Tourmaline group

©

Click here to view Best Minerals and here for Tourmaline group minerals, here for Chromium-dravite, here for Darellhenryite, here for Chromo-alumino-povondraite, here for Dravite, here for Elbaite, Afghanistan to Nigeria, here for Elbaite, Pakistan to Zambia here for Feruvite, here for Fluor Buergerite here for Fluor-dravite, here for Fluor-elbaite, here for Fluor-feruvite, here for Fluor-liddicoatite, here for Fluor-schorl, here for Foitite, here for Liddicoatite, here for Luinaite-(OH), here for Magnesiofoitite, here for Olenite, here for Oxy-dravite, here for Oxy-rossmanite, here for Oxy-schorl, here for Povondraite, here for Rossmanite, here for Schorl, here for Tsilaisite and here for Vanadium-dravite. Click here for Best Minerals T and here for Best Minerals A to Z and here for Fast Navigation of completed Best Minerals articles.

Can you help make this a better article? What good localities have we missed? Can you supply pictures of better specimens than those we show here? Can you give us more and better information about the specimens from these localities? Can you supply better geological or historical information on these localities?



Tourmaline Group
Tourmaline is perhaps the main repository for boron in the earth's crust. Its stability field ranges from nearly standard temperature pressure condition (the weather outside) to 800 C and 60 kbar. It has a complex structure where many elements can enter into its composition and because of this the study of these elements and their location in the structure of the tourmaline species they can open a window on the conditions under which the tourmaline was formed and rocks that contain them. An issue in the Canadian Mineralogist in 2011 says that the study off tourmaline shows "that we are standing on the brink of a major breakthrough in the use of tourmaline as a quantitative indicator of the chemical and physical properties of its host environment these properties may well make tourmaline the prime mineral for this purpose." Tourmalines are found in many geological settings. Pegmatites produce many of the specimens cherished by collectors, many of which are pictured here, but they are also commonly found in granites and in metamorphic rocks like schist, shale, marble, conglomerate, dolostone and limestone. Because of their stability they are also found in sedimentary and meta sedimentary rocks. Under diagenetic conditions, tourmaline can develop as overgrowths on detrital tourmaline cores or as new, authigenic crystals.

Of all the different tourmaline species, black tourmaline (schorl) is by far the most abundant and may account for 90% or more of the earth's tourmaline. Schorl tourmaline has the longest history and can trace its description back to a German locality in 1400 and various tin mines in the Erzgebirge. Some are found abundantly in mica schist and some localities can produce thousands of well formed schorl crystals, sometimes of considerable size. They are also found in the cap rock of salt domes as are the povondraite specimens from Bolivia pictured below. At the tin Kami tin mine in Bolivia there are thousands, perhaps millions of tourmaline rich rock associated with the tin veins there. It was so abundant that during the second world war the Japanese, who had great difficulty getting borates, set up a refinery to recover boron from the rocks there. Tourmalines are even found in environments like magnesite deposits, like the one at Brumado in Minas Gerais state, Brazil where they are commonly found as uvite.

Below are listed the current members of the Tourmaline group of minerals. There are two philosophies about naming minerals. One we will call the splitters and the other the lumpers. The splitters want to give a new mineral name to every slight variation of composition and structure. Opposing them are the lumpers who would do away with many of the current mineral names. The lumpers might be personified by the late Dr. Fred Pough, one time curator of the mineral collection at the American Museum of Natural History. On more than one occasion I heard him say approximately this: "Whats the matter with Tourmaline? Tourmaline is a perfectly good name, you don't need all of these varieties to have their own name." Every mineral person worth their salt has their own opinion about what should be done about this mess and, at times, even the IMA at times vacillates back and fourth on the subject. One can't but feel sympathy with the lumpers when confronted with tourmaline crystals like the two immediately below. Each has three different tourmaline species in its structure. Many collectors would like to use one name to name but also feel uncomfortable calling them tourmaline because of the research in recent years has shown clearly that tourmaline is really a group name and not an individual species. If you don't know which tourmaline mineral(s) are represented in your crystal, just call it tourmaline or tourmaline group. However the considerable implications of the composition of various kinds of tourmalines in relationship to what they can tell us about the conditions that formed them and the rocks that host them almost demand that we be more precise about what we call various kinds of tourmalines.

Foitite/rossmanite/elbaite 2.2cm Elba, Italy	© Kohorst

Of all of the many specimens of tourmaline shown below and the links to many others, only a very few crystals of tourmaline have been adequately characterized to determine which tourmaline group mineral(s) they are. In the case of the pink mushroom from Burma above perhaps only two have been characterized. It was found that the predominate tourmaline species near its tip was olenite that graded into elbaite and then into black schorl at its base. It may be that all similar crystals have this same arrangement of tourmaline species in them, but drawing a firm conclusion about them based on such a small sample size is a risky business. Many of the tourmalines shown in this article will never be analysed because to do so would require that they be cut up to gain access to their interiors. The same is true of the crystals from Elba which may contain rossmanite.
Andreas Ertl, John M. Hughes, Stefan Prowatke, Thomas Ludwig, Franz Brandstätter, Wilfried Körner, and M. Darby Dyar (2007) TETRAHEDRALLY COORDINATED BORON IN Li-BEARING OLENITE FROM “MUSHROOM” TOURMALINE FROM MOMEIK, MYANMAR.

There are certainly tourmalines from other localities that have multiple tourmaline species in their structure, but the number of tourmaline crystals that have been accurately characterized is a vanishingly small as a percentage of all tourmalines. Also it is not a simple thing to correctly analyse a tourmaline, you can't just look at the color and know what it is. So when you are looking at tourmalines that have been given specific tourmaline group names, it has been done so on the basis of very few analysis of crystals from any particular locality and in most cases is just a best guess on the part of the collector, curator or mineral dealer. Many pegmatites are rich in fluorine for instance, and in those pegmatites one could expect that some if not all of the tourmalines found at that locality may be the fluor variety. Zoning in tourmalines is common, not only from top to bottom, but from the core of tourmalines outward. Some of this zoning is obvious in transparent and translucent tourmaline crystals and is in fact one of the main reasons why collectors are attracted to them. The more vivid the color change and the more colors a tourmaline crystal has, the more desirable it is to collectors. Studies have shown, that opaque tourmalines, commonly the black and brown ones also can have significant compositional zoning.

Tourmalines are found in many geological settings. Pegmatites produce many of the specimens cherished by collectors, but they are also found in metamorphic environments. Some are found abundantly in mica schist and these localities can produce thousands of well formed crystals, sometimes of considerable size. At the tin Kami tin mine in Bolivia there are thousands, perhaps millions of tourmaline rich rock associated with the tin veins there. It was so abundant that during the second world war the Japanese, who had great difficulty getting borates, set up a refinery to recover boron from the rocks there. It would have been very unpleasant to work in that factory I think. Tourmalines are even found in environments like magnesite deposits, like the one at Brumado in Minas Gerais state, Brazil where they are commonly found as uvites.

Each of the tourmaline group names listed below is linked first to its species page on Mindat and then to an individual Best Minerals article that tells more about each species and in some cases shows many more pictures of that particular kind of tourmaline. To see that article just click on the part of the line that says: "Click here for the Best Minerals XXXXX..."
[Rock Currier 2012]



Buergerite is currently currently not a recognized species. It was recognized as a species in 1966 when specimens were abundant compared to today but, in 2011 was renamed fluor-buergerite because of its fluorine content in 2011. The reason this name is maintained here in the tourmaline group is because of the very many specimens in collections around the world. It will take generations for most of the labels to be corrected.
Henry, D., Novák, M., Hawthorne, F.C., Ertl, A., Dutrow, B.L., Uher, P. & Pezzotta, F. (2011): Nomenclature of the tourmaline supergroup minerals. Am. Mineral., 96, 895-913.


Chromium-dravite: Trigonal: Click here for Best Minerals Chromium-dravite.
Na(Mg₃)Cr³⁺₆(Si₆O₁₈)(BO₃)₃(OH)₃(OH) This is the only picture of Chromium-dravite we have in our database at this time (20 April 2013). The chromium-dravite are the green grains in the rock.




Chromo-alumino-povondraite?: Trigonal: Click here for Best Minerals Chromo-alumino-povondraite.
Na(Cr₃)Mg₂Al₄(Si₆O₁₈)(BO₃)₃(OH)₃O
This is the only image we have of this mineral. It is not clear which part of the image shows chromo-alumino-povondraite and which part is tremolite.




Darrellhenryite: Trigonal, click here for best minerals darrellhenryite.
Na(LiAl₂)Al₆(BO₃)₃Si₆O₁₈(OH)₃O

Mindat lists only one locality for this new tourmaline group member. The type locality for this mineral is Nová Ves, Český Krumlov, South Bohemia Region, Bohemia (Böhmen; Boehmen), Czech Republic. Mindat has no pictures of this mineral (May 2013)



Dravite: Trigonal: Dravite-Elbaite Series, Dravite-Schorl Series. Click here for Best Minerals Dravite.
Na(Mg₃)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃(OH) Quite a few nice specimens are pictured in the dravite article.




Elbaite: Trigonal: Elbaite-Liddicoatite Series, Dravite-Elbaite Series, and the Elbaite-Schorl Series. Click here for Best Minerals Elbaite, Afghanistan to Nigeria and here for Best Minerals Elbaite, Pakistan to Zambia. Many valuable specimens shown here.
Na(Li _1.5Al_1.5)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃(OH)




Feruvite Trigonal: The Fe2+-analogue of uvite. Click here for Best Minerals Feruvite.
Ca(Fe²⁺)₃MgAl₅(Si₆O₁₈)(BO₃)₃(OH)₃(OH)
There are only 14 localities for this tourmaline species but we have pictures of only two specimens from a Japanese locality.




Fluor-buergerite Click here for Best Minerals fluor-buergerite. Mindat currently lists only four localities for this mineral (2013)
Na(Fe₃⁺³)Al₆(Si₆O₁₈)(BO₃)₃O₃F




Fluor-dravite: Trigonal: The F analogue of dravite. Click here for Best Minerals Fluor-dravite.
Na(Mg₃)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃F



A 3.5cm specimens of fluor-dravite from Cream of the Valley Road, Gouverneur, St. Lawrence Co., New York, USA


Fluor-elbaite: Trigonal: The F-analogue of elbaite. Click here for Best Minerals Fluor-elbaite.
Na(Li _1.5Al_1.5)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃F




Fluor-feruvite: The hypothetical F-analogue of feruvite. Click here for Best Minerals Fluor-feruvite.
Ca(Fe²⁺)₃MgAl₅(Si₆O₁₈)(BO₃)₃(OH)₃F
Fluor-feruvite is listed in Mindat's locality database from only one locality: Fort Hope pegmatite field, Fort Hope, Kenora District, Ontario, Canada. We have no images of this mineral and list it as the hypothetical fluorine analogue of feruvite.


Fluor-liddicoatite, Trigonal, the F-analogue of liddicoatite. Click here for Best Minerals Fluor-liddicoatite.
Ca(Li₂Al)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃F




Fluor-schorl: Trigonal: The F-analogue of schorl. Click here for Best Minerals Fluor-schorl.
Na(Fe²⁺₃)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃F




Foitite: Trigonal: A vacancy-dominant member of the Tourmaline Group.
Correct identification is only possible by suitable analytical methods. Click here for Best Minerals Foitite.
(□,Na)(Fe²⁺₂Al)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃OH



A liddicoatite crystal with a foitite cap and a schorl base 8.1mm, Rosina vein, San Piero in Campo, Campo nell'Elba, Elba Island, Livorno Province, Tuscany, Italy



Liddicoatite: Trigonal: Elbaite-Liddicoatite Series. Click here for Best Minerals Liddicoatite.
Ca(Li₂Al)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃(OH)
Note on the nomenclature: the "liddicoatite" holotype (Dunn et al., 1977) is F-dominant on the W-site, although the originally suggested formula was OH-dominant. Therefore the type material has been redefined as fluor-liddicoatite (Henry et al., 2011); "liddicoatite" is currently a non-approved species. Most "liddicoatites" appear to be F-dominant, and therefore fluor-liddicoatite. Note on the nomenclature: the "liddicoatite" holotype (Dunn et al., 1977) is F-dominant on the W-site, although the originally suggested formula was OH-dominant. Therefore the type material has been redefined as fluor-liddicoatite (Henry et al., 2011); "liddicoatite" is currently a non-approved species.



Magnesiofoitite: Trigonal: Click here for Best Minerals magnesiofoitite.
(□,Na)(Mg₂Al)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃(OH)



Huya W-Sn-Be deposit (Pingwu beryl mine), Huya township, Mt Xuebaoding, Pingwu Co., Mianyang Prefecture, Sichuan Province, China


Darrellhenryite: Trigonal: Click here for Best Minerals darrellhenryite.
Na(LiAl2)Al₆(BO₃)₃Si₆O₁₈(OH)_3O

There are no current photos of darrellhenryite on Mindat. Mindat currently lists only one locality for this mineral (May 2013). The type locality for this mineral is Nová Ves, Český Krumlov, South Bohemia Region, Bohemia (Böhmen; Boehmen), Czech Republic.



Olenite: Trigonal: Click here for Best Minerals Olenite.
Na(Al₃)Al₆(Si₆O₁₈)(BO₃)₃O₃(OH)




Oxy-dravite: Trigonal: Click here for Best Minerals Oxy-dravite.
Na(MgAl₂)MgAl₅(Si₆O₁₈)(BO₃)₃(OH)₃O




Oxy-rossmanite: Not yet approved by the IMA. A preliminary working name for a hypothetical new member of the tourmaline group. Click here for Best Minerals Oxy-rossmanite.
☐(LiAl₂)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃O
A preliminary working name for a hypothetical new member of the tourmaline group. Not an IMA approved mineral.



Oxy-schorl: Trigonal: Click here for Oxy-schorl.
Na(Fe²⁺Al)₃Al₆(Si₆O₁₈)(BO₃)₃(OH)₃O
"Schorl" with O>OH,F on the W site; not uncommon, but can be reliably identified only from detailed and quantitative chemical analyses.
Originally used as a working name and published without approval, then finally approved in 2011. IMA status: Approved 2011



Povondraite: Trigonal: Click here for Best Minerals Povondraite.
Na(Fe³⁺₃)Mg₂Fe³⁺₄(Si₆O₁₈)(BO₃)₃(OH)₃O




Rossmanite: Trigonal, Vacancy-dominant member: Identification only possible with quantitative chemical analysis and/or crystal-structure refinement. Click here for Best Minerals Rossmanite.
☐(LiAl₂)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃(OH)



At least its mostly rossmanite. It has a yellow elbaite base with a central portion of white rossmanite with a black foitite cap.



Schorl: Trigonal: Elbaite-Schorl Series, Dravite-Schorl Series. Click here for Best Minerals Schorl.
Na(Fe²⁺₃)Al₆(Si₆O¹⁸)(BO₃)₃(OH)₃(OH)




Tsilaisite : Trigonal: The OH analogue of fluor-tsilaisite. Click here for Best Minerals Tsilaisite.
Na(Mn²⁺)₃Al₆(Si₆O₁₈)(BO₃)₃(OH)₃(OH)




Vanadium-dravite: Synonym of Oxy-vanadium-dravite. Click here for Best Minerals Vanadium-dravite.
Na(Mg,Fe²⁺)₃(V³⁺,Cr³⁺,Al)₆(Si₆O₁₈)(BO₃)₃(OH)₃(OH)





Click here to view Best Minerals and here for Tourmaline group minerals, here for Chromium-dravite, here for Chromo-alumino-povondraite, here for Dravite, here for Elbaite, Afghanistan to Nigeria, here for Elbaite, Pakistan to Zambia here for Feruvite, here for Fluor Buergerite here for Fluor-dravite, here for Fluor-elbaite, here for Fluor-feruvite, here for Fluor-liddicoatite, here for Fluor-schorl, here for Foitite, here for Liddicoatite, here for Luinaite-(OH), here for Magnesiofoitite, here for Olenite, here for Oxy-dravite, here for Oxy-rossmanite, here for Oxy-schorl, here for Povondraite, here for Rossmanite, here for Schorl, here for Tsilaisite and here for Vanadium-dravite. Click here for Best Minerals T and here for Best Minerals A to Z and here for Fast Navigation of completed Best Minerals articles.

Rock Currier
Crystals not pistols.



Edited 97 time(s). Last edit at 05/14/2013 07:04PM by Rock Currier.

Rock,
Thanks for posting this. it is academically interesting, but I even more appreciate the quote from Mr. Pough. Where does the quote end? Is it the whole rest of the paragraph? Sounds like it. I sympathize w/ the lumpers now, but as technology gets better, I'll pity the splitters, because they'll "tilt" from the overload, I suspect! But if it makes 'em happy, fine, more power to 'em. This hobby does get as deep as you want to go...

Hi to everybody!
Ok these are the current members of tourmaline group which are officially recognized as mineralogical species. Nevertheless there is an important problem: how can we distinguish a fluor-dravite from an oxy-dravite and these two species from a dravite? It is necessary to have a chemical analysis and therefore destroy the specimen, at least in the biggest majority of cases! It seems a sort of blaspheme for a gemologist!
Greetings from Italy by Riccardo

D Mike Reinke,
I have put in the missing quote mark. I am not really sure what the final shape of this article will be. Currently I want to get a picture of a tourmaline that George Rossman showed me that had three tourmaline species in it and us that for the lead into the article. Then I think I will put what ever I judge to be the best example of the various tourmalines we have with each of the tourmaline group species listed along with comments about them. I think I will then create an article on each tourmaline group species with a complete an array of the best images we have along with further comments, hopefully helped out by people like you.

Rock Currier
Crystals not pistols.

Ricardo,
I don't know the answer to your question. But your comment is interesting. Perhaps you would care to write it up in a bit more detail with reference to the various tourmaline species? That could very well fit into the article. I am, by the way, willing to post different points of view regarding this. When this is done, I think people reading it will find it more instructive than reading just one point of view. More than likely they will be similar to discussions among the nomenclature group in the IMA.

Rock Currier
Crystals not pistols.