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Mineralogical ClassificationMetatorbernite

30th Jan 2019 09:47 UTCJolyon Ralph Founder

Why hasn't this been discredited yet as it seems to be simply a dehydrated torbernite (Cf. "Leonhardite" and laumontite)

30th Jan 2019 10:04 UTCErik Vercammen Expert

And there are a lot of meta-uranium bearing minerals!

30th Jan 2019 14:56 UTCUwe Kolitsch Manager

You are comparing apples (structurally and compositionally well-defined hydrates with water molecules in an interlayer space) and oranges (zeolites with continuously variable water contents in large voids).

30th Jan 2019 15:40 UTCRichard Gunter Expert

If the laumontite-leonhardite is a step-wise dehydration rather than a continuously variable water content would it not be closer to the structural water held by the uranium phosphate-arsenate phases?

30th Jan 2019 15:48 UTCUwe Kolitsch Manager

Don't know - I haven't read the relevant literature on leonhardite.

30th Jan 2019 15:52 UTCTom Tucker

The two species, torbernite and metatorbernite, have quite distinctive x-ray patterns, from the data on Mindat.

30th Jan 2019 15:58 UTCRichard Gunter Expert

Hi Tom:

I was wrong about that.

30th Jan 2019 16:23 UTCJolyon Ralph Founder

For the laumontite/leonhardite situation see:

https://link.springer.com/article/10.1007/BF00199498

http://www.iza-online.org/natural/Datasheets/Laumontite/Laumontite.html

30th Jan 2019 17:24 UTCJakub Plasil Expert

Moreover, under certain conditions metatorbernite and metazeunerite form instead of higher hydrates!!!

30th Jan 2019 17:34 UTCRichard Gunter Expert

Hi Jakub:

My thought on the non-dehydrating laumontite from the Dankoe Mine was that it formed as a stable phase very much like metatorbernite. Kiseleva et al. (1996, Am. Min.) has a three stage dehydration for laumontite and calls them laumontite-leonhardite-metaleonhardite. It seems laumontite does not dehydrate like the other zeolites.

30th Jan 2019 22:16 UTCRalph S Bottrill 🌟 Manager

The dehydration of laumontite greatly affects the unit cell parameters but not the overall topology of the structure, or it’s symmetry. All the same, it’s analogous to other chemical solid solution series, eg Albite-anorthite, except we are just dealing with molecular water, not anions or cations.

30th Jan 2019 22:44 UTCRichard Gunter Expert

Hi Ralph:

If the dehydration of laumontite affects the unit cell parameters then it should be somewhat similar to the torbernite-metatorbernite dehydration rather than the "normal" zeolite dehydration that does not affect the silicate structure. It also seems from my reading that laumontite does not have exchangeable cations. Are we looking at a structure that is part way between a zeolite and a sheet silicate?

31st Jan 2019 16:10 UTCUwe Kolitsch Manager

Dehydration of zeolites always affects the unit-cell parameters.

31st Jan 2019 16:42 UTCKevin Conroy Manager

Could argentite be thrown into the mix? I don't think that anyone has one in their collection!

31st Jan 2019 17:09 UTCRichard Gunter Expert

Hi Uwe:

I guess I need to do a bit more reading on the subject as I thought dehydration of zeolites was a reversible process that did not affect the "skeleton" of the zeolite phase.

31st Jan 2019 17:19 UTCUwe Kolitsch Manager

The skeleton distorts during the dehydration.

31st Jan 2019 17:40 UTCJolyon Ralph Founder

But the interesting thing is that the 'leonhardite' phase is one that cannot be further dehydrated nor can it be rehydrated to laumontite. Which to me makes me think it's something different

31st Jan 2019 17:46 UTCUwe Kolitsch Manager

I agree, leonhardite seems to be a special case.

Some zeolite topologies can be fully de- and rehydrated, others collapse and become X-ray amorphous.

31st Jan 2019 17:48 UTCRichard Gunter Expert

Hi Jolyon:

I was thinking the same thing. Check out the Kiseleva article and see how they classify the laumontite-leonhardite-metaleonhardite series. With advances in the measurements of these phases it might be that laumontite-leonhardite is part of a non-zeolite group sequence based on the non-reversibility of the dehydration. Certainly food for thought.

31st Jan 2019 19:42 UTCRichard Gunter Expert

Just to complicate things a little further, Fridriksson et al. (2003, Am. Min.) did a study where they identified two water sites in laumontite; one has zeolitic water and one does not. So partial dehydration on the zeolitic water site is possible but not full dehydration.

31st Jan 2019 20:42 UTCRalph S Bottrill 🌟 Manager

We are pretty inconsistent in mineral classification. With tourmalines, amphiboles etc we remove a proton or two and it’s a new species, or replace an alkali with hydronium in some groups, etc, but we lose a huge amount of water in laumontite, collapsing the structure, but still consider it’s the same species?

31st Jan 2019 20:58 UTCRichard Gunter Expert

Hi Ralph:

Would it not be more consistent to re-introduce leonhardite (or some other species name) for the laumontite that has lost its zeolitic water but retained its non-zeolite water? Fridriksson also indicated there are variable occupancies in both water sites. Isn't nature grand!

31st Jan 2019 21:12 UTCJolyon Ralph Founder

I'm glad I don't have to sort out the mess of the questions I ask :)

31st Jan 2019 22:21 UTCRichard Gunter Expert

Asking such questions points out the inconsistency and "work-in-progress" nature of this science. Laumontite has been described since the 18th Century but it is still is not finished.

1st Feb 2019 01:14 UTCKeith Compton 🌟 Manager

Richard

When the laumontite finally dries out in another 100 years or so, or turns to dust, they may have an answer !! ((-:) .. but I have certainly had some laumontite form the south coast (NSW) that had/have turned to dust and I still don't know.... oh well.

At least the discussion of laumontite/leonhardite gives future mineralogists something to work on and ultimately rename, in addition to perhaps finalising the tourmaline and amphibole groups this century, but I wouldn't bet on that either .

Think I'm still heat affected at the moment and getting dehydrated in the heat - maybe I should add some water or alcohol to the mix !!

1st Feb 2019 03:18 UTCFrank K. Mazdab 🌟 Manager

Yo Keith... you really are not a fan of vanadio-oxy-chromium-dravite, huh? :-)

1st Feb 2019 15:28 UTCRichard Gunter Expert

Hi Keith:

If you are heat affected and dry you should come to the Fraser Valley in British Columbia. You will not dry out in the winter here.

I am also not a fan of what the Tourmaline Group has become, especially since fairly sophisticated instruments are necessary to determine what an individual sample actually is.

1st Feb 2019 21:05 UTCRalph S Bottrill 🌟 Manager

Richard, I agree it seems sensible to reinstate Leonhardite as it can be differentiated chemically and structurally from laumontite, and collectors can easily recognise it as the powdery material where their laumontite used to be!

1st Feb 2019 21:06 UTCRalph S Bottrill 🌟 Manager

Keep hydrated Keith, break out another bottle!

1st Feb 2019 22:16 UTCRichard Gunter Expert

Hi Ralph:

I agree about leonhardite, the two water sites should have sealed it but Fridriksson et al. (2003) never followed up, as far as I can find.

I am still not sure about the Dankoe Mine samples that give a laumontite XRD trace but do not dehydrate. Use of another measuring device (Raman?) might help locate the water sites in it. It might be a "primary leonhardite" which has been identified previously. I have a sample and can provide small crystals.

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