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Olmiite versus Poldervaartite

Posted by Mario Pauwels  
Mario Pauwels August 02, 2008 10:48AM
Hi all,

I was looking thru the Poldervaartite gallery and I think there are some Olmiite specimens between the Poldervaartites.

Both pictures: 110387 & 8817 are probable Olmiite instead of Poldervaartite.
One picture: 122293 should be changed in Olmiite / Poldervaartite / Calcite.

Some other Poldervaartite pictures look also a bit "suspicious", but they are more difficult to examine on the pictures.

Mario Pauwels
James Spann August 02, 2008 02:07PM
I had been collecting quite a few Poldervaartite specimens and loved the variety you could choose from.
Now I have to go back and take a guess at what is what as I have them in all different spectrums of colour from chalky white to deep russet red.
After learning to spell and say Poldervaartite, it isn't half as much fun to say Olmiite. (:P)

Gail Patricia Copus Spann
Anatoly Kasatkin August 07, 2008 07:55PM
For your information I can tell you that during last year we microprobed more than
15 specimens from N'Chwaning II and Wessels and ALL of them independently
of habit, colour etc. - all turned out to be olmiites with very clear dominance of Mn over Ca in the second position.
Now I have a strong suggestion that all the poldervaartites that filled the mineral market (including all pictured on mindat) are in fact olmiites.
It needs to be said that even the analysis given by the authors of poldervaartite for the homogenous grain of holotype material showed dominance of Mn over Ca.
Only one crystal of holotype poldervaartite used to make a crystal structure showed,
according to authors, slight dominance of Ca over Mn. So actually it seems that
even the holotype poldervaartite is, in fact, the zonal growths of poldervaartite/olmiite.
In our analyses we unfortunately never found traces of such zonal growths, never even a ratio
close to 50/50, everytime Mn was strongly dominant. One thing is evident: it is impossible to clearly ID the species basing on visual examination.
I discussed this problem several times with Renato Pagano (co-author of Olmiite), also with Dr.Bruce Cairncross etc. Renato said that more investigations are needed.
So far, I suggest poldervaartite being EXTREMELY rare species. I certainly don't have it in my systematic collection. Since SA mines are very prolific we can only hope that new find of Ca-rich material will be made, but so far, very tough WDS-work and very BIG luck are necessary to find points of the true poldervaartite!

Uwe Kolitsch August 07, 2008 08:34PM
Thanks Anatoly, for this interesting information. I have updated the mineral files.
Franz Neuhold September 23, 2008 10:18AM

I recently had a visibly heavily zoned crystal of Olmiite-Poldervaartite (N'Chwaning II) under the SEM. The EDS results were ranging from a - most likely - typical Olmiite (CaO:MnO 1,35) to nearly Mn-free Poldervaartite (CaO:MnO 200!) in the outer rims. The crystal faces and fractured areas are both free of any overgrowths.

But as Anatoly already said: naming it Olmiite or Poldervaartite should not be done basing on visual examination!

James Spann September 23, 2008 12:07PM
Check out the whole new article in Mineralogical Record, we got ours yesterday. It gets into the whole "what's what" aspect.

Gail Patricia Copus Spann
Jolyon & Katya Ralph September 23, 2008 12:13PM
I've added a new entry:

Perhaps we should move all Olmeiite/Poldervaartite photos to this unless they've been confirmed by EDS or similar.

Peter Hargis February 26, 2009 02:46PM
I'm just catching up on this forum post. I'm looking at what I think is Poldervaartite...but now I'm not sure. It's listed as Poldervaartite w/ Bultfonteinite. I don't have any equipment except my eyes. Can anyone help me ID it? Thanks.
open | download - poldervaartite.jpg (37.1 KB)
Marco E. Ciriotti February 26, 2009 03:51PM
I agree with Anatoly and other replies. In our work "Italian Type Minerals" as note we marked:

Olmiite is the Mn-dominant analogue of poldervaartite, Ca(Ca,Mn)(SiO3OH)(OH), with which it forms a
series. A fair amount of “poldervaartite” have reached the market in the recent years, but most samples turned
out to be olmiite. Genuine poldervaartite specimens, thus, must be regarded as extremely rare and seem
to be limited to the original finding in the 1980s at the Wessels mine, Cape Province, Republic of South
Anatoly Kasatkin February 26, 2009 05:10PM
Since my last post here I visited Bill Pinch to see his wonderful collection and he let me remove a small cluster from his incredible miniature sample of what was labelled as "Poldervaartite" from Wessels mine and, according to Bill words, was fully studied (XRD, probed, Raman). The fact that attracted my attention was that his sample was absolutely different from hundreds of "Poldervaartites" (and in reality Olmiites) I have seen and we studied before. Crystals on Bill's sample were prismatic and almost totally colorless and transparent. When I returned to Moscow we made independent microprobe analysis and infrared spectrum. Well, it was almost pure end-member Poldervaartite! So I can say now that Poldervaartite exists not only in Ca-dominant zones or points in polished sections. It exists in wonderful crystals! I will try to find time to put a photo on Mindat. But it's true also that I never saw a second sample even close to that in Bill's collection.
Also I can note that in Franz Neuhold's case it can be probably a first reliable find of Poldervaartite from N'Chwaning II.

Mario Pauwels April 03, 2009 10:44PM

What is happening with the Poldervaartite gallery now ?

It turned out that all recently discovered Poldervaartites are in fact Olmiites, but many of these new specimens are still posted and displayed with picture in the Poldervaartite gallery.

Mario Pauwels
Pierre Rondelez November 29, 2012 06:41PM
Yes indeed Mario,

More than3 years later and not much has changed on Mindat concerning Poldervaartite/Olmiite.........
Strange to say the least.
Branko Rieck November 29, 2012 07:59PM

there are currently 9 photos in the poldervaartite gallery and 308 in the olmiite gallery. So I cannot really consent with your statement of " not much has changed". However I agree that some of the 9 poldervaartite photos might not be what they claim to be.

Pierre Rondelez November 30, 2012 08:07AM

Yesterday morning, there were 13 poldervaartites in the gallery, by evening 8 remained, the rest had been removed to the olmiite gallery.
So yes, some changes were made yesterday...........
Most of the ones remaining will remain there I am afraid, just look at who posted them on the claim that they came from old collections, which really means nothing else than before the existence of olmiite (and the wrong id. of poldervaartite) was known.
Mario Pauwels November 30, 2012 10:26AM
Hi Pierre and all others,

Since I started this tread more then four years ago, a lot of the mislabeled "Poldervaartite's" are moved to the Olmiite gallery. This was a very slow proces, and during these four years there were still new Olmiite's pictures posted (and accepted !) in the Poldervaartite gallery, while it was clear since Anatoly's statement that it was wrong to accept them as Poldervaartite.

Finaly everything looks solved now after your recent complains Pierre(tu). So thanks for bringing this topic back under attention.
I also agree with you that from the 7 pictures who remain at this moment in the Poldervaartite, that most specimens look very suspicious and are most likely Olmiites.

Best regards,
Mario Pauwels
Pierre Rondelez November 30, 2012 10:52AM
Yes Mario and all others,

Things seem to be moving now (at last), only 7 remaining today of which 2 are probables, the other 5 (amongst which the head photo) are very suspicious.

Branko Rieck November 30, 2012 11:19AM

From my experiences there are 2 "most likely", one is confirmed and 4 doubtful. Please be patient for just some more hours, and we will have a solution. I am working on it.

Branko Rieck November 30, 2012 04:29PM
@ all

There are currently 3 specimens remaining in the poldervaartite photo gallery which are considered true IDs. I hope that no other, incorrectly identified photos are uploaded in the future, but if one slips through there is always the possibility of a note in this thread.

@Matio, Pierre

Thanks for bringing this up!
Pierre Rondelez November 30, 2012 05:25PM
OK Branko,

Thanks for the good work,

Mario Pauwels December 01, 2012 09:47AM
I was just wondered why it has taken more than four years to cleaning this mess up. I truly can not believe that a dealer could have that much influence to keep misidentified specimens in a certain gallery, or that I was not taking to seriously when I started this Olmiite versus Poldervaartite topic four years ago...

Anyway I am glad that everything is finally solved now. Thank you everyone for your response and also Branco for your 'action'.

Best regards,
Mario Pauwels
Pierre Rondelez December 01, 2012 10:10AM

I could not agree more.


Mario Pauwels Wrote:
> I was just wondered why it has taken more than
> four years to cleaning this mess up. I truly can
> not believe that a dealer could have that much
> influence to keep misidentified specimens in a
> certain gallery,
or that I was not taking to
> seriously when I started this Olmiite versus
> Poldervaartite topic four years ago...
> Anyway I am glad that everything is finally solved
> now. Thank you everyone for your response and also
> Branco for your 'action'.
> Best regards,
> Mario Pauwels
Reiner Mielke December 01, 2012 12:55PM It seems that the N'Chwaning I Mine mine didn't produce any olmiite only poldervaartite, at least according to Mindat? Is that an error?
Pierre Rondelez December 01, 2012 01:58PM
Hi Reiner,

That must surely be an error!

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