make ornamental objects.
Fluorite is deposited in veins by hydrothermal processes. In these rocks it often occurs as a gangue mineral associated
with metallic ores. Fluorite is also found in the fractures and cavities of some limestones and dolomites. It is a very
common rock-forming mineral found in many parts of the world. In the mining industry fluorite is often called "fluorspar."
Physical Properties of Fluorite
Fluorite is very easy to identify if you consider cleavage, hardness and specific gravity. It is the only common mineral
that has four directions of perfect cleavage, often breaking into pieces with the shape of an octahedron. It is also the
mineral used for a hardness of four in the Mohs Hardness Scale. Finally, it has a specific gravity of 3.2 which is detectably
higher than most other minerals.
Although color is not a reliable property for mineral identification, the characteristic purple, green and yellow translucent
to transparent appearance of fluorite is an immediate visual clue for the mineral.
Physical Properties of Fluorite
||typically purple, green and yellow. Also colorless, blue, red and black.
||transparent to translucent
||four directions of perfect cleavage
||cleavage, hardness, specific gravity, color
||Numerous uses in the metallurgical, ceramics and chemical industries. A source of fluorine, hydrofluoric acid, metallurgical flux. High clarity pieces are used to make lenses for microscopes, telescopes and cameras.
In 1852, George Gabriel Stokes discovered the ability of specimens of fluorite to produce a blue glow
when illuminated with light, which in his words was "beyond the violet end of the spectrum." He called
this phenomenon "fluorescence" after the mineral fluorite. The name gained wide acceptance in mineralogy,
gemology, biology, optics, commercial lighting and many other fields.
(See photo pair at right for an example of fluorite fluorescence in tumbled stones.)
*** Learn about Fluorescent Minerals ***
Fluorite typically glows a blue-violet color under short-wave ultraviolet and long-wave ultraviolet
light. Some specimens are known to glow a cream or white color. Many specimens do not fluoresce. Fluorescence
in fluorite is thought to be caused when trace amounts of yttrium, europium, samarium or other elements
substitute for calcium in the fluorite mineral structure.
Most fluorite occurs as vein fillings in rocks that have been subjected to hydrothermal activity. These veins
often contain metallic ores which can include sulfides of tin, silver, lead, zinc, copper and other metals.
Fluorite is also found in the fractures and vugs of some limestones and dolomites. Fluorite can be
massive, granular or euhedral as octahedral or cubic crystals. Fluorite is a common mineral in hydrothermal
and carbonate rocks worldwide.
Uses of Fluorite
Fluorite has a wide variety of uses. The primary uses are in the metallurgical, ceramics and chemical industries;
however, optical, lapidary and other uses are also important.
Fluorspar, the name used for fluorite when it is sold as a bulk material or in processed form, is sold in three different grades (acid, ceramic and metallurgical).
Acid Grade Fluorspar
Acid grade fluorspar is a high purity material used by the chemical industry. It contains over 97% CaF2.
Most of the fluorspar consumed in the United States is acid grade even if it is used in lower grade applications.
It is used mainly in the chemical industry to manufacture hydrofluoric acid (HF). The HF is then used to manufacture
a variety of products which include: fluorocarbon chemicals, foam blowing agents, refrigerants and a variety of
Ceramic Grade Fluorspar
Ceramic grade fluorspar contains between 85% and 96% CaF2. Much of this material is used
in the manufacture of specialty glass, ceramics and enamelware. Fluorspar is used to make glazes and surface
treatments that produce hard glossy surfaces, opalescent surfaces and a number of other appearances that make
consumer glass objects more attractive or more durable. The non-stick cooking surface known as Teflon is made using
fluorine derived from fluorite.
Metallurgical Grade Fluorspar
Metallurgical grade fluorspar contains between 60 and 85% CaF2. Much of this material is used in
the production of iron, steel and other metals. Fluorspar can serve as a flux that removes impurities such as
sulfur and phosphorous from molten metal and improves the fluidity of slag. Between 20 and 60 pounds of
fluorspar is used for every ton of metal produced. In the United States many metal producers use fluorspar that
exceeds metallurgical grade.
Optical Grade Fluorite
Specimens of fluorite with exceptional optical clarity have been used as lenses. Fluorite has a very low refractive
index and a very low dispersion. These two characteristics enable the lens to produce extremely sharp images. Today,
instead of using natural fluorite crystals to manufacture these lenses, high-purity fluorite is melted and combined with other
materials to produce synthetic "fluorite" lenses of even higher quality. These lenses are used in optical equipment such
as microscopes, telescopes and cameras.
Lapidary Grade Fluorite
Specimens of fluorite with exceptional color and clarity are often used by lapidaries to cut gemstones and make
ornamental objects. High-quality specimens of fluorite make beautiful faceted stones; however, the mineral is so
soft and cleaves so easily that these stones are either sold as collector's specimens or used in jewelry that
will not be subjected to impact or abrasion. Fluorite is also cut and carved into ornamental
objects such as small figurines and vases. These are often treated with a coating or impregnation to enhance their stability
and protect them from scratches.
Fluorite Production in the United States
Deposits of minable fluorite exist in the United States; however, nearly all of the fluorite consumed in
the United States is imported. The primary countries that supplied fluorite to the United States in 2011
were China, Mexico, Mongolia and South Africa. All of this fluorite is imported because production
costs in the United States are so high that the material can be produced in these other countries and
shipped directly to customers in the United States at a lower cost.
In 2011 several companies were producing and selling synthetic fluorite as a byproduct of their phosphoric acid
production, petroleum processing, or uranium processing activities. A limestone producer in Illinois was also
recovering and selling small amounts of fluorite from their quarry. That company is developing an underground
mine to exploit a large vein of fluorite which they hope will be in production in 2013.
Contributor: Hobart King
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|Fluorite is the only common mineral with four directions of perfect cleavage. This perfect cleavage combined with the mineral's isometric crystal structure frequently cause it to cleave into perfect octahedrons as shown here. These specimens also show the purple and yellow colors that are typical of fluorite. Photo by Hannes Grobe, used here under a creative commons license.
|Tumble-polished specimens of fluorite in normal light (top) and under short-wave ultraviolet light (bottom). The fluorescence appears to be related to the color and banding structure of the minerals in plain light.
|Illustration showing the relative size and position of fluorine and calcium ions in the isometric unit cell of fluorite. Public domain image by Benjah-bmm27.
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|Fluorite can be a beautiful gemstone when faceted. It is mainly a gemstone for collectors because it has a hardness of 4 on the Mohs scale and because it cleaves easily in four directions.
|Colorful pieces of fluorite can be cut into beautiful cabochons and other ornamental objects. However, because of its low hardness and perfect cleavage, it is not suitable for many purposes.