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Mineral form of calcium fluoride / From Wikipedia, the free encyclopedia

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Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon.

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Deep green isolated fluorite crystal resembling a truncated octahedron, set upon a micaceous matrix, from Erongo Mountain, Erongo Region, Namibia (overall size: 50 mm × 27 mm, crystal size: 19 mm wide, 30 g)
CategoryHalide mineral
(repeating unit)
IMA symbolFlr[1]
Strunz classification3.AB.25
Crystal systemIsometric
Crystal classHexoctahedral (m3m)
H–M symbol: (4/m 3 2/m)
Space groupFm3m (No. 225)
Unit cella = 5.4626 Å; Z = 4
ColorColorless, although samples are often deeply colored owing to impurities; Purple, lilac, golden-yellow, green, blue, pink, champagne, brown.
Crystal habitWell-formed coarse sized crystals; also nodular, botryoidal, rarely columnar or fibrous; granular, massive
TwinningCommon on {111}, interpenetrant, flattened
CleavageOctahedral, perfect on {111}, parting on {011}
FractureSubconchoidal to uneven
Mohs scale hardness4 (defining mineral)
DiaphaneityTransparent to translucent
Specific gravity3.175–3.184; to 3.56 if high in rare-earth elements
Optical propertiesIsotropic; weak anomalous anisotropism; moderate relief
Refractive index1.433–1.448
Solubilityslightly water soluble and in hot hydrochloric acid
Other characteristicsMay be fluorescent, phosphorescent, thermoluminescent, and/or triboluminescent

The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 4 as fluorite.[6]

Pure fluorite is colourless and transparent, both in visible and ultraviolet light, but impurities usually make it a colorful mineral and the stone has ornamental and lapidary uses. Industrially, fluorite is used as a flux for smelting, and in the production of certain glasses and enamels. The purest grades of fluorite are a source of fluoride for hydrofluoric acid manufacture, which is the intermediate source of most fluorine-containing fine chemicals. Optically clear transparent fluorite lenses have low dispersion, so lenses made from it exhibit less chromatic aberration, making them valuable in microscopes and telescopes. Fluorite optics are also usable in the far-ultraviolet and mid-infrared ranges, where conventional glasses are too opaque for use.