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Improving Mindat.orgCousinite

18th Feb 2019 16:28 UTCLuc Vandenberghe Expert

Hi All,

About this photograph, https://www.mindat.org/photo-800770.html , and many others on the web, I wonder how it was possible to put a name on the photographed mineral species ,,,

The mineral cousinite species was summarily described by J. F. Vaes: Cousiniet, een nieuw uraanmineraal. Geology in Mijnbouw 20, 449-449 (http://rruff.info/rruff_1.0/uploads/GM20_449.pdf)

The IMA does not recognize the species as the data is poorly documented (http://rruff.info/rruff_1.0/uploads/AM44_906.pdf)

The holotype or other study materials have disappeared,

In 1975, Dr. Michel Deliens published a work on uranium molybdates of Shinkolobwe in which he states "Let us also note that J.F. Vaes (1958) provided fragmentary data on a molybdate of uranium and magnesium. of Shinkolobwe likely to be identical to our mineral ",

(Https://popups.uliege.be/0037-9395/index.php?id=4906&file=1&pid=4905)

How is it possible to name a mineral species in the absence of holotype or materials used for the first study, in the absence of physical and crystallographic data ???

Apart from J.F. Vaes nobody has actually seen this mineral species.

In addition

In illo tempore I asked to add the following remark on the page of the cousinite: "Davison (1954) also describes a molybdate of Mg as monoclinic / pseudo-orthorombic with a = 6.37, b = 33.46, c = 15.0 A and beta = 90 °. This mineral is listed in the recent compilation of unnamed species (Smith & Nickel, 2007) as UM1954 - // - MoO-MgU

This was a mistake because, after finding the work of Davidson, it appears that the author only mentions a molybdate of uranium.

It was not until 1958 that C. Guillemin described a molybdate of uranium and magnesium with the characteristics listed above.

In my opinion, the reference to Davidson should be removed and replaced by that of C. Guillemin, copy of which is attached.

Greetings from Belgium

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20th Feb 2019 19:53 UTCRalph S Bottrill 🌟 Manager

Agreed. Message sent.

It looks a bit like molybdenite, and most molybdates are brightly coloured, but Mindat lacks any physical descriptive data.

It’s described as “Possibly a "Mg-Umohoite"”, though the latter lacks cations Mg could substitute for.

Umohoite itself is described as black to green, but most of its photos are bright red to orange so that deserves an explanation also.

20th Feb 2019 22:38 UTCTravis Olds Expert

Very dark umohoite can have a metallic luster, but agree that it shouldn't be called cousinite. Was it tested at all? I'd like to if not, Brent.

I had wondered if the color differences of umohoite were related to U valence differences, but haven't tested it.. The color change seems to be (in part) related to differences in chemistry. Samples from Rabejac have appreciable Cu up to ~2.7 wt% ox:

https://www.mdpi.com/2075-163X/8/9/414

According to Belova, orange-red and yellow umohoite has higher Fe (+/- Ca?) content, and black has low Fe. I'm not sure why Cu and Fe substitution would produce the same orange-red coloration if it wasn't tied to slight U valence changes..

https://inis.iaea.org/search/search.aspx?orig_q=RN:18072751

20th Feb 2019 22:49 UTCBrent Thorne Expert

The specimen has not been tested by me. The only information that I have on the specimen, I included in the description.

Travis, if you want to analyze it, I would be happy to send it to you.

Brent

21st Feb 2019 08:49 UTCLuc Vandenberghe Expert

Analyzed on what basis to find cousinite ???

The only information on this questionable "species" is in links in my text.

There is only a chemical analysis and no physical data ....

At best an analysis can give only one result, already mentioned by M. Deliens, a Mg-umohite

In Shinkolobwe, the crystals of umohoites are in flattened tablets constituing fasciculate associations.

The colors are :

Black to dark green blue for the Mg & Ni-Ca umohoites;

Yellowish green to bronze yellow for the Ni-umohites.

More informations reading the following works (sorry, in french) :

https://popups.uliege.be/0037-9395/index.php?id=5360&file=1&pid=5359

https://popups.uliege.be/0037-9395/index.php?id=4575&file=1&pid=4574

Cheers.

Luc

21st Feb 2019 17:21 UTCTravis Olds Expert

Brent, yes please! I'd like to take a look.

Luc, I think Brent's sample might be Mg-bearing umohoite like you say and will test by microprobe. Those are useful links. I am just interested in the color differences tested by UV-vis for charge transfer bands + supporting photoemission spectra. Already have green/black/yellow Khazak material from Pavel and green/yellow bronze from Rabejac from Jakub. By chance do you have any extra Shinko dark/Ni-umohoites you'd be willing to trade? It would complete my search.

21st Feb 2019 21:01 UTCRalph S Bottrill 🌟 Manager

If possible some XRD work would be great also! But you may not have enough sample.

21st Feb 2019 21:14 UTCJeff Weissman Expert

I have this image of cousinite, made from a specimen owned by Excalibur Mineral Company, locality is the type locality of Shinkolobwe Mine (Kasolo Mine), Shinkolobwe, Kambove District, Haut-Katanga, DR Congo. Visually matches the Handbook of Mineralogy description of "thin blades, lamellar" and "black, vitreous". Beyond this, nothing more to add. Photograph was made back in the middle 1990's, so no idea where the specimen is now. Looks greenish-black, but I cannot guarantee that the color balance is correct.

21st Feb 2019 22:37 UTCTravis Olds Expert

That reminds me of wyartite, but I've not seen enough of either of these species to judge. Maybe Tony knows where it ended up?

There is plenty for SCXRD for most varieties, except the Rabejac red spheres. I've not found large enough crystals and they probably don't exist. The reported symmetry/cell differences for each variety from Luc's links are interesting. Am still translating but would be good to know why Piret thinks that happens, and if there are actually umohoite-(Mg/Fe/Cu/Ni +/- Ca) members, though maybe their content is always too low to consider it.

22nd Feb 2019 12:57 UTCLuc Vandenberghe Expert

Jeff,

I believe It's necessary to refer to my remarks.

Travis,

I have three samples of umohoite coming from Shinkolobwe.

The three samples show crystals that coud be used for study.

I can send you crytals that I will take from myself or send you the three samples.

However they are not for sale or intended for exchange and samples should be returned.

I do not pay my attention to my mailbox on Mindat...

Thank you to contact me via this address : luc.vandenberghe(at)hotmail.com.

22nd Feb 2019 19:59 UTCTravis Olds Expert

Luc,

That's wonderful :D, I am happy to return anything you are willing to send. I do not need many crystals, and we can continue the exchange over email.

The Mg content recalculates to what might be considered "umohoite-(Mg)" from the original cousinite description data, but just barely based on the dominant constituent rule. If Vaes missed Ca or Fe it would be > 0.5 apfu. Regardless, there could be precedence for a unique and dominantly occupied cation position if a structure can be found.. Assuming extra cations populate a single site in the interlayer and not the U-moly sheet, and ignoring different polytypes or the reason for charge balance (U5+/Mo5+?), the corresponding substitution site in umohoite sensu strico could be either a water molecule or empty space. I don't think you would ever consider a displaced water molecule a "vacancy," especially in a variably hydrated phase, so then perhaps any reasonably populated Mg/Fe site with a defined coordination could do?? E.g. 0.20 Mg:1U pfu?

Too many assumptions yet, but all other given analyses for Ni/Cu/Fe umohoite varieties, including Piret's analysis with 1% MgO, reach no more than ~0.1-0.3 apfu. So if ever some material with sufficient cation content (however that should be defined) is found that has the structure of an umohoite then perhaps it could be an easy description.. On the other hand there will likely be no way to discredit cousinite without the type material, and it would be in a type of limbo like bijvoetite-Y. But really there would be no point. Cousinite hasn't been used for 60 years if you consider when it was grandfathered, and since the Mg-bearing umohoite of Piret is unnamed and there is no hard requirement to name it umohoite-(Mg), it could be appropriate to reapply the name cousinite to that material.

23rd Feb 2019 09:10 UTCLuc Vandenberghe Expert

Travis,

Unless I'm mistaken, the name "cousinite" has never been approved by the IMA. I don't know the reason for its reappearance with the "questionable" status.

In addition, the IMA, in its list of mineral species mentions the work of Michel Deliens (1975) in parallel with that of J.F. Vaes ...

I believe that there is a link between the subject of these exchanges and the name UM1954 - // - MoO: MgU of the list of invalid unnamed minerals (published by the IMA in 2012).

I look forward to hearing from you about umohoites

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