flourine minerals

Fluorine, F, is one of the more reactive non-metals and is quite abundant with a crustal abundance of around 950 ppm.
World production is currently about 6 million tonnes with China, Mexico, Mongolia and South Africa the major supplies.

rock and gem magazine issue 63

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Fluorine, F, is one of the more reactive non-metals and is quite abundant with a crustal abundance of around 950 ppm. World production is currently about 6 million tonnes with China, Mexico, Mongolia and South Africa the major supplies. Its industrial uses are numerous with smelting and refining of metals such as steels and. aluminium taking a high percentage. Hydrochloric acid, hydrogen fluoride and uranium hexafluoride are important uses of this element. Others include fluorocarbons, in the semiconductor industries, etching, in teflons and a wide host of other chemicals in many other sectors of commerce. The main fluorine-bearing mineral is fluoride and has been described in another article in this series on calcium minerals. Fluorine is present in numerous minerals and is present in most classes including halides, carbonates, silicates, arsenates, phosphates and borates etc.

Villiaumite, NaF, is cubic mineral that can form cubic crystals up to 15 cm in size. Massive and granular aggregates are more abundant. It is a lovely carmine-red, lavender-pink or light orange colour with a white streak and has a vitreous lustre. This mineral is transparent and fluorescent in dark red and yellow colours under both SW and LW UV light. It possesses a perfect cleavage and is brittle with a hardness of 2-2.5. Villiaumite is soluble in water. The specific gravity is 2.79. Colour, chemistry and mode of occurrence help in its identification. It is a mineral of nepheline syenites, pegmatites and in some lakebeds. The mineral is associated with aegirine, sodalite, nepheline, neptunite, lamprophyllite, pectolite, serandite, eudialyte, ussingite, chkalovite, various zeolites and other species. Large very desirable crystallised specimens have come from Mont Sainti-Hilaire, Quebec, Canada; and from various sites in the Kola Peninsula, Russia. Other less locations are in Greenland, Namibia, USA, Guinea, and Brazil.

Bastnasite-(La), (La,Ce)CO3F, is an appealing dark brown mineral that is translucent and is similar to bastnasite-(Ce). It occurs as fine-grained to massive aggregates. The mineral crys http://www.mindatconference.org/ tallises in the hexagonal system. Its hardness is 4-4.5. Other physical properties are currently unknown. X-rays and chemistry are required for characterisation. It occurs in ankerite carbonatites and some sandstones accompanied by fluocerite, cerianite-(Ce) and calcite. This rare species occurs at three locations in the USA and in generally isolated occurrences in Russia, Sweden, Greece, Czech Republic, Germany, Norway, Australia, India and South Africa.

Synchisite-(Ce), Ca(Ce,La)(CO3)2F, is an uncommon mineral of hydrothermal origin in granites and syenites and is frequently found with astrophyllite, catapleite, neptunite, epididymite, elpidite, cordyite, fluorite, rhodochrosite, aegirine, feldspars, ewaldite, calcite, ,barite and many others. It is monoclinic and form large crystals with an acute pyramidal to tabular habits. They can be striated with syntactic intergrowths and twinned. The mineral is yellow, brown to grey in colour with a vitreous to subadamantine lustre, and can be greasy. It is brittle and translucent with a subconchoidal to splintery fracture. The hardness is 4.5 and its specific gravity is 3.9. The above properties, chemistry and occurrence are helpful features.
Synchasite-(Ce), is noted from some 30 countries with Greenland producing some large specimens. Austria, Australia, Canada, China, France, Germany, Italy, Norway, Switzerland, Russia and the USA have several locations within their borders.

Fluoborite, Mg3(BO3)(F,OH)3, is found as acicular to prismatic crystals that are hexagonal in character with interesting pyramidal terminations. Fan-like or stellate forms also occur. It is transparent to translucent with a colourless to white colour. It has a good cleavage and hardness of about 3.5. Fluoborite fluoresces cream-yellow under SW ultra-violet light. The specific gravity is 2.9. Its listed properties, environment of formation and chemistry aid in its characterisation. It is
an uncommon mineral of hydrothermal skarns in B-Mg-rich rocks along with ludwigite, chondrodite, magnetite, calcite, mooreite, willemite, fluorite, hydrozincite, pyrochroite and rhodochrosite. A selection of locations are know for this species and includes those in Sweden, USA, Canada, Scotland, Italy, Australia, North Korea, South Africa, China, Russia.

Creedite, Ca3Al2(SO4)(OH)2F8.2H2O, is a very attractive mineral that occurs as prismatic, blade-like to acicular crystals with several forms. Radiating, drusy and granular aggregates are also found. It can be colourless, white to purple in colour with a vitreous lustre. This mineral possesses a perfect cleavage with a conchoidal fracture and is brittle. The hardness is 4 and is transparent to translucent.
Its specific gravity is 2.7. Physical, chemical properties and occurrence is helpful here as well as its known distribution. It is a rare mineral in fluorite-rich hydrothermal deposits associated with fluorite, barite and kaolinite. Good sites for creedite include the celebrated Wagon Wheel Gap location in Colorado, USA and the Potosi mine and related locations around Santa Eulalia, Mexico, and at Colquiri, La Paz, Bolivia. Also collected from other nations.

Tilasite, CaMg(AsO4)F, is an fascinating arsenate species with a varied crystal habit. Ranging from equant, elongated to flattened crystals with complex domatic forms. Contact twins also exist. Subparallel groups, granular and massive forms are found as well. It is translucent with a white, grey, violet-grey, rose-red, olive-green to apple green colour. Its streak is white and the lustre is resinous to vitreous in character. A cleavage and several parting are present, and it is piezoelectric. This mineral may fluoresce pale yellow, pale pinkish orange to dark red under SW UV light. Its hardness is 5 and the specific gravity is 3.7. Distinguishing features are its varied crystal habits, chemistry, associations and physical properties. Tilasite characteristically develops in metamorphosed Mn-As deposits accompanied by numerous species like durangite, diopside manganberzeliite , svabite, allactite, dixenite, hematite, willemite, calcite, spessartine, braunite, barite and quartz etc. Locations for this mineral are to be found in Sweden, Switzerland, Italy, Germany, Macedonia, Russia, India, Namibia, Algeria, Australia and the USA.

Fluellite, Al2(PO4)F2(OH).7H2O, can be found as transparent colourless, white to pale yellow orthorhombic crystals with a dipyramidal form, with some variation in habit. Aggregates and massive to powdery forms also occur. Physical properties include two indistinct cleavages, a low hardness of 3 and a specific gravity of 2.1. The mineral has a vitreous lustre and can fluoresce creamy white under LW UV light.
The listed properties, chemistry and mode of occurrence are helpful here. Fluellite is a rare secondary species, formed by the weathering of pre-existing phosphates in granitic pegmatites. Fluorapatite, wavellite, phosphosiderite, strengite, aldermanite, caxoxenite, variscite, turquoise, fluorite and quartz all can occur with it. Quite a variety of different places are now known for this species.
These include those sites in England, Germany, Czech Republic, Spain, Belgium, Italy, France, Sweden, USA, Argentina, Australia and Morocco.

Topaz, Al2SiO4(F,OH)2, is a very attractive mineral that forms varied orthorhombic crystals from short to long prismatic crystals with typically morphologically complex habits, making their study a great interest to collectors. Some crystals are etched on some faces from certain locations. Massive and granular forms are abundant. The colour range is very variable from colourless, through white, grey, yellow, brown, orange, blue, violet, green, pink and red of various shades. The lustre is vitreous to glassy with a white streak. It has a perfect cleavage with a subconchoidal to uneven fracture. A high hardness of 8 is present and is brittle.
Topaz is both pyroelectric and piezoelectric in character. The mineral is transparent to opaque with inclusions. Its specific gravity varies from 3.4-3.6. Diagnostic properties include its high hardness, perfect cleavage, occurrence and specific gravity. This species is found in a wide range of diverse geological environments and is very abundant. These include pegmatites, greisens, hydrothermal veins, volcanic rocks, rhyolites, granites, high-temperature metamorphic rocks, and also in detrital deposits. Euehedral crystals occur predominantly in pegmatites.

Commonly encountered associates are microcline, muscovite, zinnwaldite, tourmalines, columbite, quartz, cassiterite, beryl, hematite, rutile, scheelite, sphalerite, pseudobrookite, bixbyite, euclase, lepidolite series, ferberite-huenerite and chalcopyrite etc. Very large gems have been cut, i.e. over 22,000 carets and extraordinarily huge crystals weighing at about 32kg!
Specimens of such material are commonly available at the various Rock ’n’ Gem Shows across the country. A great endless list of localities are know with room here for just a few: Germany, Brazil, Pakistan, Namibia, Ukraine, Russia, Afghanistan, USA, Australia, Burma, Canada, China and Madagascar all producing outstanding specimens.

Norbergite, Mg3(SiO4)(F,OH)2, is a contact metamorphic mineral produced by impure carbonate sediments into which plutonic rocks and pegmatites have introduced fluorine, iron and boron-rich fluids.
Dolomite, calcite, tremolite, grossular, wollastonite, forsterite, monticellite, cuspidine, fluorborite, ludwigite, fluorite, phlogopite series, clinohumite and other typical skarn minerals accompany it.
Norbergite crystallises in the orthorhombic system with thick tabular crystals, typically with rounded highly modified faces.
Granular forms also are found. It can be tan, yellow, orange, brown, pink with a purplish tint and white with a vitreous to resinous lustre. This species is transparent to translucent in character and is brittle.
It possesses an uneven to subconchoidal fracture with a hardness value of 6-6.5. The specific gravity is 3.1 and may fluoresce canary-yellow under SW UV light. It is a member of the humite group and thus may be difficult to identify. Optical and x-rays tests are helpful methods. This mineral has been cut into small gems in the 1 to 3 carat range, but they tend to be quite dark. Classic occurrences are found in Sweden, Finland, Scotland, Switzerland, Italy, Russia, India, Pakistan, USA and Canada.

We will next discuses the minerals containing the very rare elements rubidium and gallium.
By John Betterton

 

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