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Termination in a tourmaline crystal
  
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marco campos-venuti




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PostPosted: Aug 28, 2018 08:37    Post subject: Termination in a tourmaline crystal  

I had this green tourmaline crystal on a recent trip to Brazil. It comes from Barra de Salinas pegmatite. It seems to me a quite unusual termination. Most of crystals from pegmatites have a lower symmetry, but this crystal has a very high symmetry.
Any comment? Can it be a clue for a different composition?



IMG_1370.JPG
 Mineral: tourmaline
 Locality:
Barra de Salinas, Coronel Murta, Jequitinhonha, Minas Gerais, Brazil
 Description:
 Viewed:  540 Time(s)

IMG_1370.JPG



IMG_1373.JPG
 Locality:
Barra de Salinas, Coronel Murta, Jequitinhonha, Minas Gerais, Brazil
 Description:
 Viewed:  543 Time(s)

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Pete Richards
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PostPosted: Aug 28, 2018 08:55    Post subject: Re: Termination in a tourmaline crystal  

A very nice crystal indeed, Marco! I have a small one from that pegmatite with a beautiful blue-green color, but it is not nearly as perfectly developed as yours.

I have had the opportunity to examine suites of dozens of tourmaline crystals from individual pockets from the Havey Quarry and Mount Mica in Maine. It seems likely that the chemistry in a particular pocket would be consistent throughout the pocket. But in all cases, some of the crystals are ideally developed while others are quite unbalanced in terms of symmetry - even missing some faces that should be there.

I don't know what accounts for this variablilty, but this observation suggests it is not chemistry!

It is also true that crystals from certain pockets are distinctly different in habit and color from those in pockets nearby. In this case, I suspect chemical differences may have played a role.

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John S. White
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PostPosted: Aug 28, 2018 13:13    Post subject: Re: Termination in a tourmaline crystal  

The Mercedes-like trio of narrow faces on the termination are quite odd. I have a large number of tourmaline crystals in my crystal collection but I do not have one like that. It resembles what you see in slices of liddicoatite. Very nice and green too.
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