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LocalitiesHopffeldboden, Hopffeld area, Neukirchen am Großvenediger, Zell am See District, Salzburg, Austria

20th Feb 2019 06:22 UTCChristian Auer 🌟 Expert

I am wondering why all of these are called euxenite-Y https://www.mindat.org/gallery.php?loc=12771&min=1425 and these polycrase-Y https://www.mindat.org/gallery.php?loc=12771&min=3257 (one picture includes also tanteuxenite-Y https://www.mindat.org/photo-420249.html ). None of them mentions any ID method (which would be even difficult due to the probably metamict character) and I doubt you can determine them by your eye (all orthorhombic xtls).

Wouldnt it be fair to add them all into the euxenite group https://www.mindat.org/min-47564.html ?

22nd Feb 2019 06:11 UTCChristian Auer 🌟 Expert

Noone ever had to do with minerals from the euxenite group?

Is it possible to determine them with their xtl end faces as its done by collectors of the Hopffeldboden?

Due to the metamict character I tested one xtls with SEM-EDS:

Nb 18 Y 9 U 1 Ta 1 Gd 1 atom% which would lead me to euxenit-Y

22nd Feb 2019 07:17 UTCKeith Compton 🌟 Manager

As an aside why do we have "Hopffeld area" as part of the locality string? Appears totally irrelevant to me. Perhaps someone with local knowledge can add a reason, but I suggest removing it.

22nd Feb 2019 07:42 UTCChristian Auer 🌟 Expert

No Keith this makes sense.

See kainosite for example. It was erroneously reported from the Hopffeldboden but can be found in the steep Hopffeld Graben locality.

The Hopffeld area is the link between both.

22nd Feb 2019 08:30 UTCKeith Compton 🌟 Manager

That to me makes the Hopffeld area redundant, rather than justifying it.

What then is the locality ... Hopffeld .. is this a place ? This is also suspect to me.

I haven't seen "Hopffeld area" in the literature either.

When searching Google for example the only meaning ful references to these two appear to be Mindat and that doesn't auger well to me at least.

I would propose to remove both 'Hopffeld area" and "Hopffeld".

22nd Feb 2019 13:48 UTCJohan Kjellman Expert

If "complete" your analysis shows Y+U+Gd= 11, Nb+Ta= 19, thus a simplified ratio of Y:Nb = 1:2

thus YNb2 positive charge 13 requires 6.5 O

euxenite and aeschynite minerals are YTiNbO6

your formula suggests a pyrochlore group mineral ◻YNb2O6(OH,F)

why not consult the article connected to some of these images?

Non-metamict REE-Nb-oxides of alpine origin are not unheard of - how old/young is this deposit?

traditionally, for example in Norway, euxenite an aeshynite crystals, both orthorhombic, are separated by morphology.

cheers

23rd Feb 2019 11:16 UTCJohan Kjellman Expert

sorry - I misunderstood the question

yes all these species belong to euxenite group

distinction between species ought to have been done based on chemistry - eds?

cheers

3rd Mar 2019 07:28 UTCUwe Ludwig

The "Hopffeldboden" is a verry important location of the Hohe Tauern mountains. For further explanation I enclose a pisture. The Hopffeldboden is the gras land in the middle. The material comes down from the light coloured rock above. The Hopffeldgraben is the little valley on the right side. The material of this location comes from the alps on the upper part and is different of the rocks of the Hopffeldboden. So Hopffeldboden and Hopffeldgraben have similar sounding names and are near together but have different rocks and of course differend minerals.

Rgds.

Uwe Ludwig

3rd Mar 2019 19:35 UTCFred E. Davis

I found this article useful in sorting out EDS data when dealing with (Y,REE,U,Th)-(Nb,Ta,Ti)-oxide (including metamict) minerals:

Ercit, T. S. 2005. Identification and Alteration Trends of Granitic-Pegmatite-Hosted (Y,REE,U,Th)-(Nb,Ta,Ti) Oxide Minerals: A Statistical Approach. Canadian Mineralogist 43:1291-1303.

4th Mar 2019 07:21 UTCChristian Auer 🌟 Expert

Thank you very much Fred, I just downloaded the article from researchgate and will read it.

4th Mar 2019 10:47 UTCJohan Kjellman Expert

Christian,

To go back to your original questions. All the minerals belong as you say to the euxenite group, which has the general formula of AB2O6, and the species division is made by chemistry. For all these species Y is the dominant cation on the A-site which thus has a charge of 3. For charge balance reasons the two cations on the B-site have then an average charge of 4.5, which is usually occupied by one cation Ti and one pentavalent, Nb or Ta. For compensations of minor substitutions the Ti or Nb and Ta may dominate the B-site.

The species division is then idealized.

euxenite Y(NbTi)2O6

polycrase Y(TiNb)2O6

tanteuxenite Y(TaTi)2O6

The answer to your question why these are found in different galleries, I suppose then, is that people made chemical analyses indicative to the species in question. There is no way that these species, especially if they are metamict, can be directly indicated by x-ray or morphology. But, of course, indirectly if someone has made a systematic investigation that correlates morphology with chemistry.

cheers

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