Fluorite

Mineral Name: Fluorite

Chemical Composition: CaF2

Color: The possible fluorite colors come in a variety, but common colors are purple, yellow, and green. Also, at times can be colorless, black, blue, and red. (3)

Streak: The streak of fluorite is white. (1)

Hardness: According to Moh’s Scale of Hardness, fluorite has a hardness of 4. This means it will scratch a penny, but isn’t strong enough to scratch a nail. (1)

Cleavage/Fracture: Fluorite is a unique mineral when it comes to its cleavage due to its four directions of perfect cleavage, something not seen many common minerals. The shape of fluorite often resembles an octahedron. (3)

Crystal Form: Fluorite crystals are equal in dimension because they have an isometric crystal habit. Fluorite typically takes on a cubic form, although other complex forms are not uncommon. A combination of octahedral, cubes, and dodecahedral growths could also be present (7). Fluorite that forms in high temperature liquids usually form as octahedral crystals. Fluorite that forms in low temperature liquids form cubic crystals (5). Often times two separate crystals can come together in a symmetrical manner to share the same crystalline lattice. These shared lattices are referred to as twinning. Twinning adds complexity to the observable crystal behavior. (5)

Luster: Fluorite is vitreous in luster, which means it shows a glass-like surface. (4)

Special Features: Fluorite glows a blue color when placed under an ultraviolet light. (2) (4)

Varieties: There are several varieties of fluorite that exist. Antozonite is a variety that gives off an odor when broken. Blue John is a variety of banded purple and white fluorite. Chlorophane is a variety that gives off a bright green hue when heated. And lastly, there is Yttrocerite and Yttrofluorite, which are two varieties where some of the lattice’s calcium ions are replaced with either yttrium or yttrium and cerium. (1)

Mineral Group: Fluorite belongs to the halide mineral group. (1) Halides require chlorine, fluorine, bromine or iodine as the main anion. (7)

Environment: Fluorite is commonly found in mineral deposit of hydrothermal ores, sedimentary deposits, metamorphic environments, and granite pegmatite dikes. (4) Fluorite can be found as a cavity in hydrothermal vein deposits with minerals such as sphalerite, barite, galena, calcite, and dolomite. (4) In these cases many time fluorite is considered a gangue mineral, and ore deposits are usually mixed in with valueless unwanted rocks called gangue minerals. (10)

Associated Rock types: Two specific rocks that contain fluorite are limestone and dolostone, specifically when these rocks have had low temperature hydrothermal fluids moving through them during formation. (4) Fluorite appears as a cavity fill in these carbonate rocks with such minerals as calcite, dolomite, sulfur, gypsum, and anhydrite.

Occurrence in North America: Illinois passed a resolution declaring it the official state mineral. The state was historically the largest producer of fluorite in the U.S.A., until the last mine was closed down 30 years later. (5) Other occurrences in Missouri, Oklahoma, Kentucky Colorado, New Mexico, Arizona, Ohio, New Hampshire, New York, and Texas. (5)

Economic Uses and Industrial Uses: There are several economic and industrial uses of fluorite. Fluorite is considered a main source of the chemical element fluorine because there is such an abundance of it in fluorite. Fluorine has many uses including it presence in hydrofluoric acid for the production of high octane fuels, flat panel displays and semiconductors. (4) It is also used in the production of specialty glasses, ceramics and enamelware as well as Teflon. If the fluorite has exceptional optical clarity, it may be used in the production of lenses. Fluorite has a very low refractive index and a very low dispersion which enables the lense to produce extremely sharp images. (3)

The most notable significance to people is probably in the use of fluoride found in toothpaste. It has also been introduced into municipal water systems to serve as an aid in cavity reduction for people who consume the water. The way this is implemented is through a process in which one of three types of compounds, sodium fluoride, fluorosilicic acid or sodium fluorosilicate, is added to the water at treatment facilities. The most commonly used compound is fluorosilicic acid. It is a liquid byproduct of phosphate fertilizer manufacturing and is the most inexpensive. Water fluoridation also occurs naturally in groundwater in areas where there are “alkaline volcanic, hydrothermal, sedimentary and other rocks produced by highly evolved magmas and hydrothermal solutions”. (8) These areas contain high concentrations of fluorine that dissolves into nearby water sources as fluoride.(8)

It is also widely used in the metal manufacturing community as a flux. Flux is a material that is used to react with any oxides that might try to form during the refining of metals. It is used in open hearth steel and steel enamelware production as well as aluminum smelting and lead and antimony refining.(9) Fluorine was used during WWII for separating and enriching the uranium needed for the Manhattan Project’s atomic bomb program and is still used today to enrich uranium for nuclear power plants and weapons. (4)

First Notable Identification: There is not much information regarding the first findings of fluorite; however, it was first discussed in print in 1530 where it was termed fluorspar by a man named Georgius Agricola who noted the mineral for it’s usefulness as a flux (6). It is noted in some Roman texts that they mined a crystalline variety of fluorite that was later known as Blue John (6). The Romans also wrote about a soft ornamental rock, which they called murrhine, for use in the manufacture of vases and drinking cups. While the properties were very similar to fluorite, there is no certainty that it actually was. (6)

How We Identified It: We mainly used the hardness scale to identify it, that it is harder than a penny but softer than a nail. Its unique colors and ability to glow under UV light are also distinctive traits. Also, fluorite has four perfect directions of cleavage making it easy to identify.

Don’t Confuse It With: Fluorite is commonly confused with Quartz, Halite, and Calcite. (4) However, its hardness, taste and cleavage should differentiate it easily.