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EducationStibiotantalite and Bismutotantalite Nomenclature

28th Sep 2018 04:46 UTCRudy Bolona Expert

There's Tantalite-(Fe) and Tantalite-(Mn), then why isn't it Tantalite-(Sb) and Tantalite-(Bi)?

28th Sep 2018 08:44 UTCErik Vercammen Expert

Tantalite-(Fe) and tantalite-(Mn) form an isomorphous series, but I think this is not the case for tantalite-(Sb) and tantalite-(Bi).

28th Sep 2018 10:02 UTCJohan Kjellman Expert

Hi Rudy,

Offhand , I think there is a solid solution between stibiotantalite and bismuthotantalite, at least hypothetically, i.e. it could be produced in a lab.

The reason that there is no tantalite-(Sb) and -(Bi), if anyone would propose a name change, is rather that the root-name "tantalite" is already claimed by another structure, the columbite-(tantalite) structure.

cheers

28th Sep 2018 12:57 UTCJolyon Ralph Founder

Sitbiotantalite and Bismutotantalite aren't directly related to tantalite.

28th Sep 2018 16:48 UTCTravis Olds Expert

Odd that the same specimen is listed as both tantalite-Mn and stibiotantalite in header photos for these..

https://www.mindat.org/photo-66752.html is header on https://www.mindat.org/min-8669.html

https://www.mindat.org/photo-259794.html is header on https://www.mindat.org/min-3739.html

29th Sep 2018 01:05 UTCPavel Kartashov Manager

I am absolutely not surprised by deep mineralogical knowledges of Rob, but, frankly speaking, I didn't expect such question from Rudy. Such question as IFF signal tell me, that the one of the best tantaloniobates collection is in hands of guy, who don't knows tantaloniobates. Such question is similar to "How much chlorine is in chlorite and actinium in actinolite?" :-(((((

29th Sep 2018 08:33 UTCTravis Olds Expert

Not to distract from the original topic, but it seems the "most dangerous" tantaloniobate identifications, as you allude to them in a separate post, Pavel, are not analyzed samples but rather some unanalyzed high-end pieces that still sit prominently on the main pages for these series. I'm still salty my ugly little analyzed tantalite-(Fe) from Michigan was called into question and removed from the galleries while these huge euhedral crystals remain incorrectly placed, presumably for their looks..?

But back on topic.. The crystal structures of tantalite-(Fe) & -(Mn) vs. stibio- & bismutotantalite are geometrically very similar but the latter two have different space groups and slight structural peculiarities that set them apart. Same applies to columbite-(Fe) -(Mn) vs. stibio- and bismutocolumbite. Each of their structures contain sheets of corrugated Ta/Nb octahedra that sandwich the suffix or prefix-defining cations that are arranged into zig-zagging chains; i.e. the Fe/Mn (also octahedra) and Sb/Bi (irregularly shaped 6-coordinated polyhedra). See comparison photo of the chains of irregular Bi in bismutotantalite and Mn octahedra in tantalite-(Mn). So in addition to the different polyhedron shapes, there is a significant size difference between Sb3+ and Bi3+ (more prominant than Fe vs Mn) and unique arrangements of lone-pair electron that causes the differences. This info is from:

http://rruff.info/doclib/cm/vol39/CM39_103.pdf

29th Sep 2018 08:37 UTCJolyon Ralph Founder

I fixed the photo

29th Sep 2018 10:57 UTCJohan Kjellman Expert

Keep asking whatever questions you may have Rudy!

Excellent taste, and extraordinary field skills, in mineral collecting does not necessarily equate with in-depth knowledge of structural mineralogy or crystal chemistry. We come from all over, I am surpriced you wasn't aware of that Pavel:)

cheers

29th Sep 2018 21:31 UTCPavel Kartashov Manager

We with Rudy are familiar about 8 years. I am suppose, not too much guys here able to appreciate high class of Rudy's collection as me able. Therefore, Rudy does not need protection from me. I was just surprised and wrote about it. Without a correct understanding of the nomenclature, it is impossible to create a correct and complete systematic collection. Difference between metrics AB₂O₆ and ABO₄ is enough obvious, to try joint them in the same systematic taxon.

I am not completely understood Travis's position. I am afraid I didn't underand the first part of his post. What about the second one, it should be understood that the structures of half of the cubic minerals (for example) are constructed on the basis of the structure of NaCl. However, this does not serve as a reason to build a group of pyrite-galena or cuprite-pyrochlore. Structures of many tantalo-niobates are built up on basis of ruthile or brookite structures, and has similar chains of polyhedrons. In itself this does not prove anything.

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