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Improving Mindat.orgAllanite?, Trimouns Talc Mine

16th Feb 2015 08:00 UTCOlav Revheim Manager

Please see this gallery: http://www.mindat.org/gallery.php?loc=1745&min=125 and the following quote form the allanite best minerals article:

"Peter Haas observed, "Some of the big "allanites" later turned out to be dissakisites ! " and Pavel Kartashov replied. "It would be more exact to say, that almost all allanite-(Ce) from Trimouns turned out dissakisite-(Ce). Real allanite-(Ce) form here form only dark-coloured zones within transparent light-coloured dissakisite xls." All the brown "Allanites" are Dissakisite-(Ce) (RWMW edit)"

Are there any of the allanites that should NOT be moved to the dissakite-(Ce) gallery?

Olav

16th Feb 2015 13:56 UTCReiner Mielke Expert

Hello Olav,

You are braver than I am (tu). This is like throwing a stink bomb into a crowd. :-D

16th Feb 2015 14:14 UTCOlav Revheim Manager

Thank you Reiner,

I think that moving photos from a common mineral to a rare mineral is easier to accept than the other way round :)-D

Olav

16th Feb 2015 17:51 UTCRob Woodside 🌟 Manager

http://www.mindat.org/photo-117683.html , http://www.mindat.org/photo-39026.html , http://www.mindat.org/photo-39026.html

There are layered intergrowths of tetrahedride and tennantite from Mexico and many other examples. How to label them with a single name? You can't do it honestly. The darker entries may contain more allanite than the lighter ones. and here's a dark one posted as Dissakisite-(Ce).http://www.mindat.org/photo-339221.html This one doesn't show the dark allanite bands, so it may be alanite or close to it, since there is a series between these minerals. However like with annabergite and erythrite the colour change may not happen at the 50/50 mark where the IMA says the species change. I'll change my caption to contain both.

16th Feb 2015 18:47 UTCOlav Revheim Manager

Thank you Rob.

I found the article also, see http://www.researchgate.net/publication/50982131_Dissakisite-(Ce)_chemical_composition_some_implications_for_its_origins.

I think I'll make a note on the locality page, and also in the caption of the photos that both minerals are probably present in all crystals. I think I'll place most of the photos in the dissakisite-(Ce) gallery. Since the article clearly states that "Back-scattered electron (BSE) images reveal that each of the described dissakisite crystals has three distinct compositional zones" I am not sure that listing them as a series will be entirely correct either.

Thanks

Olav

25th Feb 2015 13:11 UTCGeorges Favreau Manager

Dear all,

Dissakisite-(Ce) may be more abundant than previously thought (like wendwilsonite in Bou Azzer).

But before generalizing the conclusions to "almost all" or "all" crystals, is it possible to know how many samples were studied?

The Japanese article refers to the analyzed "sample" (only one?).

As many of us know, the Trimouns quarry is very large, the composition and look of dolomite very variable, and mining operation/collecting have been done over decades.

In these conditions, can we have global conclusions?

Best wishes,

Georges.

26th Feb 2015 09:09 UTCOlav Revheim Manager

George,

Thank you for chiming in on this discussion. It would obviously be good to have more analyses available for this material, especially as it seems to be relative abundant.

The Japanese article presents data from multiple crystals from one sample, which is a rather limited amount of data.

Unfortunately, the collectors and dealers uploading photos to mindat face the challenge of putting a name to the specimen displayed on their photo. They have no other option than naming their specimens based on available information, and at present it seems that the names allanite-(Ce) and dissakisite-(Ce) are applied rather randomly by the individual uploader. This is a very typical issue for many minerals that can only be distinguished via individual analysis, and for the "allanite-(Ce)"and "dissakisite-(Ce)" from Trimouns, the REE contant may be variable, the Mg/Fe²⁺ ratio and the Fe³⁺/Fe²⁺ ratios may be variable even within the same crystal. Even when the composition of a crystal are known, errors can be done normalizing the formula. The latter unfortunately also happen in scientific journals.

Many articles have been published on the REE bearing minerals from Trimouns, including yours printed in Lapis. These include:

- de Parseval, P., Fontan, F., Aigouy, T. (1997): Composition chimique des minéraux de terres rares de Trimouns (Ariège, France). C. R. Acad. Sc. Paris, 234, Sér. IIa, 625-630.

- Marty, F. (2004). "The Trimouns quarry, Luzenac - Ariège - France." The Mineralogical Record, 35(3), 225-247+274.

- Gatel, P. , Parodi, G. , Parseval (De), P. , Fontan, F. and Marty, F. (2002). "Les minéraux de terres rares à Trimouns." Le Règne Minéral(Hors série 8), 29-63.

- Gatel, P. , Parodi, G. , Parseval (De), P. and Fontan, F. (2002). "Les minéraux de terres rares (T.R.)." Le Règne Minéral(Hors série 8), 20-28.

- Gatel, P. and Marty, F. (2002). "Autres espèces de Trimouns." Le Règne Minéral(Hors série 8), 64-76.

- Gatel P:(1990): Trimouns (Données complémentaires sur les espèces minérales du gisement de talc de Trimouns ) Le Cahier des Micromonteurs , 4, p.3,8-12

- de Parseval, P., Fontan, F., and Aigouy, T. (1997) Chemical composition of REE minerals from Trimouns (French Pyrenees). Comptes Rendus de l’Academie

des Sciences, 324, 625–630.

and possibly also

Philippe de Parseval (1992) Etude minéralogique et géochimique du gisement de talc et chlorite de Trimouns (Pyrénées, France), Thèse de doctorat : Minéral.-Géochimie : Toulouse 3 : 1992 ; 1333.

Hopefully some of these may include analyses of the "allanite-(Ce)"/ "dissakisite-(Ce)", which could provide a better basis for assigning names to these specimens. I would appreciate if anyone could share a copy of these articles with me, or check if microprobe results for the "allanite-(Ce)"/ "dissakisite-(Ce)" are included, or even share the author's e-mail addresses with me in a PM.

Olav

2nd Mar 2015 16:10 UTCKnut Edvard Larsen Manager

The best global solution would be to label all non-analyzed samples as a "Allanite Group Mineral", http://www.mindat.org/min-46220.html

_____

From Marty, F. (2004), the follwing info are given: ( p. 232)

"Allanite and dissikaite are chemically similar, and are distinguished primarily on the basis of the Fe:Mg ratio. Individual crystals tends to be rather homogenous; many line scans carried out by a scanning out by a scanning electron microscope (SEM) analysis of a crystal and the corresponding diffractogram for the same crystal demonstrate this (Pinato, 1999).

The reference is a master thesis: Pinatto, J. (1999-2000): Etude des minéraux complexes du gisements de Trimouns (Ariège): Master thesis, Université d'Orleans, France, 1-26.

2nd Mar 2015 20:04 UTCOlav Revheim Manager

Thank you Knut Edvard

Olav

2nd Mar 2015 21:01 UTCRob Woodside 🌟 Manager

O.K. Allanite gp is a single name that fits both.;-) I added Allanite group to the species list.

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