fluorite variety as they are often prominently displayed in museum galleries and mineral book photos. These dark purple or violet crystals are easily confused with amethyst (purple quartz), although fluorite’s distinctive crystal shape, four planes of cleavage, and its relative softness can distinguish the two.
Fluorite exhibits perfect cleavage in four directions to form octahedrons. It is most often found as a pore-filling void or vein deposit, so the fluorite crystals tend to occur as a distinct layer or series of layers lining the walls of what was originally a void in the rock.
One of fluorite’s more unusual properties is that it will fluoresce, or glow, under ultraviolet light. It was one of the first materials in which the phenomena of fluorescence was recognized and studied, and the term ‘fluorescence’ actually comes from the mineral name ‘fluorite’.
In Our Earth: The Geologic Importance of Fluorite
Fluorite primarily occurs as a pore-filling mineral in carbonate rocks (limestones and dolostones), as low temperature hydrothermal vein deposits associated with lead and silver ores, and less often as an accessory mineral in pegmatites and granites. It is sometimes even precipitated at hot springs.
Limestone and dolostone rocks through which low temperature hydrothermal fluids have moved may be particularly rich in fluorite. In the past, carbonate rocks of the Mississippi River Valley hosted some of the world’s richest fluorite deposits, but most of these have since been mined away. When fluorite occurs as a cavity fill in carbonate rocks it is usually associated with calcite, dolomite, anhydrite, gypsum and sulfur. In hydrothermal vein deposits, fluorite may be found with calcite, dolomite, barite, galena, sphalerite, and even silver ores.
In Our Society: The Economic Importance of Fluorite
The name ‘fluorite’ comes from the Latin word ‘fluere’ that means “to flow.” Fluorite melts easily and is used as a flux in the smelting of metallic ores. A ‘flux’ is a material used to help remove impurities from ore as it is refined into metal. As such, large amounts of fluorite are extensively used in open-hearth steel and steel enamelware production, the smelting of aluminum, as well as lead and antimony refining. It is also used in the manufacture of some types of glass, enamel, and porcelains.
The element fluorine has many uses in our industrial society, and fluorite is our major source of fluorine. Consequently large amounts of fluorite are used in the production of hydrofluoric acid and the manufacture of high-octane fuels, as well as the manufacture of flat panel displays and semiconductors. The first large scale manufacture of fluorine occurred during WWII, when it was used to separate and enrich the uranium needed for the Manhattan Project’s atomic bomb program. For better or worse, fluorine helped usher us into an atomic age and is still used to enrich uranium for nuclear power plants and weapons. Fluorine is also used to create a variety of non-reactive fluorocarbon resins that are used to line pipes, tanks and even cooking utensils. One of the latter is best known under the trade name of Teflon.
At one time, fluorite was also used in the manufacture of chlorofluorocarbons (CFC’s) that were used as refrigerants and in aerosol sprays, but more recently this use has been curtailed because of concerns over the role of CFC’s in the reduction of the Earth’s ozone layer. On a more beneficial side, fluorite is the source of fluoridated water and the fluoride compounds used in toothpaste and mouthwash that help to reduce dental cavities.
You might wonder exactly how fluoride treatments help prevent tooth decay and the answer lies in the effect of fluorine on another mineral called apatite. Apatite is a phosphate mineral that makes up much of our bones and teeth. When the bacteria that live in plaque on teeth are exposed to sugar, they produce weak acids that can dissolve some of the apatite present in enamel to create a porous tooth surface. If this process continues, eventually a ‘cavity’ forms. Apatite occurs in three main