Fluorite

What is fluorite?

Fluorite (also known as Fluorspar) 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 colour 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."
Fluorite is a colourful mineral, both in visible and ultraviolet light, and the stone has ornamental and lapidary uses. Industrially, fluorite is used as a flux for smelting, and in the production of certain glasses and enamels. The purest grades of fluorite are a source of fluoride for hydrofluoric acid manufacture, which is the intermediate source of most fluorine-containing fine chemicals. Optically clear transparent fluorite lenses have low dispersion, so lenses made from it exhibit less chromatic aberration, making them valuable in microscopes and telescopes. Fluorite optics are also usable in the far-ultraviolet range, where conventional glasses are too absorbent for use.

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 colour 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.

Fluorescence

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.
Fluorite typically glows a blue-violet colour under short-wave ultraviolet and long-wave ultraviolet light. Some specimens are known to glow a cream or white colour. 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.

Fluorite Occurrence

Most fluorite occurs as vein fillings in rocks that have been subjected to hydrothermal activity. These veins often contain metallic ores which can include sulphides 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 fluoride chemicals.

Ceramic Grade Fluorspar

Ceramic grade fluorspar contains between 85% and 96% CaF2. Much of this material is used in the manufacture of specially 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 sulphur 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 colour 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 jewellery 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 mineable 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.

Properties of Fluorite

Chemical FormulaCaF2
ColourWhite, Colorless, Blue, Red, Green, Yellow, Orange, Brown, Pink, Purple, Black, Banded, Multicoloured
Hardness4
Crystal SystemIsometric
Refractive Index.434
SG3.0 - 3.3
TransparencyTransparent to translucent
Double RefractionNone
LusterVitreous
Cleavage1, all sides
Mineral ClassFluorite