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Identity HelpYttrocrasite-(Y) from Kibara Mts, D.R. Congo?

28th Oct 2013 11:30 UTCVik Vanrusselt Expert

Hello all,

I got this Yttrocrasite-(Y) specimen today. The label says it's from "Monts Kibara, 100km south of Manono, Katanga, Congo".

I found a reference to the mountain range here: http://en.wikipedia.org/wiki/Kibara_Mountains

Which of the localities on Mindat could this be attributed to? Or should I just upload it under "Katanga"?

Yttrocrasite-(Y) is not in the mineral list for Katanga, though.

Any help is greatly appreciated.

Vik

28th Oct 2013 12:02 UTCRik Dillen Expert

Here are some references to the occurrences of e.g. cassiterite, wolframite, tantalite, rare earth minerals etc. in the Kibara Mountains, a region that is well known for this kind of minerals. :

http://www.walter-pohl.com/news.html

http://pubs.usgs.gov/pdf/circular/c930-o.pdf

http://petrology.oxfordjournals.org/content/45/4/669.full

http://www.geologicabelgica.be/PDF/Journal/vol1612/DEWAELE_2013.pdf

Grts,

Rik Dillen

29th Oct 2013 11:20 UTCPavel Kartashov Manager

I am think, that the mineral in reality is euxenite-(Y).

29th Oct 2013 12:56 UTCSpencer Ivan Mather

I agree with Pavel on this one...

Spencer.

29th Oct 2013 15:42 UTCRik Dillen Expert

Hi Pavel and Spencer (et al., of course),

What are your arguments to doubt the original label in favor of euxenite(Y) ?

On sight re-identification just via a photo is highly risky !

In the meantime I did some research in the literature, and found out that

1) yttrocrasite has indeed been found in Mitwaba (published : 1956 ‘‘Mesure de l’âge de l’yttrocrasite de Mitwaba (Katanga) par la

méthode au plomb. II. Mesures isotopiques’’; in collaboration with P. Eberhard, J. Geiss, H.R. von Gunten and P. Signer; Bull. de la Soc. Belge de Géol., de Paléont. et d’Hydrologie, Bruxelles, tome 65, 251–256. I don't have the complete article at hand here, but an abstract can be found via the internet (just google "Yttrocrasite, Mitwaba"). A lot of Belgian geological and mineralogical research has been performed in this area.

2) Mitwaba is a well-known locality in the Kibara range - if you put in "Mitwaba" in Google maps you will end up at almost the same place as when you put in "Kibara montains".

3) Neither the fact that the Kibara range and/or Mitwaba are not mentioned in the localities list of MINDAT is an argument to doubt the original label (some tens of thousands of other localities are missing too), nor the absence on MINDAT of yttrocrasite as a mineral occurring in Congo is an argument.

So my conclusion is : the locality can even be refined to Mitwabe, Kibara mountains, 100km south of Manono, Katanga, Congo, and there is IMHO no reason and/or argument to rename it to euxenite-(Y) or whichever other mineral name. Of course, if an analysis would prove that the specimen has been misidentified it should be re-labeled.

As usual, my point of view stays valid until the moment that someone proves that I'm wrong :>)

Best regards,

Rik Dillen

29th Oct 2013 17:01 UTCReiner Mielke Expert

It seems that Yttroclasite as a species is questionable, the most recent paper on the subject referenced by mindat (American Mineralogist (1982): 67: 156) says that the original data defining the species by Crook 1977 is erroneous?

As such questioning the ID of this sample is not unreasonable and just based on probability alone it is far more likely to be euxenite, not that it is, that needs to be determined by analysis.

29th Oct 2013 17:15 UTCRob Woodside 🌟 Manager

Were all of Wilson Crook III's minerals discredited or just the really outrageous ones? He seems to have become an archaeologist.

29th Oct 2013 20:28 UTCRik Dillen Expert

Even if certain authors/researchers claim that a species is "questionable", we should leave the decision to the CNMMN of the IMA. As long as yttrocrasite-(Y) is not discredited officially, it stays a valid species.

BTW that "Crook" is the same person who described years ago the "mineral" texasite, that was later on proven to be a piece of a man-made Pr-oysulphate. Obviously he has not stolen his name :>))

Please note :

- yttrocrasite was not discovered by Crook, but by Hidden and Warren in 1906 ("On yttrocrasite, a new yttrium-thorium-uranium-titanite", Am. J. Sci. 22, 515-519)

- Crook analysed (what he probably did not :>) material from another source than the material that was described by Hidden and Warren, as the type locality is inundated since 1936. Therefore the - correct or not - data of Crook do not tell anything about the original material that was described by Hidden and Warren.

- Peacor et al. ("New data on and discreditation of "texasite," "albrittonite," "cuproartinite", "cuprohydromagnesite," and "yttromicrolite," with corrected data on nickelbischofite, rowlandite, and yttrocrasite", Am. Mineral. 67, 156-169, 1982) do not discredit yttrocrasite, but report "corrected data"

Bear in mind that, even if some or several data would be wrong and/or inconsistent, the species yttrocrasite-(Y) could still be a valid separate species.

We cannot decide on our own to rename a species based on a feeling that maybe some data are wrong. There is a commission installed to investigate such cases thoroughly and to take an official decision.

So until further notice from the IMA for me yttrocrasite-(Y) stays a valid species.

Greetings, Rik Dillen

29th Oct 2013 20:36 UTCRob Woodside 🌟 Manager

Thanks Rik !!! That should be an article.(tu)

29th Oct 2013 20:45 UTCJohan Kjellman Expert

I don't think yttrocrasite was ever approved. It was described in the early 1900's and thus "grandfathered". Then "the crook" came along in 1977 and did his "job". But I suppose you can't discredit a mineral just because a crook has tried to "refine" it, i.e. it was only Crooks work that was discredited and the mineral was just as before "grandfathered". Then a big mistake was made in 1987, when a "truckload" of older species became "approved" after an article (Am Min 72, 1031) on the renaming of minerals according to the Levinson rule.

For a discussion on this see: http://www.mindat.org/forum.php?read,14,112462,113873#msg-113873

You can self check the list here in appendix 2 http://www.minsocam.org/ammin/AM72/AM72_1031.pdf

(The point made by me is that many minerals got erroneously "approved" when they in reality were only RENAMED.)

There exist two YB₂(O,OH)₆ minerals with Ti dominating the B-site and they are aeschynite-(Y) with aeschynite structure, and polycrase-(Y) with euxenite structure. I am not certain if they are formally approved but they are firmly established within the small group of mineralogists that work with these substances. A third species - yttrocrasite? - would only be required if there was a third structure firmly established.

What more..., oh yes, in the aeschynite-(Y) samples from the Western Alps discussed by Bonazzi and Menchetti (Eur.J.Min 1999, vol 11, pp.1043-49) these B-sites are full or nearly filled with Ti (as the original yttrocrasite). Essentially this is achieved by the substitution of O by OH.

cheers

29th Oct 2013 21:34 UTCRudy Bolona Expert

How long did it take for these types of minerals to go from definite structure to "metamict soup" If we had a time machine and we collected some 100 years after they crystallized, what would we have?

29th Oct 2013 21:59 UTCJohan Kjellman Expert

Rudy,

Probability says that we'd have found a mineral with euxenite or aeschynite structure, i.e. if we are talking about the yttrocrasite.

How long to decompose, depend on U and Th content.

cheers

2nd Nov 2013 21:29 UTCPavel Kartashov Manager

I had say only, that I am will not great surprised if the specimen being analysed will show usual for euxenite high Nb contents.

The last article on yttrocrasite-(Y), which I know, was written in 2005 - http://www.geo.komisc.ru/images/stories/vestnik/2005/132/pdf/132_3-4.pdf (The first find of yttrokrasite at Prepolar Ural) about such samples - http://www.mindat.org/photo-70465.html

2nd Nov 2013 23:41 UTCReiner Mielke Expert

So how low does Nb have to be to call it Yttrocrasite-Y rather than say Polycrase-Y or Aeschynite-Y? Do these three form a continuous series with Euxenite-Y?

3rd Nov 2013 03:29 UTCPavel Kartashov Manager

First of all, yttrocrasite is euxenite group member, and aeschynite here is out of topic.

According to my own, personal, subjective point of view at euxenite group, there are only three real minerals on the Nb-Ti side of the triangle Nb-Ti-Ta : Fersmite Nb₂ - Euxenite TiNb - Yttrocrasite Ti₂.

Polycrase is excessive intermediate indistinct phase, the same as blomstrandine/priorite (analogues of polycrase) and nioboaeschynites in aeschynite group.

3rd Nov 2013 10:19 UTCJohan Kjellman Expert

Just as you (?) Pavel I am not certain that the final classification have reached an elegant solution yet. I am a bit surprised though about your statement that yttrocrasite definitely belongs to the euxenite group/structure. But I have also a very bad memory so maybe you can remind me of the article that established this structure to the original yttrocrasite from Texas.

Also why is the aeschynite-structure out of the question? If my weak memory serves me right Ti has a stabilizing effect on the aeschynite structure.

It would also be interesting to hear you elaborate on your subjective view of the euxenite group, you mention only the B cations, what complete formulas are you inferring to?

These?

CaNb2O6 fersmite

YNbTiO6 euxenite

YTi2O5OH yttrocrasite

What about uranopolycrase UTi2O6? And, in case all these formulas are valid/possible, shouldn't we also contemplate CaNbTiO5OH?

From what I remember the yttrocrasites reported are metamict with Ln:Ti ratio 1:2 and Nb very low. The only article I can recall from memory that reports an Ln-Nb-Ti-oxide with "yttrocrasite-chemistry" AND a confirmed structure is the article on aeschynite from the alps.

cheers

3rd Nov 2013 11:32 UTCReiner Mielke Expert

As I see it the problem is that most of these are metamict and no longer have a structure that can be clearly defined, that leaves only chemistry. It seems to me that what is needed is a parallel system of classification for metamict minerals based purely on chemistry, that would solve a lot of problems.

5th Nov 2013 04:57 UTCPavel Kartashov Manager

Dear Johan,

conventionally was stated that metamict REETiNbO₆ belong to euxenite group when U>Th, and to aeschynite group when Th>U. Indeed ThO₂ content in aeschynites usually is around 10%, often ~15%, and not to rare about 20-25% with very insignificant amounts of UO₂ or absence of it.

From this point of view initial yttrocrasite from Texas is typical euxenite group member.

Aeschynite-structure out of the question because of it is need in its own aeschynite-group nomenclature. But the group consist for the moment only from 4 real members - aeschynite-(Ce), -(Nd) and -(Y) and tantalaeschynite-(Y). Of course, this nomenclature will be mirror reflection of euxenite group one, but with different members. But strategy will be the same.

These nomenclatures are completely characterised by two triangles Nb-Ta-Ti and REE&Y-Ca-U&Th. So you mentioned proper formulas of 3 end members of euxenite group.

Uranopolycrase is absent on the first triangle, but take its lawfull place in the second triangle corner (lower right).

Of course you may to contemplate CaNbTiO5OH end member, but you should to understand that its role in nature is the same as skiagite and hogarite end members in garnet group or Th_0.5TiO₃ in perovskite group.

Yttrocrasite from Ural is crystalline enough and its structure can be solved. Simply somebody should to do this.

5th Nov 2013 05:30 UTCAlfredo Petrov Manager

Rik, I must disagree with you on one point: We are not obligated to consider a mineral to be a valid species if there is little or no evidence for its distinctiveness - especially in the case of pre-IMA ("grandfathered") species. Contrary to what many collectors think, "grandfathering" is not the same thing as "validity". The IMA did not automatically approve all pre-1959 minerals as "valid", it just declined to vote on them and accepted everything "generally considered" to be valid - So the validity of "grandfathered" minerals like quartz and native gold was never in question, obviously, as everyone considers them to be valid. "Grandfathering" was not an action on the IMA's part, it was the absence of action. So when serious questions are raised about a pre-1959 mineral, and some people stop believing it to be a species, then it is no longer "generally considered valid" and so ceases to fulfill the criteria for "grandfathering". The burden of proof then falls on those who still consider it to be valid. Anything else would be analogous to zoologists still keeping unicorns on their lists of approved species just because no one had yet formally disproved their existence. Mineral species lists have quite a few "unicorns" in their ranks. Belief is optional :-)

5th Nov 2013 10:50 UTCJohan Kjellman Expert

Thanks Pavel for reminders.

However, isn't it so at present that the formal rules of nomenclature states that it is changes of a dominating element in a site that validifies a namechange? Thus, at present and contrary to your subjective thoughts, there are three minerals in the euxenite group with Y at the A-site: Euxenite with Nb dominating the B-site, polycrase with Ti and tanteuxenite with Ta dominating. In general one can also say that partial "fersmitic" and "uranopolycrasic" substitutions are usually responsible for the wobbling towards Nb- or Ti-dominance at the B-site. In this scenario yttrocrasite is "just" an extreme polycrase and thus questionable.

It would be interesting to hear your further thoughts on "your" nomenclature. When does a euxenite become an yttrocrase (or polycrase)?

cheers

5th Nov 2013 10:59 UTCRik Dillen Expert

Alfredo (et al.), of course "grandfathering" is not the same as "validity". But because of the principle of grandfathering those minerals are validated as such until the moment that an official renaming procedure is undertaken. I understand the logic your point of view, but that could end up in some kind of anarchy. What is the limit where we speak of "generally considered valid" (or the opposite) ? Sometimes it is better to have rules that are not perfect, than to have no rules at all or rules that are not applied. I agree with your way of thinking about "grandfathering", but if new data would suggest that a species has to be renamed, the right path to follow is to propose the change to the IMA and to start to use the new name or nomenclature only from the moment it is officially validated. That avoids also a sequence of discreditation and recreditation, which happened already before. What if some group would attribute a new status to yttrocrasite-(Y), and others would put it rather in yet another group ? Or perhaps the IMA could even decide to revise the whole surroundings of the group of related minerals. So prejudging based just on opinions (even if a large group of scientists/curators think so and/or the data to support the opinion are valid and correct), is IMHO not to be recommended.

Even if a law has been proven to be stupid, it has to be obeyed until the government changes it :>)

Anyway, that is my opinion.

5th Nov 2013 11:20 UTCAlain Hanson Expert

Hi Vik

Yttrocrasite from Mt. Kibara is originaly listed in pg 407 of H . Buttgenbach, 1947 Les Minéraux de Belgique et du Congo belge on basis of an analysis given : SiO2,1,2, TiO2 50,0, Fe2O3 5,2, U3O8 6,1, Al2O3 4,2 Y2O3 18,2, Ce2O3 + CaO 4,3, LOI 5,5 Sum 94,7

But MRAC collections show no Yttrocrasite or Euxenite from Mt. Kibara but only 3 samples for that location matching the description of your sample ( see MRAC collections ) those 3 are identified as Aeschynite from Mitwaba, Kibara Massif, Katanga, RDC.

Not sure of the method for naming them, since the MRAC records show no XRD performed or analysis or XRD after heating

Just hope this helps

Alain

5th Nov 2013 13:07 UTCJohan Kjellman Expert

Rik,

It is for sure grandfathered but as such listed as "questionable", probably for several good reasons. In the general case of such "beasts" and their possible revival, one should have a very good case.

Pavel,

Back to our speculations on the identity of "yttrocrasite". I see now that the material originally described from Texas did in fact have Th much dominant over U. Thus, I think we really cannot tell at this point what is certain regarding the structure of the original material, or are you now convinced that the original yttrocrasite had an aeschynite structure?

The Russian material have slight dominance of Th over U and the Congo material only U. The Congo analyses is bad, incomplete and leached, by the way and not much to build on. But I am with you that this is more "euxenite" than aeschynite. By the way, the totals of the Russian mineral is also quite low.

In conclusion, when talking about yttrocrasite, I am in favour of talking only about the original (questionable) material, which has a total of about 95 wt% when H2O is deducted. It has a high Th content suggestive of originally having an aeschynite structure, this is consistent with the aeschynites from the alps. However, I wouldn't rule out "anything" at this point.

The Russian and Congo material have totals around or below 90 wt %. They are different, or inconclusive regarding the minor elements, and the names have been attributed (I suppose) because of the similarities of the general cationic ratios Y:Ti = 1:2 of the major constituents. In my opinion, these samples do not really contribute to our understanding of yttrocrasite.

cheers

5th Nov 2013 23:32 UTCPavel Kartashov Manager

Yes, I was completely wrong. Yttrocrasite is aeschynite group member.

I was out, because mineral on Vik's photos looks like euxenite exactly.

What about "absence" of Nb in initial yttrocrasite analysis (and analysis material from Kibara), it absolutely don't means that Nb and Ta really are absent in the minerals. Old wet analyses were unable correct to divide Ti from Nb and Ta. Analytycal methods of wet cemistry, able surely divide Ti, Nb and Ta from their mixture, were invented only in the end of 50th. So, faster of all, the initial yttrocrasite had contains some of both Nb and Ta.

The same situation with U and Th. I am not sure, that Th was analysed in Kibara material at all.

I should to found my own analyses of yttrocrasite from Ural. I don't remember their totals. But in the article the most reliable is the third analysis performed under 25 kV. I also made them under such voltage (it is the best for heavy matrixes such as tantalo-niobates).

By the way, according to "50% rule", both euxenite and aeschynite are invalid species.;-) According the rule, intermediate species on 50/50 points of triangle are valid minerals only when they show structural ordering (for example dolomite CaMg(CO₃)₂ on calcite-magnesite side of Ca-Mg-(Mn or Fe) triangles). But both euxenite and aeschynite don't demonstrate us such ordering - they are completely isostructural with members of theyr groups.
So present nomenclatures of both aeschynite and euxenite are in direct and dramatic contradiction with basic rule/principle of modern mineralogical nomenclature. So :)-D for the repose of euxenite and aeschynite souls...:-(:-(:-(

19th Feb 2015 15:45 UTCVik Vanrusselt Expert

Pavel (et al.),

if anyone would like to do a (non-destructive) analysis on my specimen (for a fee if necessary), send me a private message with your address (and payment options) and I will send it to you.

Vik

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