Fluorite

fluorite

halite

cryolite

spinel

Images

Formula: CaF2
Fluoride

Varieties

Yttrofluorite is a variety of fluorite containing an appreciable amount of trivalent yttrium (Y) taking the place of divalent calcium (Ca) cations in the fluorite structure (Mindat)
Images of fluorescing yttrofluorite

Properties

Specific gravity: 3.18
Hardness: 4
Streak: White
Colour: Colourless, white, purple, green, blue, yellow, pink, red. Fluorite which is purple in daylight is coloured by the Frenkel defect, where an electron displaces a fluorine F- ion, during growth or when radiation displaces it from its usual position. A deep green daylight colour can be caused by the divalent samarium ion Sm2+ and yellow by gadolinium Gd3+. Radiation from included or nearby radioactive atoms releases atoms of calcium and fluorine from the fluorite, causing a very dark violet colour, and the rare and beautiful pink fluorite from Switzerland is coloured by impurities of yttrium oxide YO2 (AM 52.1003-1008). Some fluorites are light blue because they contain an yttrium Y3+ ion substituting for the calcium near a fluorine vacancy, which is populated by two electrons; this complex centre absorbs in the violet and the yellow-green and so gives a blue hue (G&G XXIV.11).
Solubility: Slightly soluble in hydrochloric acid; moderately soluble in sulphuric acid; slightly soluble in water
Melting point 1403°C, boiling point 2500°C.
Common impurities: Y,Ce,Si,Al,Fe,Mg,Eu,Sm,O,ORG,Cl,TR
Environments:

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

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. It also may be precipitated at hot springs (R&M 88-2:134).
In carbonatites it is associated with albite and pyrite (HOM).
When fluorite occurs as a cavity fill in carbonate rocks it is usually associated with calcite, dolomite, anhydrite, gypsum and sulphur.
In hornfels of contact metamorphic rocks fluorite is associated with calcite and spinel (AS).
In hydrothermal vein deposits, fluorite may be found with calcite, dolomite, baryte, galena, sphalerite and molybdenite.

Fluorite may be found in granite, quartzolite and dolostone.

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

Fluorescence

Fluorite is often, but not always, fluorescent, generally stronger under long wave than under short wave ultraviolet. Pure fluorite, however, is colourless and perfectly transparent, and does not fluoresce. The divalent europium ion Eu2+ is the most common activator, and causes intense blue fluorescence. Other activators include divalent samarium Sm2+ causing red fluorescence, trivalent samarium Sm3+, trivalent europium Eu3+, dysprosium Dy3+ causing yellow fluorescence, holmium Ho3+, erbium Er3+, terbium Tb3+ and neodymium Nd3+, all these are rare earth elements (FLM).

Localities

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, K-feldspar variety 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 Rock Candy Mine, Grand Forks, Greenwood Mining Division, British Columbia, Canada, quartz pseudomorphs after fluorite have been found (KL p251). The fluorite is generally pale greenish yellow and fluoresces bright blue (Mindat photos).

At the Marron Volcanics of the Olalla Area South-Central British Columbia, Canada, fluorite has been found occurring as clear, colorless octahedra to 1 mm, intimately associated with brewsterite at the Yellow Lake road cut, and at a road cut along Highway 3A, green fluorite crystals to 1.5 mm have been found in cavities in laumontite veins (R&M 96.6.521-522).

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 Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Quebec, Canada, rhodochrosite pseudomorphs after fluorite have been found (KL p162).

At the Shijiang Shan-Shalonggou mining area, Inner Mongolia, China, the mineral deposits occur predominantly in veins of hydrothermal origin in skarn. Fluorite occurs sparingly as octahedral crystals to 1 cm at Shijiangshan; they are frequently coated by a quartz crust. At Shalonggou, however, attractive and large, pale green, octahedral crystals to 5 cm on edge occur, also coated with a thin quartz crust (R&M 96.5.401).

At the Pili mine, Mexico, fluorite pseudomorphs after calcite have been found (KL p149).

At Trestia, south of Cavnic, Muramures, Romania, chalcedony pseudomorphs after fluorite have been found (KL p257).

At Dalnegorsk, Russia, quartz pseudomorphs after fluorite, and calcite pseudomorphs after fluorite, with a quartz coating, have been found (KL p252, 153).

At Wheal Mary Ann, Menheniot, Cornwall, England, UK, quartz pseudomorphs after fluorite have been found (R&M 95.3.275). The fluorite is generally pale greenish yellow and fluoresces blue (Mindat photos).

At the Whiteheaps Mine, Hunstanworth, Coounty Durham, England, UK, colourless to pale purple fluorite occurs associated with quartz, ankerite and calcite (R&M 95.4.335).

At the Burtree Pasture mine, Cowshill, Stanhope, County Durham, England, UK, purple fluorite occurs with quartz, iron carbonates and calcite (SY p158, R&M 95.4.318)

At the Greenlaws Mine, Daddry Shield, Stanhope, County Durham, England, UK, well formed purple and amber coloured fluorite crystals are found, that fluoresce bright blue (R&M 95.4.320).

At the Eastgate Quarry, Eastgate, Stanhope, County Durham, England, UK, green fluorite occurs with internal purple colour zones. Yellow and purple fluorite is also found rarely (R&M 95.4.322).

At the Blackdene Mine, Ireshopeburn, Stanhope, County Durham, England, UK, purple fluorite occurs with galena and other sulphides on a quartz matrix. Yellow and green crystals of fluorite have also been found (R&M 95.4.317).

At the Rogerley Mine, Rogerley Quarry, Stanhope, County Durham, England, UK, green, purple and yellow fluorite has been found, often associated with galena. The best known are the colour-change crystals which show strong blue highlights in daylight, and are pure green in artificial light (R&M 95.4.327). These Weardale fluorites contain ten times more rare earth elements than do the non-fluorescent Derbyshire fluorites. The green colour is thought to be due to the presence of samarium Sm2+ as an impurity (https://e-rocks.com/blogs/11437/daylight-fluorescence-weardale-green-fluorspar).

At the Boltsburn Mine, Rookhope, Stanhope, County Durham, England, UK, fluorite is associated with siderite and calcite. Epimorphs of siderite after fluorite have been found here (SY p150, 158). Deep blue fluorite crystals occur associated with quartz, calcite siderite and galena (R&M 95.4.332).

At Frazer's Hush Mine, Rookhope, Stanhope, County Durham, England, UK, purple fluorite occurs with quartz, galena and sphalerite (R&M 95.4.334).

At the Redburn Mine, Rookhope, Stanhope, County Durham, England, UK, pale to medium green fluorite occurs with calcite, quartz and minor sulphides. Groups of small purple fluorite have also been found (R&M 95.4.332).

At the Stotfield Burn Mine, Rookhope, Stanhope, Co. Durham, England, UK, some purple and purple-green fluorite has been found associated with galena on a quartz matrix (R&M 95.4.329).

At the Heights Mine, Westgate, Stanhope, County Durham, England, UK, magnificent emerald-green fluorite crystals to 8 cm have been found, and also pale purple to colourless fluorite. Associated minerals include galena, calcite and aragonite (R&M 95.4.322).

At the West Pasture Mine, Stanhope, County Durham, England, UK, fluorite occurs which is apple-green when recovered, but which fades to purplish grey on exposure to sunlight (R&M 95.4.325).

At the Middlehope Burn, Westgate, Weardale, North Pennines, County Durham, England, UK, emerald-green fluorite occurs on a buff coloured friable matrix (R&M 95.4.322).

At Rotherhope Fell Mine, Black Burn Area, Alston Moor, Eden, Cumbria, England, UK, fluorite occurs with calcite and quartz on massive black limestone (SY p155). Purple is the most common colour for the fluorite, and some crystals have a surface layer of amber yellow surrounding a purple core (R&M 95.4.330).

At the Brownley Hill Mine, Nenthead, Alston Moor, Eden, Cumbria, England, UK, good quality specimens of amber coloured fluorite are found (R&M 95.4.337).

At the Rampgill Mine, Nenthead, Alston Moor, Eden, Cumbria, England, UK, some specimens of small, pale yellow fluorite crystals with siderite on quartz have been found (R&M 95.4.337).

The Hilton Mine, Scordale, Murton, Eden, Cumbria, England, UK, is famous for yellow to amber coloured fluorite, and is one of the few localities in the region where fluorite is found together with barium minerals, such as baryte (R&M 95.4.340).

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 Croft Quarry, Croft, Blaby, Leicestershire, England, UK, three generations of colourless to pale yellow or pale greenish blue fluorite occur, associated with chalcopyrite, analcime and calcite. No specimens have been seen where any of the three generations of fluorite have been enclosed by later minerals, indicating that the fluorite crystallisation is very late in the paragenesis (JRS 20.15-16).

At the Elbolton Mine, Elbolton Hill, Thorpe, Craven, North Yorkshire, England, UK, colourless fluorite has been found with a deep indigo-blue surface layer (R&M 95.4.343).

At the Coldstones Quarry, Greenhow, High and Low Bishopside, Harrogate, North Yorkshire, England, UK, colourless to pale yellow fluorite crystals are found, many with a thin blue or purple layer at the surface (R&M 95.4.343).

At the Gillheads Mine, Skyreholme, High and Low Bishopside, Harrogate, North Yorkshire, England, UK, fluorite is typically colourless to pale yellow with a characteristic thin blue/purple layer at the surface (R&M 95.4.343).

At the Raygill Level, Hawes, Wensleydale, North Pennines, North Yorkshire, England, UK, colourless, pale yellow and purple fluorite is associated with baryte and sulphides (R&M 95.4.342).

At the Seata Mine, Aysgarth, Richmondshire, North Yorkshire, England, UK, yellow and amber coloured fluorite occurs with galena (R&M 95.4.342).

At the Wet Grooves Mine, Carperby-cum-Thoresby, Richmondshire, North Yorkshire, England, UK, colourless to yellow fluorite occurs with baryte and calcite (R&M 95.4.342).

At the Allenheads Mine (Beaumont Mine), Allendale, Northumberland, England, UK, pale lavender crystals of fluorite associated with sphalerite and siderite, and purple fluorite associated with siderite and galena have been found (R&M 95.4.336).

At St Peter's Mine, Sparty Lea, Allendale, Northumberland, England, UK, good quality green fluorite has been found, and also amber and purplish-grey crystals associated with galena, often with overgrowths of siderite or quartz (SY p155, R&M 95.4.337).

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

At the East Arn Gill mine, Muker, Richmondshire, North Yorkshire, England, UK, fluorite has been found with included zones of tiny chalcopyrite crystals with cerussite coated galena crystals (SY p150).

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 Duck Street Quarry, Greenhow, High and Low Bishopside, Harrogate, North Yorkshire, England, UK, fluorite is found with inclusions of chalcopyrite (SY p158).

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 opal variety hyalite (R&M 93.5.409).

At the Potter-Cramer mine, Vulture Mining District, Maricopa county, Arizona, USA, fluorite is quite common as octahedral crystals that are milky white, pale blue or dark purple-brown. The milky white and blue fluorite fluoresces under LW, MW and SW UV, being strongest under LW, and typically europium-activated violet in colour. The darker-coloured fluorite does not seem to fluoresce (R&M 96.1.29).

At the Galena King Mine, Coyote Canyon, Tijeras Canyon Mining District, Bernalillo county, New Mexico, USA, the deposit is hosted in granite gneiss. Fluorite ranges in colour from a deep ultramarine-blue to a medium blue, and some pockets produced teal blue–green crystals. The blue fluorite changes colour, blue under daylight and purple under incandescent light. Crystals to 4 cm typically form as intergrown groups on plates to 45 cm. Most crystals are cubes, but a few pockets have produced stepped octahedra. The majority of pockets experienced a secondary growth of opaque reddish-brown drusy fluorite covering the internal blue colour of the primary fluorite. Some of the fluorite is associated with slightly altered galena and bladed baryte groups (R&M 95.5.406).

At the Highland Mary (Frustration) Mine, Tijeras Canyon District, Bernalillo county, New Mexico, USA, fluorite veins are hosted in granite. Fluorite occurs as sea-foam green stepped octahedra or blue stepped cubes; simple cubes are uncommon. Crystals are usually smaller than 2.5 cm, but some reach 5 cm on edge. The fluorite may exhibit a colour change, appearing bluish in artificial light and more of a green colour in sunlight (R&M 95.5.407).

At the Lucky Bill (Octoroon) Mine, Tijeras Canyon District, Bernalillo county, New Mexico, USA, fluorite occurs as typical stepped blue cubes partially covered with groups of white baryte blades. The mine has also produced large plates of baryte crystals (R&M 95.5.407-408).

In the Bluewater Area, Zuni Mountains, Cibola county, New Mexico, USA, fluorite forms as layered vein fillings, and when split open, plates of teal blue–green botryoids with adamantine luster (unusual for fluorite) are revealed (R&M 95.5.409).

In the Zuni Mountains, Cibola county, New Mexico, USA, fluorite occurs in veins in granite and gneiss at the Prospector’s, Bonnekay, Porter-Mirabal, Grants and Bonita mines. There is much variety in colour with many shades of blue, purple, green, yellow, and brown. Most crystals are simple cubes or stepped cubes to 5 cm, but some specimens from the Bonnekay mine show stepped purple and green octahedra to 2.5 cm (R&M 95.5.408-409).

At the Stevenson-Bennett Mine, Organ Mining District, Organ Mountains, Doña Ana county, New Mexico, USA, the deposit is much more famous for fine wulfenite but one pocket of fluorite was discovered near the water level, that produced lustrous, transparent purple and green modified cubes that are most likely spinel twins, the only recorded occurrence of this habit in the state (R&M 95.5.410).

The Ruby (Hayner) Mine, Modoc District, Doña Ana county, New Mexico, USA, consists of veins and minor replacement bodies in limestone. Some cubic white and colourless fluorite crystals to over 2.5 cm on gossan matrix have been collected here (R&M 95.5.410).

At Palm Park Mine, Palm Park, Rincon Mining District, Doña Ana county, New Mexico, USA, yellow to amber-colored cubic fluorite to 5 cm is sometimes associated with the primary ore minerals (R&M 95.5.410).

At the Tortugas Mine, Tortugas Mountain District, Doña Ana county, New Mexico, USA, veins are hosted in limestone. Crystals are generally cubes modified by the dodecahedron and range in colour from green to purple to blue, and up to 5 cm across (R&M 95.5.410).

At Doublestrike Prospects, Bound Ranch District, Grant county, New Mexico, USA, teal blue–green cubes of fluorite modified by white or dark purple dodecahedral edges have been found (R&M 95.5.411).

At Little Rock Mine, Deadman Canyon-California Gulch-Whitewater Canyon Area, Burro Mountains District, Grant county, New Mexico, USA, veins of copper mineralisation and minor fluorite are hosted in a monzonite porphyry that is associated with the nearby copper porphyry deposit. Plates of dark purple octahedral fluorite crystals occur on a white matrix, some plates having a second generation of tiny pale purple crystals preferentially coating faces of the larger octahedra (R&M 95.5.412).

At the Lucky Irishman claim, Southwest and Central Burro Mts Area, Burro Mountains District, Grant county, New Mexico, USA, opaque blue-green botryoidal fluorite on
quartz has been found (R&M 95.5.412).

At the Pine Canyon deposit, West Burro Mountains, Burro Mountains Mining District, Grant county, New Mexico, USA, fluorite occurs commonly as octahedral crystals to approximately 5 cm, typically medium to dark purple with green cores, although a few specimens show the inverse. Occasionally, the purple crystals have a colourless or pale green rind. The most distinctive characteristic is that the crystal faces are convex. Plates of crystals are common, with many consisting of purple octahedra on a white quartz matrix. Nearly all specimens coming out of the ground are coated with a 1–2-mm thick layer of quartz (R&M 95.5.412-413).

At the Tyrone Mine, Tyrone Area, Burro Mountains Mining District, Grant county, New Mexico, USA, medium green octahedral crystals of fluorite to 3.2 cm, some on a white quartz matrix, have been found in a vein of fluorite in the main pit. The pit has also produced banded carving-grade fluorite with green, purple, and white zonation (R&M 95.5.414).

At the Gila Fluorspar Mining District, Grant county, New Mexico, USA, many fine specimens of green and purple octahedral fluorite have been found in vein systems hosted in volcanic rocks (R&M 95.5.414).

At the Foster Mine, Gila Fluorspar District, Grant county, New Mexico, USA, fluorite occurs as plates of green octahedra to 10 cm, solid purple octahedra, two-toned green and purple octahedra, and blue and green octahedra. Some crystals have been covered by a later-stage quartz. Octahedra can be modified by the cube or can often exhibit a late-stage growth of cubes (R&M 95.5.414-415).

At the Last Chance Mine, Gila Fluorspar Mining District, Grant county, New Mexico, USA, fluorite occurs as green octahedra to 7 cm, often with a late-stage growth of white fluorite (R&M 95.5.415).

At The Cleft, Gila Fluorspar Mining District, Grant county, New Mexico, USA, an outcropping vein of fluorite near the Last Chance mine has produced large plates of medium-to-dark green fluorite octahedra to 10 cm on a side, showing the typical stepped octahedral form (R&M 95.5.415).

At the Turkey Creek Area, Gila Fluorspar Mining District, Grant county, New Mexico, USA, large, 20-cm, plates of purple stepped fluorite octahedra to 2.5 cm have been found, and both green and purple octahedra with crystals to 3 cm (R&M 95.5.415).

At the Watson Mountain Prospect, Gila Fluorspar Mining District, Grant county, New Mexico, USA, fluorite occurs as green and purple octahedra to 8 cm. Some of the green crystals are stepped, and all have a tendency to a late-stage growth of white fluorite (R&M 95.5.415-416).

At the Bluebird Prospects, Gold Hill District, Grant county, New Mexico, USA, fluorite is hosted in veins cutting granite. Green and purple crystals to 5 cm with cubic, octahedral, and dodecahedral faces have been found, and also, in one small pocket, stepped octahedral fluorite crystals modified by the hexoctahedron (R&M 95.5.416).

At Black Mountain (Polyanna Group), Hidalgo county, New Mexico, USA, fluorite has been found as translucent to transparent, honey-brown to chocolate-brown and black-brown cubes to 3 cm, with hexoctahedral modifications (R&M 95.5.416-417).

At the Gallinas Mountains, Red Cloud District, Lincoln county, New Mexico, USA, fluorite occurs in breccia zones in sediments and a porphyritic trachyte associated with fault zones. Small crystals of deep purple, stepped cubic fluorite with dodecahedral modifications colored red by hematite have been found. Bastnäsite is also present (R&M 95.5.417).

At the Smokey Bear Quartz Claims, Lincoln county, New Mexico, USA, fluorite is a minor constituent; some fluorite octahedra have been found in association with the smoky quartz for which the area is famous. The fluorite forms as medium green octahedra sometimes with purple cores, exceptionally to 5 cm, or as white colloform aggregates to 2 cm growing on the sides of quartz crystals (R&M 95.5.417-418).

At Cookes Peak Mining District, Luna county, New Mexico, USA, the deposits are small carbonate replacement deposits in limestone. Fluorite is one of the primary gangue minerals and occurs as green and purple octahedra (R&M 95.5.418-419).

At Lucky Mine, Fluorite Ridge District, Luna county, New Mexico, USA, most of the deposits are fluorite fissure veins hosted in monzonite, basalt, and young extrusive rocks, and there are a couple of small replacement bodies in limestone. Fluorite from the vein systems is typically cubic; fluorite from the replacement deposits consists of highly modified cubes and octahedra. Crystals are typically no larger than 6 cm, but some reach 12 cm. Colours include many shades of purple, green, blue, white, and rarely red. Some of the crystals rest on tiny white quartz crystals (R&M 95.5.419-420).

At Small Fry prospect, El Rito, El Rito District, Rio Arriba county, New Mexico, USA, rounded crystal aggregates of fluorite are found in veins in igneous rock and may be associated with small white baryte crystals and calcite. Individual botryoids are generally no more than 5 cm across and often form colloform groups. The fluorite is usually medium to dark purple and sometimes is coated with iridescent iron oxide (R&M 95.5.420).

At El Cuervo Butte, Santa Fe county, New Mexico, USA, transparent colorless cubes of fluorite have been found associated with baryte and minor galena. The cubes reach 2.5 cm and are modified by the dodecahedron (R&M 95.5.420).

At the San Pedro Mine, New Placers District, Santa Fe county, New Mexico, USA, fluorite is rare, but it has been found in the skarn system both as deep purple octahedra to 1.5 cm associated with hematite and laumontite, and as small grass-green modified cubes (R&M 95.5.420).

At the Bohrnstedt Prospect, San Andres Mountains, Sierra county, New Mexico, USA, a military area, purple-black cubes of fluorite were abundant on the dumps. The crystals, which had been exposed to the sun for more than sixty years, were not much paler in colour than material found underground. This is one of the very few areas in the state where fluorite is not very photosensitive. Single cubes reach 7.5 cm and typically grow as groups on plates of small quartz crystals (R&M 95.5.421).

At the Parker Prospect, Caballo Mountain District, Sierra county, New Mexico, USA, the deposit is hosted in limestone. Fluorite occurs as green cubic and octahedral crystals to 3.5 cm, some of them coated with a layer layer of crystalline quartz (R&M 95.5.421-422).

At the Black Knife group (Prospectors Delight Mine), Cuchillo Negro District, Sierra Cuchillo, Sierra county, New Mexico, USA, small, white to pale green fluorite crystals to 2 cm dot iron oxide–stained quartz pseudomorphs after scalenohedral calcite (R&M 95.5.422).

At the Fairview Mine, Cuchillo Negro District, Sierra Cuchillo, Sierra county, New Mexico, USA, green botryoidal fluorite occurs covered with large epimorphs of quartz after rhombohedral calcite (R&M 95.5.422).

At the Vindicator Mine, Cuchillo Negro District, Sierra Cuchillo, Sierra county, New Mexico, USA, the deposit is a copper-lead-zinc garnet skarn system hosted in limestone adjacent to a contact with a monzonite sill. Fluorite has been found as mint-green octahedra to 2.5 cm on white quartz, and as green octahedra to 2.5 cm coated by a thin layer of snow-white albite associated with drusy quartz and microcrystals of green mottramite (R&M 95.5.423).

At the Lorraine prospects, Derry District, Sierra county, New Mexico, USA, the deposit is hosted in limestone. Fluorite has been found as stepped purple and green octahedra to 15 cm, with a later generation of purple-blue fluorite overgrowing select faces of the octahedra. It has also been found as complex teal blue–green cubes to 4 cm, some associated with brownish-yellow baryte and as transparent, pale green cubes modified by the dodecahedron (R&M 95.5.423-424).

At the Nakaye Mine, Derry District, Sierra county, New Mexico, USA, limestone beds have been replaced by fluorite. Associated minerals are colourless to white calcite crystals to 10 cm and small grey-green baryte crystals to 1 cm. Fluorite from the Nakaye mine is always cubic and can reach sizes of approximately 15 cm. Most crystals are in the 1–7-cm size range. Colour is varied, ranging from shades of blue, purple, green, grey, white, brown, and, in rare cases, yellow. The blues and purples tend to be very photosensitive; specimens placed in direct sunlight can fade to grey within 20–30 minutes. Penetration spinel twins are relatively common (R&M 95.5.424-425).

At the Lemitar Mountain District, Socorro county, New Mexico, USA, fluorite occurs as gemmy pale green cubes to 4 cm on matrix, collected from small fluorite veins in granite (R&M 95.5.425).

At the Blanchard mine, Hansonburg District, Socorro county, New Mexico, USA, fluorite occurs as “Blanchard Blue”, medium to dark blue cubes to about 2.5 cm scattered and perched on white quartz, also as teal-blue and green cubes to 5.4 cm in quartz matrix. Exceptional blue and purple cubic fluorite to 12 cm showed zoning of saturated purple cores with a blue rind. The Blanchard mine also produced one of the handful of known penetration twinned fluorite specimens (R&M 95.5.425-427).

At the Linchburg Mine, Magdalena District, Socorro county, New Mexico, USA, there are both carbonate replacement deposits and skarn deposits where limestone beds have been replaced adjacent to a rhyolite sill and are also associated with a monzonite stock. Fluorite occurs as gemmy, highly etched pale purple dodecahedral crystals atop a first generation of pale green octahedra, and also as of etched mint-green octahedra associated with white baryte (R&M 95.5.427).

At Cabresto Creek, Questa District, Taos County, New Mexico, USA, this deposit is a small series of hydrothermal veins with fluorite and quartz. The fluorite occurs as dark purple crystals with green cores to 2.5 cm, typically showing multiple-growth octahedra, on a white crystalline quartz matrix (R&M 95.5.427-428).

Amity, Town of Warwick, Orange county, New York, USA, is an area of granite intrusions into marble and associated gneiss. The marble is mostly composed of white crystalline calcite that often has small flakes or spheres of graphite and phlogopite. Fluorite occurs as small, deep purple crystals of roughly cubic habit, both in white marble and in serpentine. Fluorite is also found embedded in tabular phlogopite crystals (R&M 96.5.437).

At the Suever Stone Company quarry, Delphos, Van Wert county, Ohio, USA, fluorite occurs as small, cubic, bicolored yellow and purple crystals, rarely reaching 5 cm on edge. It is found occasionally in calcite-filled pockets lined with light brown fluorite that is fluorescent. The main concentrations of fluorite, however, are found as generally brown cubic crystals, either clear or translucent, in petroleum-containing pockets along with calcite, dolomite and/or pyrite. Rarely pockets contain fluorite needles, sheaves, and botryoids. The original needles are frequently covered with small cubes of fluorite of a later generation. Petroleum is present in all these pockets, and it is thought to be responsible for the brown colour of the fluorite. The surface layer of the sheaves and botryoids fluoresces to some degree, but the cores and needles show minimal fluorescence. The Suever fluorites differ from all other Ohio fluorites in that narrow dodecahedral faces {110} commonly occur, bevelling the edges between faces of the cube. Fluorite crystals here often contain phantoms with various depths of the usual brown colour (R&M 95.6.505-509, 512-514).

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).

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