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Ajoite From Messina
  
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Roger Warin




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PostPosted: Aug 27, 2021 13:39    Post subject: Ajoite From Messina  

Hello,
I have a question: is there a solid solution of ajoite?
FOV : Quartz crystal width = 55 mm.
In my photo, we see the ajoite fibers discolouring, as if there was a loss of copper.

K3Cu2+20Al3Si29O76(OH)16 · 8H2O
Triclinic 1 or -1 ? No wonder with such a formula.
Thank you.



Ajoite_20149_R.jpg
 Mineral: Ajoite
 Locality:
Messina Mine, Musina (Messina), Vhembe District, Limpopo Province, South Africa
 Dimensions: width 55 mm
 Description:
 Viewed:  1875 Time(s)

Ajoite_20149_R.jpg


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Peter Megaw
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PostPosted: Aug 27, 2021 16:56    Post subject: Re: Ajoite From Messina  

Roger, Ajoite is famous for "deteriorating" into chrysocolla, so my first guess would be that that's what you're seeing rather than a compositional shift within an ajoite-XXX series. (yes, I realize changing to chrysocolla is a compositional shift). As I remember, historically there were questions about ajoite even being a valid species because it was so hard to get a decent pattern off of things identified as ajoite. This deterioration was well developed in the recent finds of ajoite from Rancho Jacalito, Sonora, Mexico...only a small percentage of what got analyzed was still ajoite.
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Roger Warin




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PostPosted: Aug 27, 2021 21:29    Post subject: Re: Ajoite From Messina  

Thank you very much Peter,
The chemical formula makes me uncomfortable (I'm just a chemist).
Another fact surprises me in my photo, it is the alternation of blue and white shades.
I therefore readily agree with your answer, especially since the origin seems to me to be hydrothermal in nature.
The structure (AMS-data: Pluth J J, Smith J V - 2002) is obviously complex but seems ordered.
However, along the "a" axis, this unit cell surprises me a lot.
I'm asking myself a neophyte question, isn't it a semi-crystalline structure, as we find in some polymers?
The crystalline germs could be spherulites.
A thin section would highlight the Extinction Crosses of Malta, in XPol).
Excuse my curiosity.



Ajoite-AMS-data.jpg
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Ajoite-AMS-data.jpg


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Roger Warin




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PostPosted: Aug 27, 2021 22:45    Post subject: Re: Ajoite From Messina  

Hello,
This photo is taken with a binocular (8X).
Difficult focusing, stacking of 33 shots.
We cannot say that they are rectilinear needle-like crystals.
The deposit of ajoite takes place during a first stop of the crystallization of quartz (or during a slowing down).
Then the quartz resumes its growth.
The aggregate of ajoite is found incorporated into a kind of silica gel before it crystallizes, it seems to me. We would thus have this formation of space shaeves.
What do you think ?



Ajoite#1-01-AB-1_R.jpg
 Mineral: Ajoite
 Locality:
Messina Mine, Musina (Messina), Vhembe District, Limpopo Province, South Africa
 Description:
 Viewed:  1769 Time(s)

Ajoite#1-01-AB-1_R.jpg


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