FMF - Friends of Minerals Forum, discussion and message board

[Jan Erik]

During the Mindat conference, and our visit to the mine Taouz, there have been found some new Vanadinites that some of us might believed could be Mimetite. Thats because of the very yellow colour and the fact that there have been found Mimetite before from the area.

One of the found specimen is now analyzed and it showed up to be plain Vanadinite.

In fact. Some of the specimens are very nice, with well defined crystals with a great yellow colour.

[Tomasz Praszkier]

Erik,
did you analyzed it? XRD or which method?
I still didn't analyzed mines, will do that in next weeks.
Tomek

[Jordi Fabre]

Correct, in fact some more specimens were analyzed and all them were Vanadinite, so although the Mimetite exist in Taouz, the specimens recently mined there seems to be just Vanadinite.

[Jan Erik]

Hello Tom

I have not analyzed it, but Jordi have. I have got the result from the analyze from him. I tried to put it with the picture in my posting but did not succeed. I have asked Jordi to post it.

In the meantime I will send you the result Tom.

[Jordi Fabre]

[Tomasz Praszkier]

Erik and Jordi,
this is what I was suspecting. Everyone was excited about new "mimetites" but I was skeptic about this.
I have a few pieces which I will analyze anyway. BTW - which part of the crystals did you analyzed? Some of them have clearly visible difference of color and transparency between core and external part.
Attached is photo of one of the specimens found 6 months ago.

[Jordi Fabre]

[Pete Modreski]

This goes to show, that the common presumption that many of us tend to make, that material in hexagonal prisms is vanadinite, and rounded or botryoidal material is mimetite, is not necessarily always correct!
But, to just add a note of caution to the interpretation of the energy-dispersive X-ray spectrum on which this identification is based, from some years of experience in working with this type of data, it is notoriously difficult to recognize the X-ray emission peaks of As in the presence of Pb. The strongest X-ray peak of As, the As-K-alpha peak, is basically coincident with, and hidden by, the strong L-alpha peak of Pb; about 10.54 keV vs. 10.55 keV. To ascertain whether As is present one has to look for the much lower-energy L-alpha line of As, at about 1.28 keV, which is not excited or detected as efficiently in most EDX systems. Thus, it is easy to not recognize it if some amount of As is really present. It may not be as clear cut as it seems, to conclude that the X-ray spectrum shown here for the Taouz material is necessarily of As-free vanadinite. It really helps to compare a spectrum, obtained with the same instrument, of a known specimen of mimetite or of intermediate vanadinite-mimetite (e.g., "endlichite"), to get an idea of how readily the As X-ray peaks are discernable.

[Jordi Fabre]

Thanks for the infos Pete. I copied below the answer of the analyzer of these Vanadinites:

Relatively recent advances in EDS spectroscopy both in qualitative and quantitative mode have improved the spectral resolution and, specially, the sensibility in the low energy region like the As L-region. Following our expertise (we published 4 new arsenate minerals), in our INCA EDS spectrometer the detection limit of As in routine, qualitative analysis may be less than 1%. So, the spectrum indicated that the sample do not contained significant As for considering an intermediate “endlichite” specimen. In addition, the profile (high) of Pb L-alpha peak as compared with the Pb L-beta peak also indicated that the potential As-content was not significant for “labeling” purposes.
A Pb-arsenate spectrum (duftite) obtained in the same day and in identical analytical conditions is attached. The As L-peak appears with very high intensity and the Pb L-alpha peak appears very enhanced with respect the Pb L-beta peak. On the other hand, our analytical software also permits the As-analysis using the As K-peaks in presence of Pb.

Cheers

[Pete Modreski]

Very good, thank you for showing the additional data and explanation, and I agree, with the improved instrumentation compared to the older equipment that I once used, it's clear that there isn't any significant As in the Taouz sample. Viva la vanadinite!

[Malcolm Southwood]

Thanks, everybody, for clearing this one up. However, I returned from the recent Mindat trip with yet another habit of Taouz "vanadinite", which I wonder if anyone is yet able to verify as vanadinite rather than mimetite. The pale yellow, transparent quality of these crystals reminds me of the famous "gem pocket" mimetites from Tsumeb, although please note the scale; these crystals are less than 0.5mm.

Any thoughts gratefully appreciated
mal

[Jordi Fabre]

I have not analysis of it Malcolm, but it looks to me very similar to some other Vanadinites (analyzed) from Taouz, so if you want my opinion (without analysis ;-) I would say Vanadinite.

[Malcolm Southwood]

Thanks Jordi,
I would certainly not be surprised if that is the case.
mal

[Colleen Thomson]

Thanks for these postings. i too found yellow crystals from here that i was only half convinced were Vanadinite - so thanks for the confirmation!
BTW Mal -those little gemmy crystals are lovely!

[Tomasz Praszkier]

I just received results of "mimetite" analyses. One was yellow one, another melted, orangish - both are just vanadinite as suspected.

Tomek