Fluorite (also known as 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.
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
Chemical Classification	halide
Color	typically purple, green and yellow. Also colorless, blue, red and black.
Streak	white
Luster	vitreous
Diaphaneity	transparent to translucent
Cleavage	four directions of perfect cleavage
Mohs Hardness	4
Specific Gravity	3.2
Diagnostic Properties	cleavage, hardness, specific gravity, color
Chemical Composition	CaF2
Crystal System	isometric
Uses

 

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. (See photo pair at right for an example of fluorite fluorescence in tumbled stones.)

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 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.

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.