Fluorite

halite

limestone

Formula: CaF2
Fluoride
Specific gravity: 3.18
Hardness: 4
Streak: White
Colour: Colourless, white, purple, green, blue, yellow, pink, red
Solubility: Slightly soluble in hydrochloric acid; moderately soluble in sulphuric acid; slightly soluble in water
Melting point 1403°C, boiling point 2500°C.
Environments:

Plutonic igneous environments
Pegmatites
Carbonatites
Sedimentary environments
Hot spring deposits
Hydrothermal environments

Fluorite is a common and widely distributed mineral; it mainly occurs as a pore-filling mineral in limestone and dolostone, and in mesothermal (moderate temperature) and hypothermal (high temperature) hydrothermal vein deposits associated with lead and silver ores. Less often it may be found as a primary mineral in igneous rocks and pegmatites, where it is a late-stage mineral following deposition of beryl, topaz and tourmaline (R&M 88-2:134). In carbonatites it is associated with albite and pyrite. It also may be precipitated at hot springs (HOM).

Fluorite may be found in granite, quartzolite and dolostone.

When fluorite occurs as a cavity fill in carbonate rocks it is usually associated with calcite, dolomite, anhydrite, gypsum and sulphur.
In hydrothermal vein deposits, fluorite may be found with calcite, dolomite, baryte, galena, sphalerite and molybdenite.

Pseudomorphs of quartz after fluorite are common. Fluorite also forms pseudomorphs after calcite, baryte and galena (Dana).

At Rumsby's mine, New South Wales, Australia, indications are that fluorite was formed at temperatures between 451 and 462oC in intersecting vein systems in granite. The paragenetic sequence included early stage smoky quartz, arsenopyrite, ferberite, bismuth, monazite, fluorite, beryl, ilmenite, adularia, muscovite and tourmaline group minerals. A later stage precipitated quartz, muscovite, chalcopyrite, pyrite and chlorite group minerals. Secondary alteration replacement minerals included scheelite after ferberite, chalcopyrite, pyrrhotite and cubanite, hematite and rutile after ilmenite and covellite after chalcopyrite. ( AJM 18.2.26 )

At the Ontario Gem Mine, Thunder Bay District, Ontario, Canada, a specimen with fluorite crystals on quartz variety amethyst has been found (R&M 94.4.338).

At Ashover, Derbyshire, England, UK, fluorite is associated with galena and sphalerite, and sometimes has inclusions of pyrite (RES p102, 103).

At the Odin mine, Castleton, Derbyshire, England, UK, fluorite is associated with baryte (RES p129).

At Treak Cliff, Castleton, Derbyshire, England, UK, fluorite is associated with calcite on a limestone matrix (RES p126).

At the Crich quarry, Crich, Derbyshire, England, UK, fluorite has been found with baryte and calcite (RES p100).

At Eyam, Derbyshire, England, UK, fluorite is associated with calcite, sphalerite and galena (RES p117).

At Hopping Pipe mine, Matlock, Derbyshire, England, UK, fluorite is often associated with minor galena or pyromorphite (RES p72).

At the Mill Close mine, Darley Dale, Matlock, Derbyshire, England, UK, fluorite occurs with galena and sphalerite, with minor pyrite and baryte, on a limestone matrix. Fluorite also has been found associated with hemimorphite (RES p92, 94).

At the Hampstead Farm quarry, Chipping Sodbury, South Gloucestershire, England, UK, fluorite has been found on a calcite matrix (RES p174).

At the Tockington limestone quarry, near Olveston, South Gloucestershire, England, UK, fluorite has been found on calcite in limestone (RES p170).

At the Croft quarry, Croft, Leicestershire, fluorite has been found associated with calcite, analcime and chalcopyrite (RES p189).

At the Rorrington mine, Chirbury, Shelve, Shropshire, England, UK, fluorite has been found with baryte (RES p287).

At Zacatecas, Mexico, fluorite occurs as groups of cubic crystals aligned along tubular voids in massive hyalite (R&M 93.5.409).

At the Findlay Arch Mineral District spanning parts of Ohio, Michigan and Indiana, USA, fluorite occurs together with calcite and celestine in Silurian and Devonian limestone. These minerals formed in cavities after the rock was laid down. The dark brown fluorite from this locality is coloured by inclusions of bituminous particulates, and fluoresces blue under shortwave radiation (R&M 93.2.110-133).

Alteration

aegirine, anorthite and F2 to albite, fluorite, magnetite and O2
6NaFe3+Si2O6 + 3CaAl2Si2O8 + 3F2 = 6NaAlSi3O8 + 3CaF2 + 2Fe2+Fe3+2O4 + 2O2
(AM55.126-134)

aegirine, anorthite, quartz and cryolite to albite, fluorite, magnetite and O2
12NaFe3+Si2O6 + 9CaAl2Si2O8 + 21SiO2 + 3Na2NaAlF6 = 21NaAlSi3O8 + 9CaF2 + 4Fe2+Fe3+2O4 + O2
It is only in anorthite-poor siliceous rocks that cryolite will form in preference to fluorite.
(AM55.126-134)

villiaumite, quartz and anorthite to albite and fluorite
2NaF + 4SiO2 + CaAl2Si2O8 = 2NaAlSi3O8 + CaF2
Villiaumite and quartz cannot co-exist because they combine with anorthite present in the assemblage to form albite and fluorite, according to the above equation (AM55.126-134).

Common impurities in fluorite: Y,Ce,Si,Al,Fe,Mg,Eu,Sm,O,ORG,Cl,TR

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