Fluorite, Calcium Fluoride, CaF2
Jamison Brizendine,
Economic Importance:
GEOS 350, Mineralogy
Fluorite has many industrial and practicable uses.
Fluorite is used as a component in iron and aluminum
smelting, special fluxes in welding rods, toothpastes,
ceramics. and optics. One of the most widely used organic
fluoride compounds, the refrigerant Freon 12®, is no
longer produced in the United States. The chlorine in the
compound is thought to damage the protective ozone layer
that shields the earth from ultraviolet radiation.
Department of Geosciences
Brizeja@earlham.edu
Fluorite in a Nutshell:
Color: Green, purple, blue, orange, red, yellow, and clear.
Hardness of 4, scratches Calcite, but can be scratched by Apatite. Fluorite is the ideal
mineral for it’s hardness.
Upper Left: Minerva #1 Mine, Cave-In-Rock, Illinois, www.mineralauctions.com
Luster: Vitreous
Up: Okarusu Mine, Otjiwarongo, Namibia: www.mineral-auctions.com
Upper Right: Boltburn Mine, Weardale, England:
Ukminingventures.com
Streak: White
Right: Blackdene Mine, Weardale, England: Ukminingventures.com
Cleavage: Perfect octahedral cleavages in four directions, and typically forms cubes,
octahedra and rarely dodecahedrons.
Specific Gravity: 3.1
Class: Halide,
Dana Number: 9.2.1.1
Common Impurities: Y, Ce, Si, Al, Fe, Mg, Eu, Sm
Point Group: 4/m 3bar 2/m
Optical Data: Isometric, n=1.433
Both the element Fluorine and the term “Fluorescence” comes from Fluorite. Fluorine
was successfully isolated by separating the Calcium from the Fluorine.
The deposits in Illinois, where the majority of commercial Fluorite is mined,
were formed as hot water flowed up into the competent limestones layers, which
are below a sandstone formation. Mineral deposits formed in this manner are called
hydrothermal deposits. The hot water flowed up along weak areas in the rocks of
this area. These weak areas are associated with the faults of the Wabash and
Reelfoot rift zones. These two rift zones are also responsible for earthquakes such as
the famous series of quakes at New Madrid, Missouri. The southern Illinois fluorite
deposits were probably formed between 100 and 250 million years ago.
The name Fluorite comes from the Latin word, “fluere”, which means, “to flow”.
Two Fluorine cations replaces the Carbonate cation (CO3) in Calcite, which
then creates Fluorite. It can also form during normal faulting and fluid fills the
cracks. Fluorite also forms with Spinel and Calcite in hornfels, high temperature
granties and other similar contact metamorphic rocks. Another environment that
Fluorite is found with are epithermal veins with barite and galena, but the most
common are the lode hydrothermal veins with zinc and lead.
Fluorine is often found with Pyrite, Sphalerite, Calcite, Quartz, Dolomite,
Chalcopyrite, Galena and Barite.
The map below shows the area where Fluorite is most commonly found in the
United States.
Fluorite also has properties of Thermoluminescence. This means that when Fluorite is
heated it can glow. This process, however, is a one shot procedure, so one sample can
show it and never show it again.
Fluorite mining in the United States started
around the 1800’s, near Illinois and Kentucky. Most of
the large scale mining operations where done
underground at depths of 1500 feet (dnr.state.il.us).
Open pit mines replaced underground mines and
Illinois and Kentucky totaled about ninety percent of
the mining operation in the United States. Large scale
mining in Illinois ended in 1995 when the mining of
Fluorite no longer became profitable.
Rogerly Mine, Weardale, England: www.mineral-auctions.com
Extraction and Environmental Impacts:
“Although some industrial processes can make use of
fluorite directly, releasing elemental fluorine from the mineral fluorite
requires a fair amount of processing. Hydrofluoric acid (HF) an
important raw material for the chemical industry and the source of
elemental fluorine gas, is produced by the following reaction: Fluorite
(CaF2) + sulfuric acid (H2SO4) = 2 HF + CaSO4 (anhydrite) The
reaction is typically carried out in horizontal revolving kilns that are
heated externally. Finely ground fluorite and a slight excess of strong
sulfuric acid are mixed in a hopper and introduced at one end of the
kiln. A large collector pipe at the other end captures the HF and other
gases released by the reaction, and the solid anhydrite is extracted by
a screw drive. The hot gases the come out of the reactor consist of
about 95% HF, 4% air and 1% other impurities that include H2SO4,
SiF4, H2O, CO2 and SO2. Pure HF boils at 19 degrees Celsius and
this relatively high boiling point is used to purify the gaseous mixture
by distillation. Theoretically, 1.95 tons of pure CaF2 will yield one ton
of HF, but impurities in the fluorite ore and the sulfuric acid generally
require that greater tonnages of both be used in the reactors. To obtain
elemental fluorine, anhydrous hydrogen fluoride undergoes
electrolysis to release hydrogen and fluorine gas at the cathode and
anode, respectively”. (http://www.isgs.uiuc.edu/faq/ggfaqs/GGQ52.html).
About ninety percent of the Fluorite that the United
States uses is imported from Mexico, China and Brazil.
The Fluorite that was extracted from the United States
primarily came from Illinois, which became the state’s
mineral because of it’s economic values.
Fluorite is also used to extract the Fluorine to
produce Hydrofluoric acid (HF). HF is used in refining
mineral such as aluminum and uranium and is a
component of rocket fuel.
Mines that have been exhausted have been left as scars upon the
land. Exhausted mines leave large tailings piles of limestones and
fluorite that have been left by companies that have abandoned the
sites. The pits themselves are filled with water and become sinkholes.
There are no hazards in mining fluorite, nor have there been any large
consequences on the land, when mines are abandoned. While Fluorite
is non-toxic in rock form, Hydrofluoric Acid (HF) is the strongest
acid. Use caution when handling it. There is ongoing research on the
effects of Fluorite mining and water quality.
Regions where Fluorite is found:
Purple: Rosiclare, Ill. , Cave-In-Rock, Ill., Putnam County, Hardin County, Ill., Putnam
County, Ky., Musquiz, Coahuila, Mexico.
Clear: Clay Center, OH., Toledo, OH. Mipimi, Durango, Mexico, Wilberforce, Ontario,
Silverton District, Colorado.
Green: Madoc, Marmara, Huntingdon, Hastings County, Ottawa, Canada. Namibia.
Rogerly, Mine, England.
Pink: France, Switzerland
Blue: Yuogangxian, Hunan Province, China, Mexico.
.
Hill-Ledford Mines, Illinois. www.northstarminerals.com
http://www.isgs.uiuc.edu/servs/pubs/geobits-pub/geobit4/assets/geobit4fig.gif
Denton Mine, Illinois: www.northstarminerals.com
References:
http://mineral.galleries.com/minerals/halides/fluorite/fluorite.htm
Jamison Brizendine and Lauren
McCollough sift through a Tailings Pile in
Mahoning Mine, Illinios. Photo Coutesy of
Meg Streepey.
http://www.isgs.uiuc.edu/servs/pubs/geobits-pub/geobit4/geobit4.htm.
http://www.uwgb.edu/dutchs/PETROLGY/Fluorite%20Structure.HTM
http://www.minerals-n-more.com/Fluorite_Info.html http://en.wikipedia.org/wiki/Fluorspar http://www.mii.org/Minerals/photofluor.html
Left: Fluorite “Window”, Mahoning Mine, Illinois:
www.mineral-auctions.com
http://dnr.state.il.us/mines/education/indus2.htm
Right: Musquiz, Coahuila, Mexico : www.mineralauctions.com
http://geoinfo.nmt.edu/publications/memoirs/34/home.html
Far Right: Okarusu Mine, Otjiwarongo, Namibia:
www.mineral-auctions.com
http://www.isgs.uiuc.edu/faq/gg-faqs/GGQ52.html).
http://www.mineralminers.com/html/fluminfo.htm
http://www.museums.udel.edu/mineral/mineral_site/displaycollection/Halides/100125_D3631.html
Chesterman, Charles. National Audubon Society of Minerals, 1979, Chanticleer Press.
Johnson, Ole. Minerals of the World, 2004, Narayana Press, Denmark.