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Chrysocolla : Cu2-xAlx(H2-xSi2O5)(OH)4·nH2O

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minID: YE5-P0D

Chrysocolla : Cu2-xAlx(H2-xSi2O5)(OH)4·nH2O

This image is copyrighted. Unauthorized reproduction prohibited.
Field of View: 3.8 mm

Fe-rich, analysed (EPMA + IR + Raman) chrysocolla. Collection and photo Giorgio Bortolozzi.

The simplified formula (O = 9), based on EPMA results, is [Cu1.06,Fe0.94](Si2O5)(OH)4·nH2O, i.e. a Cu-dominant composition. The Raman and IR spectra are very similar to that of "chrysocolla" reported in the literature.

This material was described in:
Bortolozzi G., Ciriotti M.E., Bittarello E., Moeckel S. (2015): Monte Avanza, Forni Avoltri; Carnia (Udine, Friuli-Venezia Giulia): conferme e nuovi ritrovamenti. Micro, 1-2015, 2-39.

This Photo was Mindat.org Photo of the Day - 12th Jan 2016

This photo has been shown 1466 times
Photo added:22nd Apr 2015
Dimensions:644x555px (0.36 megapixels)
Date/Time of Photo:1st Sep 2014 16:26:49
Camera:NIKON COOLPIX S30
Software:Adobe Photoshop 7.0
Exposure time:1/80s
Aperture:f/5.9
Focal Length:22mm
Focal Length (35mm film equivalent):157mm
ISO speed:80
View Giorgio Bortolozzi's Photos View Chrysocolla Gallery

Discuss this Photo

PhotosChrysocolla - Monte Avanza Mine, Forni Avoltri, Udine Province, Friuli-Venezia Giulia, Italy

15th May 2015 17:26 BSTRob Woodside Manager

Here is a published yellow Chrysocolla that has been identified by IR , Raman and EMPA. However in the article (in Italian) says this about the chrysocolla (Google translation);


"Chrysocolla ( chrysocolla )

Contrary to expectations , the silicate

already reported ( Cecchi , 1986) , but not confirmed

by analytical investigations , it is enough

rare in Monte Avanza . Accompanies species

secondary present and it is in the masses

criptocrystalline and scabs opaline color from

green to blue or unusually pale ,"


It is very surprising that no mention of the analysed yellow Chrysocolla occurs in the chrysocolla description that gives the expected colours. Since this is an analysed and published specimen, the gold standard for photo approval, I felt I had no choice to approve this photo. Here is the correspondence on this:


> Ref: http://www.mindat.org/picshow.php?id=679597

>

> Thank you for uploading this photograph to mindat.org - as part of the

> review process for photo submissions our editors have raised the

> following issue(s) with this photograph that prevent us from approving

> it:

>

> * Your photo might not be the minerals you said it is

>

> Hi Giorgio,

> How was this analysed??

> Cheers,

> Rob woodside


EPMA + IR + RAMAN at Torino University (Bittarello E:).

You can see the photo in my recent article in Micro, that I enclose for you.

Regards.

Giorgio


Hi Giorgio,

That looks like a very interesting paper. Where was it published? I hope you

added it to the references for that locality.


When posting material that's been analysed please give the methods and

analyst as you did in the reply. (EPMA + IR + RAMAN at Torino University

(Bittarello E:).)


However yellow chrysocolla??? There is some problem here. If you are sure

there is no mix up here, I'll approve it and start a talk page about it.

Yellow chrysocolla....

Cheers,

Rob


Hi Rob,

the article was recently publied in Micro I/2015 (look the enclosed), that I mentioned in Mindat.

Erica Bittarello is one of analysts and co-authors.

Kind regards.


Giorgio


I tried to attach a copy of the publication (5 MB) but have been defeated by the size limitation (1 MB).


What to do? Has anyone ever seen a yellow Chrysocolla?

;

15th May 2015 20:07 BSTRock Currier Expert

I would email the author and attach the image of the yellow chrysocolla and say something like "really?" Since the color flies in the face of currently accepted wisdom it would think it might be nice to a confirming analysis. I would ask if a sample of this yellow stuff could be sent to say Bob Downs at the U or A. I think it might be worth his attention since there is so much chrysocolla found in Arizona.

15th May 2015 22:04 BSTRob Woodside Manager

I tried this as you can see in the correspondence above and he is sure there is no mix up and the analysis (EMPA, IR, Raman by E. Bittarello at Torino U.) proves yellow chrysocolla. Oddly the paper makes no comment about the yellow and says the rare chrysocolla there is green to blue as one would expect.

16th May 2015 06:45 BSTRock Currier Expert

If a blue blue/green color is not intrinsic to chrysocolla then we probably don't understand what is going on and I think that someone is going to need to study it to find out what is going on and why it can be yellow. Do you know if George Rossman is aware of the paper and this yellow chrysocolla?

17th May 2015 10:24 BSTMarco E. Ciriotti Manager

The translation made by Google is not very correct. The correct is as follow:


"Chrysocolla (chrysocolla)

Contrary to expectations, the silicate already reported (Cecchi , 1986), but not confirmed by analytical investigations, it is enough rare at Monte Avanza. It accompanies the secondary species which occur in the deposit and it is in cryptocrystalline opaline masses with colour that varies from green to blue or unusually yellowish".


Ref:

Giorgio M. Bortolozzi, Marco E. Ciriotti, Erica Bittarello, Steffen Möckel (2015): Monte Avanza, Forni Avoltri, Carnia (Udine, Friuli Venezia Giulia): conferme e nuovi ritrovamenti. Micro, 13, 2-39.



Here is my comment:

The yellowish colour of some very rare samples of "chrysocolla" found in a limonitic environment is probably due to the presence of Fe.

A stechiometric simplified formula (O = 9), based on EPMA results, could be represented as [Cu1.06,Fe0.94](Si2O5)(OH)4·nH2O.

The Raman and IR spectra are very similar to that of "chrysocolla" which we can find in literature.

In my opinion "chrysocolla" is not a valid mineral species but a mixture of chalcedonic quartz and other phases.

Most probably the yellowish phase, described as chrysocolla in the above mentioned paper concerning Monte Avanza, is a mixture of Cu, Fe and Si phases.

Strangely chemical stechiometry and spectroscopies are compatible with that of "chrysocolla" which we can find in literature.

12th Jan 2016 07:36 GMTChristian Auer Expert

Ok chrysocolla has the formula Cu2-xAlx(H2-xSi2O5)(OH)4 · nH2O at least here on mindat.

This species on the picture has [Cu1.06,Fe0.94](Si2O5)(OH)4·nH2O.


Chrysocolla has a valid status - also at least here on mindat.

Strangely Raman and IR spectra from this yellow phase gave similiar results as chrysocolla.

Still with that chemichal formula it isn`t chrysocolla and shouldn`t be mentioned.

Marco probably knows the locality better and a mix of Cu-Fe-Si phases as he suggested sounds fine.


Wonder why this picture was picked out as POTD unless you want to start a discussion about analytic methods ...

12th Jan 2016 08:16 GMTAlfredo Petrov Manager

I suppose, as one of my professors used to say, " Color is the least reliable property for mineral identification"... but nevertheless the one every collector uses the most.

12th Jan 2016 09:15 GMTHerwig Pelckmans Expert

I can only agree with Christian.


Since when is the chemical composition of a mineral sample less important than its "very similar Raman and IR spectra" when it comes to identifying the mineral?

The chemical formula for chrysocolla, as mentioned on Mindat, does not mention any Fe substitution, only Al.

The analysis of the sample indicates no Al, and almost equal quantities of Cu and Fe ...

Does not sound like a match to me.


Cheers, Herwig

12th Jan 2016 10:18 GMTUwe Kolitsch Manager

Have added the following info to the photo:


The simplified formula (O = 9), based on EPMA results, is [Cu1.06,Fe0.94](Si2O5)(OH)4·nH2O, i.e. a Cu-dominant composition. The Raman and IR spectra are very similar to that of "chrysocolla" reported in the literature.


This material was described in:

Bortolozzi G., Ciriotti M.E., Bittarello E., Moeckel S. (2015): Monte Avanza, Forni Avoltri; Carnia (Udine, Friuli-Venezia Giulia): conferme e nuovi ritrovamenti. Micro, 1-2015, 2-39.


I disagree with Christian and Herwig - the Cu-dominance is the important point here. Al content is not necessary since it can be zero.

Additional PXRD data would be nice, though.Theoretically, the Cu (divalent) and the Fe (most probably trivalent) might be ordered in the structure.


BTW, for a previous discussion see http://www.mindat.org/forum.php?read,11,370292,page=1.
 
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