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Betafite

Posted by Rock Currier  
avatar Betafite
November 02, 2009 11:06AM
©


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This article is a place holder and needs someone to take it in hand and finish the first draft. If you would like to take this article in hand, leave a reply message below or contact Rock Currier via private message by clicking on the PM button next to my name at the top of the article.



This Article is Under Construction




Click here to view Best Minerals B 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? After each set of pictures there should be some descriptive text. If none appears it means that we need someone to tell us about the specimens from that locality and something about the geology of the occurrence.

Betafite
(Ca,U)2(Ti,Nb)2O6(OH) isometric

Betafite, Silver Crater Mine (Basin Property), Faraday Township, Bancroft District, Hastings Co., Ontario, Canada xl=2.1cm wide© Jay Vonderhey

Here we need to put general comments about Betafite specimens in general.


Betafite
Canada
Ontario, Hastings Co., Bancroft District, Faraday Township, Silver Crater Mine (Basin Property)

Betafite crystal, 4cm wide© Rob Lavinsky
Betafite, 2.3 cm wide© 2002 John H. Betts


Betafite, 2.3 cm wide© 2001 John H. Betts
Betafite, 7cm wide© Joseph A. Freilich


Betafite, 2cm wide© Jay Vonderhey
Betafite, 4.5 cm wide© Joseph A. Freilich





I don't know if any of you read an old reporting I did on Silver Crater, but back about 43 years ago, I was there collecting on a Gemboree arranged field trip, and the widow of the original owner had had the basin scraped to bedrock basically, by a dozer, and we went in there with a fresh slate. A lady american mineral dealer, and a couple from Burlington Ontario both found circular holes filled with black muck very near the center. They started digging before lunch and at around 4 they had both mined out the u-shaped tube to the bottom. The results were about 5x5 foot trestle tables covered with crystals of Betafites for the Burlington couple and a large wheel barrow filled to the brim for the lady dealer...and these were all free floaters ranging from pea sized to 3" and larger perfect singles and multiples...all nicely protected and preserved by that awful black mire. The lady mineral dealer when I asked her what she felt she had in specimens, stated that maybe about 100 thousand would be fair market value, and this was back in the 60's . I have never seen such a haul before or since, with the exception of the pit in St Hilaire that produced those spectacular serandites, or maybe the collecting of garnets at River Valley near N. Bay, Ontario. I always wondered what became of all those hundreds of Betafites...
[Ray Hill 2009]

When we collected there back in the 90's you paid $2. to cross the property, and the road to the mine was nicely marked with little arrows to follow as it wound through the woods back at least 1/2 mile to the mine. We were able at that time to drive right up on to the hill which is basically soild calcite. We parked up over where the adit goes under the hill. The reddish haloes do surround the areas where the mose betafites are found, but this is hard to see on the surface. It's mush easier to see what is going on by going into the adit and looking at the calcite there. The adit goes straight into the calcite body for a few feet, then there is a "crossroad" to the left and right, with a drift going up into the calcite. Looking at the walls in there you can see how the betafites cluster in zones. There isn't really anything to work inside the mine. I'm telling you this to save you the trouble of going in yourself, because God only knows how much radon there is in there. I spent as little time as possible and got out to work outside. On our first trip we tried to break up the calcite and found a few betafites, small ones up to a half inch or so, and some apatite, biotite, and hornblende crystals. The betafites are very brittle and easy to break, most of the time when you break the calcite you come up with two pieces, each with a half of the betafite crystal. On our second trip we had some good success by finding where there were betafites occurring and bringing home big chunks to toss in come acid in hopes that there were more crystals inside. Occasionally the betafites will pop out whole if you're lucky. My advice if you go is to try to break off big chunks if you can and bust them up. We found crystals up to 2 inches and clusters up to 4 inches, and only spent one day working at it. I'd love to get back there one day and give it another go. And by the way I wold be extremely surprised if it was all mined out. The calcite body is massive, and from what I saw it looks like the betafites go all through it.
[Jay Vonderhey 2009]



Now we need someone to finish the article.



Click here to view Best Minerals B and here for Best Minerals A to Z and here for Fast Navigation of completed Best Minerals articles.

Rock Currier
Crystals not pistols.



Edited 6 time(s). Last edit at 12/28/2012 08:31PM by Rock Currier.
avatar Re: Betafite
November 02, 2009 11:22AM
Photo 255453 ain't no betafite!

Goethite ps after Pyrite. We've discussed this particular piece before, probably should be deleted.

Jolyon
avatar Re: Betafite
November 02, 2009 11:58AM
Well, at least I have deleted it.

Rock Currier
Crystals not pistols.
avatar Re: Betafite
December 27, 2010 02:26AM
This article should probably either be deleted or merged into the pyrochlore article (maybe an article for pyrochlore supergroup as it's pretty much impossible for amateurs to tell the difference between group members).

Jolyon
avatar Re: Betafite
December 27, 2010 05:30AM
Thats a worrying thought Jolyon - if thats the criteria 90% of minerals will need to be lumped with something else!

Regards,
Ralph
avatar Re: Betafite
December 27, 2010 11:08AM
Yes, the article will need to be reworked somehow to take into account the current nomenclature. This article is not really a first draft even and it is not included in the fast navigation list of articles that have their first draft completed. It was only initiated to make a place for some good information about the Silver Crater betafite occurrence and our image gallery has not yet been explored for images of betafites from other localities.Ill mark it as under construction.

Rock Currier
Crystals not pistols.



Edited 1 time(s). Last edit at 12/27/2010 11:12AM by Rock Currier.
avatar Re: Betafite
December 27, 2010 12:55PM
The problem is particularly severe with pyrochlore group minerals in that most 'betafite' specimen photos uploaded to mindat are probably not any type of betafite at all under the new classification, so to have any of these photos under the category of 'betafite' now is misleading.
avatar Re: Betafite
December 27, 2010 07:07PM
Yes, misleading indeed. Did the fellow who did the work on the group ever bother to at least characterize the betafites from Betafo which is the type locality in Madagascar? Unless the betafites from there turn out to be a mixture of minerals like limonite it would seem that there is no way they could justify throwing the name of betafite away as a species as a species.

Rock Currier
Crystals not pistols.
avatar Re: Betafite
December 27, 2010 07:28PM
Essentially, betafite was always defined as Ti > Nb

However, with almost all 'betafite' samples examined as part of the study, Ti is < Nb, meaning it's actually one of the pyrochlore group minerals, with the exception of betafite samples from the moon.

So, it was wrong and needed fixing.

Now we end up with a confusion that the betafite group is now named after a place (betafo) where the mineral probably doesn't even come from. Personally I think that's a bit silly, but that's the way it is.

There are many similar complications, like the type specimen of Rhodizite actually being Londonite, etc...

It comes down to the type definition being more important than the type specimen.

Jolyon
avatar Re: Betafite
December 27, 2010 08:51PM
That defies common sense. So they find this mineral from Betafo and they call it betafite and it has a long history of usage should not the betafite like mineral from the moon be given an new name and not used to redefine the species? Its like using the turquoise from Linch Station Virginia to define turquoise and ignore the material from near Mashad, Iran which has been called turquoise for more than 1000 years and saying that is not turquoise. Such redefinitions are not well thought out. In the case of the Persian turquoise it does appear to be the same as the stuff from Linch Station, but it was not particularly taken into consideration when the structure was done on it.

Rock Currier
Crystals not pistols.
avatar Re: Betafite
December 27, 2010 08:57PM
Personally I think the betafite name should have been killed off completely and replaced with, for example, titanochlore for pyrochlore-like minerals where Ti>Nb

But whether we like it or not, what was known as "betafite" isn't betafite any more, and even if the group names had not changed at all, they would still all have to have been moved to 'pyrochlore'.

Jolyon
Re: Betafite
December 28, 2010 02:46AM
    
The problem is that someone redefined Betafite in such a way that Betafite from the type locality in Madagascar was no longer Betafite! What should have happened is that either the name gets dropped as a species entirely or it is defined according to the type locality material. To reassign the name to something else after having been a species for so long is crazy! And for everyone's information, according to Dana 7th Edition, Betafite from Ambolatara, near Befalo ( the type locality according to Fleischer) contains 18.3% TiO2 and 34.8% Nb2O5. The Betafite from Silver Crater contains 12% and 34% respectively.
avatar Re: Betafite
December 28, 2010 03:20AM
Don't panic. It may not be as bad as it seems.

Here is what the article says about calciobetafite (and betafite):

Hogarth (1977) defined betafite as a uranium-rich Ti-dominant pyrochlore, hence the origin of calciobetafite, a calcium-dominant Ti-rich pyrochlore (Mazzi & Munno 1983).

However, all published analytical data on (non-defect) betafite have Ca in excess of U [except the mineral from the Moon studied by Mokhov et al. (2008) (oxyuranobetafite)];

consequently, by current standards, betafite is defined as a calcium-rich and Ti-dominant pyrochlore. This renders the name calciobetafite redundant, and has the added effect of bringing members of the betafite group in line with the other groups (furthermore, type calciobetafite is Nb-dominant, not Ti-dominant, and belongs to the pyrochlore group).

---

In essence, the 1977 paper defined Betafite as U rich, but excluding calcium. Calciobetafite was defined later, in 1983, as a betafite where U was NOT dominant. Confusing, and not entirely sensible.

The new format kills Calciobetafite.

So.. if you have something with Ti>Nb then yes, it's a betafite group mineral. But which one, it's pretty much impossible to tell. Although there are only two species described in the paper, there are many more possible species.

Jolyon
Re: Betafite
December 28, 2010 03:03PM
    
Hello Jolyon,

I didn't have time to calculate atomic ratios last night but did so now. Unless I made a mistake in my calculations, the "betafite" from the type locality has a Nb:Ti atomic ration of 1.14:1 and the Silver Crater stuff 1.71:1 According to this, the type material was never Betafite to begin with if "betafite was always defined as Ti > Nb". I think it is a lot more complicated than that.
Added note: Had a look at the Handbook of Mineralogy ( should have done that first) and according to that Betafite is defined as U>20% and 2Ti> or = (Nb+Ta). We missed the 2 times. So by that definition both are Betafite according to the old system of classification.



Edited 2 time(s). Last edit at 12/28/2010 03:21PM by Reiner Mielke.
avatar Re: Betafite
December 28, 2010 03:30PM
In the Hogarth 1977 paper, the definition of Betafite is 2Ti > Nb+Ta

Essentially, what he did was to divide the group up unevenly, with any sample containing a minimum of 33% Ti (compared to Nb and/or Ta) being Betafite.

If you look at Figure 1 in his paper, you'll see what he did. This was quite clearly a 'cheat' to get more 'betafite' samples.

The new rule is even more confusing at first!

From Atencio et al (2010) paper:

"The determination of a proper group is made by the dominant valence at B, not by a single, dominant ion. That is, the numbers of all tetravalent cations are summed to give a total number of M4+, the numbers of all pentavalent cations to give a sum M5+, and so on.

For this purpose, a group of atoms with the same valence state are considered to be a single constituent (Hatert & Burke 2008).

If M4+ > M5+ and M4+ > M6+, then the group is: Betafite, if Ti is the dominant M4+ cation.

If M5+ > M4+ and M5+ > M6+, then the group is: Pyrochlore, if Nb is the dominant M5+ cation,Microlite, if Ta is the dominant M5+ cation,Roméite, if Sb is the dominant M5+ cation.

If M6+ > M4+ and M6+ > M5+, then the group is: Elsmoreite, if W is the dominant M6+ cation." - end quote

So not only does Ti have to be dominant in this position, it has to be greater than the sum of both Nb AND Ta, compare Figure 2b in the 2010 paper with Figure 1 in the 1977 paper.

On the positive side, Figure 2b does show a number of genuine betafite compositions, not just the two lunar samples (presumably the two right up near the Ti peak of the pyramid), so maybe there's hope for type locality and canadian betafite after all.

Jolyon



Edited 1 time(s). Last edit at 12/28/2010 03:31PM by Jolyon Ralph.
Re: Betafite
December 28, 2010 04:58PM
    
Here is the problem as I see it. The new classification system depends on knowing where in the atomic structure the ions are, which assumes the mineral in question has an atomic structure ( as per definition of a mineral). The Hogarth system was a classification system based mainly on chemistry in which the atom positions of the ions was not critical. The problem is that the vast majority of radioactive pyrochlores are metamict and have no atomic structure ( strictly speaking they are not minerals). Under the new system these can not be classified. Under Hogarth's system they can. Hogarth also ignored OH which the new system does not and that is a huge problem with the new system. What Hogarth did was accommodate the type locality material so that it would not lose species status because it was in many ways different from the other pyrochlores. I wouldn't call that cheating but being realistic and practical.
I am not willing to accept that my metamict specimens are not minerals and I will continue to use the Hogarth system so that I can name them, end of problem. By the way I also consider Native Mercury to be a mineral and have it in my collection >:D<
avatar Re: Betafite
December 28, 2010 05:12PM
Well, Hogarth was trying to keep betafite as a valid mineral, but some things are not destined to be true mineral species.

Would you want the IMA to "cheat" to allow limonite to be a mineral? I'm sure you could do that too if you ignored OH ;)

Jolyon
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