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Fluorite

Chemical formula: CaF2
Density: 3.1÷3.3
Hardness: 4 (Mohs scale)
Crystallization: Cubic system

Origin and properties

Fluorite is frequently found in simple or geminate cubic or cubic-octahedral crystals; it is not rare in compact ore masses, sometimes coarsely crystalline.
When pure, it is colourless and perfectly transparent, but it can also be pale to dark blue, yellowish, green, pink, purple and even black (antozonite variety).
Fluorite is one of the most widespread minerals making up the gangue of hydrothermal metalliferous seams. It originates from high to medium thermal solutions.
It is an accessory mineral in the cavities of many intrusive, effusive and schisto-crystalline acid or intermediate rocks.
It can also have a sedimentary origin, probably due to deposition in confined basins from thermo-mineral rich waters of volcanic origin.

Ores

From the economic viewpoint, the most important fluorite ores are those from Germany from the Harz region, Bavaria, Thuringia and the Black Forest, and those from Derbyshire, in England.
Considerable ore bodies are also found in the Massif Central (France), in Russia and the United States.
In Italy the most exploited ores are those from the provinces of Brescia and Bergamo (Lombardy), where fluorite forms the gangue of sulphured minerals (blende and galena), and those from Corvara in Val Sarentina (South Tyrol) and Silius in Sardinia.
In the past, fluorite ores linked to the epithermal dikes of the Athesia Shelf, such as those from Prestavel (Trentino) and Vallarsa (South Tyrol), were intensely mined.

Utility

Fluorite is mainly used in the metallurgic industry for the production of easily meltable slags, the purification of silica-rich graphite, the manufacture of easily ground cement clinker, the preparation of some kinds of glass, hydrofluoric acid etc.
It is indispensable in the ceramic tile industry, in the optical industry, for the production of plastic materials and the metallurgic treatment of bauxite.
The purest and most transparent crystals are utilised for the construction of achromatic lenses and spectrograph prisms.

Production

The world production of fluorite is about 600,000 metric tons per year, out of which 55% are from Germany, followed by the United States and Great Britain.
In the 1960s and '70s, Italy produced nearly 100,000 metric tons/year of fluorite.
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