Articles

by Peter Rosewarne

Fluorite: cubic, common, cheap (comparatively, but can be costly), contains calcium, and colourful, are some of the "C" words that can be used to describe this mineral. While good specimens of fluorite from classic localities aren’t cheap, most are cheaper than good specimens of ‘higher-end’ minerals such as azurite, dioptase, tourmaline and beryl and it is possible to build up a good collection of fluorites from worldwide localities. You are also likely to get a nice-sized hand-specimen if you buy one, unlike with some of the previously named minerals. The name fluorite is derived from its easy fusibility and it is also the origin of the word fluoresce as it reacts under UV light. It has been used since Roman times for making ornaments, e.g. ‘Blue John’.

First, some technical stuff. Fluorite (CaF₂) is a halide and crystallises in the cubic class, usually as cubes or octahedra, and sometimes as massive deposits. It has a perfect octahedral cleavage and interpenetrating twinning is common. It has a hardness of 4 on Mohs’s scale and a white streak. It comes in a wide range of colours including green, purple, blue, yellow, amber, brown, pink and lavender, and all shades thereof, and also colourless and more rarely, red. Black fluorite is known as antozonite (did anyone know that? I didn’t). Colour zoning is common. These colours are apparently caused by rare earths such as yttrium or radiation. It is translucent to transparent. Fluorite is used as a flux in smelting, in the production of hydrofluoric acid and in optics. It occurs as a gangue mineral especially with lead and zinc sulfides in hydrothermal vein deposits, as replacement deposits and in pegmatites. It is also a relatively common accessory mineral in some igneous rocks but these occurrences are of no concern to the mineral specimen collector.

 Having got some of the basics out of the way, let’s look at some colourful and varied examples from famous and not so famous localities around the World, starting in Africa and including, from west to east, Europe, Asia - India, Russia, China, and the USA, all from the Rosey Collection, past and present, except for two, as indicated. Photograph credits (with permission) are given where I didn’t take them. We’ll start at home with Riemvasmaak and then work our way north before heading eastwards. I’ve also included some trivia that I found interesting, gleaned from the various references listed at the end.

Figure 1 Riemvasmaak

Africa

South Africa

Figure 1 above shows a fairly typical habit and association of fluorite from the Riemvasmaak site; green octahedra associated with white quartz. The best specimens have a glowing emerald green colour and most are originally covered in a thin layer of silica/quartz which must be removed with hydrofluoric acid, very carefully as this is a nasty acid, and good quartz crystals need to be protected from this process by a coating of wax. The deposit is located near the Orange River in pegmatites in the Namaqua-Natal Metamorphic Belt. Specimens first started emerging in numbers from 2006 and the best command high prices. The green colour is thought to be due to rare earth or radioactive species. 

Namibia

The Okorusu fluorite deposit is one of the largest in southern Africa and is located about 48 km north of Otjiwarongo in Namibia. Predominantly green, purple and more rarely yellow-coloured cubes are found in vugs in the otherwise massive deposit, which is of replacement origin associated with the Okorusu Alkaline Complex. Colour zoning is common and the yellow type often has dark edges, as shown in the example in Figure 2. Colour zoning in the green type is shown in Figure 3. Figure 4 shows a lustrous deep-green cubo-octahedral type with small white calcite crystals (photo by Fabre Minerals).

Figures 2, 3 and 4. All from Okorusu

 

Erongo, source of some beautiful fluorites, is glossed over a bit here because I sold the three good specimens that I had from this area and only kept one photograph, shown in Figure 5. However, the green colour just didn’t come out right. One particularly striking example from this area is the so-called “alien” or “eye” cubo-octahedral fluorites. These have unique green cores and almost black-looking octahedral faces giving a striking appearance, especially when backlit (see cover of Namibia 1 and p. 148/149). I shouldn’t have parted with my example!

Figure 5 

Madagascar

This country isn’t usually on people’s radar for fluorite specimens, being more commonly associated with e.g. liddicoatite tourmaline and andradite garnets. The specimen in Figure 6 (photo Fabre Minerals) comes from the Mandronaviro area, Toliara Province and is a deep green colour and shows dichroism in sunlight. This was a new source in 2018.

Figure 6

Morocco

Heading northwest to Morocco Figure 7 shows a nice yellow, cubic-habit fluorite from the Aouli Mine in Mibladen, Morocco. This is a lead-zinc vein-type deposit hosted in Palaeozoic-age rocks. An example of an unusual combination of yellow cubes with red quartz from the El Hammam (frequently miss-spelt as Hamman) Mine in Meknes Region is shown in Figure 8. This mine exploits veins in schists and limestone.

Figures 7 & 8

Europe

Spain

Hopping over the Mediterranean to Spain, next stop is the Berbes mining area, Asturias. This fluorspar deposit has been mined since the 1930s and is hosted in limestone and is famous for its blue-violet fluorite cubes. An example is shown in Figure 9. Associated minerals include quartz, calcite and barite. The nearby Moscona Mine also produces specimen-grade fluorite but usually of a yellow colour and often associated with white calcite crystals, as shown in Figure 10.

Figure 10 Calcite on fluorite

France-Switzerland

Check out the beautiful pink octahedral fluorites on smoky quartz being recovered in the French and Swiss Alps by intrepid Strahlers using advanced climbing techniques to access clefts in otherwise inaccessible faces. My example isn’t worth including here and this is one of the instances where a good pink fluorite will be very expensive. Two examples from Fabre Minerals are shown in Figures 11 and 12. Apparently, global warming is causing glaciers and other ice to shrink and thus opening up more areas for prospecting for such minerals.

Figure 11 from France

Figure 12 from Switzerland

England

Heading further north to England, the Rogerley Mine in Weardale, County Durham has produced some beautiful fluorite from specimen mining efforts since 1972, the first specimen mining operation ever undertaken in the UK. Since 2017 ownership and mining has been carried out by UK Mining Ventures Ltd (Crystal Classics) who expanded operations and discovered a large, richly mineralised cavity named the Diana Maria Mine. An example from the earlier mining is shown in Figure 13 (Rat Tail Pocket, 2009) and from the latter in Figure 14 (2017). These fluorites display a strong dichroism, changing from green to blue when rotated in natural light. I was browsing through the Denver Show report for 2018 in the 50 Years of What’s New in Minerals and my eye was caught by a specimen of Rogerley fluorite priced at $50 000, backing my “can be costly” comment in the opening line of this article. A gap here is the classic “Blue John” fluorite from Derbyshire, which has been mined since Roman times. I remember our downstairs neighbours giving me a couple of pieces of limestone with purple fluorite in the 1960s but I had no idea of their significance and they got lost along the way.  I also had no idea until reading Fluorite, The Collector’s Choice, that the name is derived from the French for blue and yellow, bleu and jaune. Elementary, I guess.

Figure 14 Rogerley mine specimen photographed indoors

Figure 14a the same specimen showing dichroism in sunlight

Germany

Next stop is to the east and the Erika Mine in Bavaria, Germany. The specimen shown in Figure 15 is an unusually deep amber colour. I couldn’t find much information about the mine and I bought the specimen because of its attractive colour. I was shocked to learn that John Veevaert of Trinity Minerals, from whom I bought this specimen, was killed in a car crash in the USA soon afterwards.

Figure 15

Asia

India Onwards to India and an unusual form of fluorite from the Nashik Quarry in Poona, shown in Figure 16. These are rounded ‘globules’ of yellow fluorite on quartz in Deccan ‘trap’ basalts, which are more famous for their stunning zeolites. The globules have a sort of ‘frosted’ surface. Red examples also occur here. Figure 16 Russia Next we continue on our eastward trajectory to Dal’negorsk (trns. most distant or remote mining town) in the Russian Far East, which is why I’ve included Russia under Asia. This is a famous polymetallic deposit producing collectable specimens of e.g. datolite, fluorite, ilvaite and pyrrhotite. This site, along with all other Russian sites, was unknown to Western collectors prior to 1988, after which the country opened up and local dealers were able to travel outside of Russia and international collectors and dealers were able to travel into Russia. There are eight mines in the Dal’negorsk area of which four were operating in 2001. The main ore body is a boron-rich skarn in a tectonically complex area because of its proximity to a subduction zone on the Pacific Rim. The example of water-clear cubes shown in Figure 17 is from the Second Sovetskiy Mine in Primorsky Kray (trns. Maritime Territory). These clear fluorites are sometimes referred to as “invisible fluorites” because of their perfect optical clarity. Figure 17 China As with Russia, mineral specimens and localities in China were largely unknown to Western collectors prior to the mid-1980s and as with Russia, there has since been a veritable explosion of specimens on the market with many World-class examples, including of scheelite, pyromorphite, ilvaite, fluorite, rhodochrosite, cassiterite and many others. The best fluorites come from the Shangbao and Xianghualing mines in Hunan Province and the Huanggang Mine in Inner Mongolia. The Shangbao pyrite mine, with the ore body hosted in a skarn, was exhausted of commercial quantities of pyrite by 1995 and attention was turned to mining of fluorite for the specimen market as it was not of industrial quality. Many thousands of beautiful fluorite specimens have been recovered and they are often of distinctive cubo-dodecahedron habit (see Figure 18) and an actual example in Figure 19. In some specimens the stepped faces are so numerous as to convert the cube to an almost spherical shape and these are termed “stepped cubic fluorite balls.” Figure 20 shows a specimen with a complex violet crystal of this habit on quartz and pyrite with calcite scalenohedrons (photo by Fabre Minerals). Figure 20. Shangbao Mine, China An example of the intense green and very transparent fluorite recovered from the Xiangghualing Mine is shown in Figure 21 (photo by Fabre Minerals). An unusual group of cubic fluorite crystals with edges bevelled by the rhombododecahedron (if you are bevelled by this term, Google it!) is shown in Figure 22 from the Huanggang Mine in Inner Mongolia. This is an unusual (unique?) habit for the species. The colour is very deep and vivid, between indigo and navy blue and this form is totally different from other Huanggang specimens. The fluorite is hosted in a Fe-Sn skarn deposit. United States of America We end this World tour in the USA, starting with one of the best and most prolific fluorite specimen localities ever discovered, in the Southern Illinois Fluorspar District. The deposits comprise of hydrothermal veins, with very few specimens obtained because of a lack of cavities for crystal growth, and bedding replacement, where most of the good specimens have been recovered. The latter was formed by rising mineralised solutions in limestone encountering an impermeable cap of shale. Over about 50 years up to the closure of the last mine in 1995, millions of specimens were recovered. Blue, purple, raspberry and yellow are the main colours of the mainly cubic aggregates, with zoning being common. Some specimens are coated with varying amounts of white calcite crystals. Some examples of the specimens obtained from the Denton, Minerva No. 1 and Annabel Lee mines near the town of Cave-in-Rock are shown in Figures 23 (photo by Fabre Minerals), 24, 25 and 26.    Moving to Tennessee we come to the famous Elmwood Mine which exploits a low temperature hydrothermal emplacement deposit with sphalerite being the main ore. Unique combos of sphalerite with fluorite, calcite and barite have been found here, rarely with all four minerals present. Three examples of fluorite on sphalerite are shown in Figures 27, 28 and 29, the latter with purple fluorite and off-white barite, that almost looks like a ball of mashed potato, sitting atop dark brown sphalerite. Fig. 29. Fluorite with barite and sphalerite, Elmwood Mine Our last stop in the USA is the White Rock Quarry, Clay Center, Ohio. This site was featured in the September–October 2020 issue of The Mineral Record. The quarry was opened in the 1870s and has been producing white lime and more recently rip-rap, aggregate and armour stone from dolomite. Cavities in the dolomite host fluorite, celestite, calcite and sphalerite. It is most famous for its prolific output of fine fluorite on celestite specimens. The fluorite from this locality is unique in its “root beer” brown cubes on blades of white celestite.  The brown colour of the fluorite is attributed to microscopic inclusions of hydrocarbons. An example is shown in Figure 30 (photo by The Mineral Gallery). Figure 30 Fluorite/celestite. Clay Centre, Ohio Where in the World? And finally, a mystery piece obtained from The Crystal Cave shop at the Waterfront many years ago. I don’t have any provenance for it but it is a pretty piece comprising small cubes of deep purple fluorite with a dusting of drusy quartz and what I think are very small dark lustrous crystals of sphalerite, on a matrix of grey quartzite – at least that’s my interpretation (Figure 31). Leafing through The Hoppel Collection of Fine Minerals Auction 1 catalogue, I came across a very similar, albeit bigger and better, example from the Cave-in-Rock area (Lot 87057 on p. 50) and am inclined to attribute my specimen to this source.   The final two “C” words for this article are concluding comment. I personally think these articles are more authentic if illustrated by one’s own specimens of whatever is being discussed, wherever possible. However, this usually limits the quality of the specimens and that is the case with this article. The reader is therefore encouraged to source some of the publications listed below, which many of you have no doubt already done, and gaze in wonder at the many superb world-class fluorite specimens illustrated therein, and dream on…   References Cairncross, B. (2004). Field Guide to the Rocks and Minerals of Southern Africa. Struik. Cape Town. Crystalline Treasures: The Mineral Heritage of China. Supplement to the Mineralogical Record, January-February 2013. Allen Press, Kansas. Deer, WA. Howie, RA. and Zussman, J. (1992). An Introduction to the Rock-Forming Minerals. Fisher, J. et al. Eds (2006). Fluorite The Collector’s Choice. Lithograpie LLC. Connecticut. Gloria A. Staebler and Wendell E. Wilson. Eds. (2008). American Mineral Treasures. Lithographie LLC. Connecticut. Heritage Auctions (2013). Nature and Science Auction: The Hoppel Collection of Fine Minerals. Auction 1. Dallas. Heritage Auctions (2014). Nature and Science Auction: Fine Minerals, Gems & Lapidary Art. Dallas. The Mineral Record, May-June 2018. Vol. 49, No.3. (article on the Okorusu Mine). Allen Press, Kansas. The Mineral Record, January-February 2001. Vol. 32, No. 1.  Dal’negorsk! Allen Press, Kansas. The Mineral Record, November-December 2011. Vol. 42, No.6. China III. Allen Press Kansas. The Mineral Record, September-October 2012. Vol. 43, No. 5. China IV. Allen Press, Kansas. The Mineral Record, September-October 2020. Vol. 51, No. 5. Clay Center! Allen Press, Kansas. The Mineralogical Record (2020). Fifty Years of What’s New in Minerals. The Mineralogical Record. Tucson. Vol II 2004-2019. Von Bezing, L. Bode, R. and Jahn, S. (2014). Namibia 1. Bode. Salzhemmendorf, Germany.