Fluorite

The fluorite ( fluorite in English, not to confuse with the term fluorite which in the same language means Fluor) is a known Minéral since antiquity. Its name comes from Latin fluere who wants to say melting, an allusion to its action like flux. Its usual name in industry is fluorite. It is composed of Fluorure of calcium, CaF2. It has a crystalline Structure Cubique; its habitus is often cubic, although the octahedral and dodecahedral crystals are not rare.

The color of this mineral is extremely variable: pure, it is colorless and transparent; but it can also be white, yellow, red, green, blue. Like all minerals containing of calcium, it colors the flame of a characteristic orange-red.

Chemical structure

The fluorite is an assembly of ions Ca2+ and F-. The F- anions are twice more numerous than the Ca2+ cations.

The structure of the fluorite corresponds to a filling of a structure host . The F- anions form a simple cubic lattice in which the Ca2+ cations occupy half of the cubic sites. The cations and the anions have about the same size. It is as possible to reverse the roles of the cations and the anions and to consider as the Ca2+ cations form a network host Cubique with centered faces and the F- anions occupy all the tetrahedral sites. These two visions are equivalent.

The structure of the fluorite can be comparable with two pennies networks : the Ca+ cations form under cubic lattice centered faces and the F- anions form under simple cubic lattice.

In the structure of the fluorite:
The Coordinence of the Ca2+ cations is of 8.
The Coordinence of the F- anions is of 4.

Layers

Discovered in 1529 with Sankt-Joachimsthal, Erzgebirge (Czech Republic).

One can find the fluorite in the form of seam, particularly with metal minerals like money and zinc, lead sulfides, where it forms part of the gangue. It can be then associated with Barytine, quartz and Calcite. One also finds it like deposit in the granites or of the metamorphic rocks like the gneiss.

The large layers are especially in China, with the Mexico, in South Africa, but the fluorite is distributed on all planet.

Uses

Apart from its decorative use, it is used as flux by the manufacturers of Acier, in manufacture of the Glass fiber and the Verre Opale and especially for the production of Acid hydrofluoric and derived fluorinated products, of which the Fluorure of aluminum, from which the Aluminum metal is obtained. The calcium fluoride is also used in instrumental optics, the properties of this glass being manifestly better than those of all other known glasses, in particular in term of transmission, refraction and chromatic dispersion.

The calcium fluoride ( CaF2 ) is obtained in the form of cubic Monocristal obtained under Vide by the method of Stockbarger. Its transmission is good Ultraviolet in the vacuum with the Infrarouge. Its excellent transmission of UV up to 170 Nm and its birefringent properties not makes of it an ideal material for the transmission of UV with short Wavelength. CaF2 for the infra-red is obtained at a definitely less cost starting from Fluorite extracted from natural mines. CaF2 being sensitive to the thermal shocks, it must be handled with precaution.

Gallery

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