Fluorite

The name fluorite comes from the Latin fluere meaning to melt, flow. Certain fluoride minerals can lower the melting point of various ores, making them more fluid. The phosphorescence of fluorite was discovered by the mineralogist Mohs in the 19^th century.

Fluorite (formula CaF₂) has been used since the Middle Ages as an agent to liquefy the slag produced in metal smelting. In the 19^th century, cryolite (Na₃AlF₆) was used in the electrolytic preparation of aluminium, allowing a great expansion in the production of the metal.

Fluorite is the main ore of fluorine

The word fluorescence is derived from it. The emission of light by heated fluorite was discovered in the 17^th century.

This mineral, which occurs naturally in many places, has been given various names : Spatum vitreum or Calx fluorata amongst others, before it was given the name de fluorite. The commercial and industrial term is fluorspar.

Colours of fluorite

The earth's crust contains less than 0.1 % of fluorine. The colours are due to various elements in the crystal, such as yttrium and europium ions. The commonest are:

Fluorite verte (la Barre) Fluorite mauve
Green fluorite (from La Barre in France) and mauve, violet and dark violet fluorite (from Berbès). © Spathfluorminerals.com

Fluorite transparente Fluorite bleue
Transparent and blue fluorite (from Le Beix and Le Burg). © Spathfluorminerals.com

Fluorite jaune-doré
Yellow-gold fluorite. © Spathfluorminerals.com

After the ore has been concentrated for industry, there are two types of product:

" Acidic" or " chemical fluorspar containing more than 97 % of CaF₂. It is used by the chemical industry in the form of a powder;
" metallurgical "fluorspar containing less than 97 % of granular calcium fluoride (CaF₂).

In some cases, fluorspar is in competition with fluosilicic acid, a by-product of the phosphate fertilizer industry.

World production

Fluorite is used to make lenses that are transparent to ultraviolet light. It is used as a flux in metallurgy and is used in the manufacture of fluorine.

World production in 1996, 4,200,000 tonnes (figure from the Société française de chimie)

China: 2000
Mexico: 525
CIS: 300
Mongolia: 210
South Africa: 200
France: 130

In 1994, closure of the Buffalo Fluorspar Mine (South Africa), the largest mine in the world, which used to produce 180,000 t/year.

Main exporters: China, Mexico and South Africa. Main importers: United States (573,000 t in 1995) and Japan.

The ores in France contain about 50 % of CaF₂. The definitive end of production in France was in April 2006 (Tarn mines). France consumes around 100,000 t of acidic flurospar and around 20,000 t of metallurgical fluorspar.

Some of the French fluorite mines

Chaillac, Indre, operated by SIC until 2003.
Le Kaymar, Aveyron, operated since antiquity for silver and lead and since the 20^th century for fluorite.
Langeac, Haute Loire, one of the biggest producers, stopped in 1977.
Le Burg, Tarn, a very pure seam operated by a subsidiary of Péchiney.
La Pierre Perthuis, Yonne, the largest in tonnage and extent.

A sum total of around twenty production sites and nearly as many mineralogically interesting mines with fine specimens in some places.

Ponts de Pierre Perthuis, Yonne (site of an old fluorite mine). The smallest (oldest) dates back to 1770, and both lie on either side of La Cure. © DR

Fluorspar industry

Acidic flurospar and metallurgical fluorspar share equal tonnages of the world consumption of 3 million t/year. Fluorite is the source of the element fluorine for the chemical industry. It is used to make hydrogen fluoride (HF) :

CaF₂ + H₂SO₄———> CaSO₄ + 2 HF (300 °C, rotary furnace)
H₂SO₄ fuming concentrate.

The silica content of fluorite is limited as much as possible since it consumes the hydrofluoric acid, producing SiF₄ and H₂SiF₆. The gaseous hydrogen fluoride is purified to 99.9%. Over 2 tonnes of CaF₂ are required to obtain one tonne of hydrofluoric acid. CaSO₄, a by-product, can be used in the manufacture of plaster.

Uses of fluorite

Aluminium fluoride AlF₃ is produced (by dissolving alumina Al₂O₃) in molten cryolite (Na₃AlF₆) for the electrolysis cell to produce aluminium:
- cryolite: 83 %
- AlF₃: 7 %
- CaF₂: 5 %
- Al₂O₃: 5 %

20 to 60 kg of fluorspar are required per tonne of aluminium, representing 1/3 of the world consumption of fluorspar (Data from SFC). The aluminium industry is the largest emitter of atmospheric fluoride, with 75% of emissions. With the high temperature inside the cell during aluminiumproduction, some of the fluorides are released in gaseous form by evaporation of fluoride compounds, polluting the surrounding region unless efficient filters are installed.

The manufacture of fluorine derivatives: chlorofluorocarbons, hydrofluorocarbons, fluorinated polymers, simple fluorides, e.g. NaF for fluorinated table salt etc.
In addition, HF is the source of fluorine, by electrolysis, used to oxidise UF₄ to UF₆, for uranium enrichment by gaseous diffusion …
Fluorite is also used directly as a flux in the electrolytic production of aluminium and in the steel industry to fluidise the slag, with a consumption of 20 kg/t of steel produced, and as a flux for lime.
Fluorite is also used in the ceramics industry to opacify enamels. Fluorspar dosing must be precise, because the wrong dose can cause the enamel to boil. It is also used in the glass industry: opal glass, glass fibres, special glasses.