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Schorl
  
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Jim Wilkinson




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PostPosted: Jan 16, 2021 21:36    Post subject: Schorl  

I believe this is Schorl. I collected it in Montgomery County Maryland, USA in the 1960s.


schorlhcc.jpg
 Mineral: Schorl
 Dimensions: 6 X 3.5 cm
 Description:
Now in local community college collection
 Viewed:  1696 Time(s)

schorlhcc.jpg


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Volkmar Stingl




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PostPosted: Jan 17, 2021 01:26    Post subject: Re: Schorl  

Jim, Schorl is black Tourmaline.
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alfredo
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PostPosted: Jan 17, 2021 02:06    Post subject: Re: Schorl  

Tourmaline analysis is extremely difficult, a chemically very complex group whose individual species can often not be identified even if one has an x-ray diffraction pattern or an EDS analysis. Even professional mineralogists may lack the necessary instruments to identify all the tourmaline group members. And the group gets more and more complex as the years go by. To make it even worse, it is not at all uncommon to have two or three different species present as concentric layers in one single tourmaline crystal!

Collectors traditionally think of schorl as being the black tourmaline, but many other tourmaline species can be black too, including dravite (no, it's not always brown!), uvite, fluor-uvite, oxydravite, foitite, povondraite, fluorbuergerite.... and so on.

Unless one is dealing with specimens from a very well studied locality that have been analyzed by a tourmaline expert (and I do mean a tourmaline expert, not just any mineralogist) then it is best to just label them "Tourmaline".... such a beautiful name! Why change it?
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James Catmur
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PostPosted: Jan 17, 2021 04:38    Post subject: Re: Schorl  

Thank you Alfredo, great explanation of why we should avoid guesses with Tourmaline. I collected specimens in SE Pennsylvania in the 1970s that I have always considered to be Schorl as they are black, but I think I should change the labels!
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Jim Wilkinson




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PostPosted: Jan 17, 2021 14:33    Post subject: Re: Schorl  

Do you think the label of my post should be changed? All my mineral books label black tourmaline as schorl but if there is recent evidence to the contrary?
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Jim Wilkinson




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PostPosted: Jan 17, 2021 15:28    Post subject: Re: Schorl  

This was my first post to this forum as a new member and I was not expecting any comments. So when I saw three comments I was surprised and interested. I thought maybe someone might say something like interesting specimen from an underrepresented location etc. But instead there was a discussion on the proper naming. All my references label black tourmaline as schorl. I am an amateur and thus do not have the latest research. Should I not have joined your group because of my amateur status?
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Josele




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PostPosted: Jan 17, 2021 17:33    Post subject: Re: Schorl  

Jim, no problem, we all are amateurs here, even those with high mineralogical level they have something to learn.

In addition to difficult determination of the species in tourmaline group, it often turns out to be a solid solution of two or more species.
All papers I have read about black tourmaline in pegmatites indicate that they are intermediate members of schorl-foitite series. Another reason to label with the generic name tourmaline is it is more than unlikely a pure end member of the series.
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alfredo
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PostPosted: Jan 17, 2021 17:34    Post subject: Re: Schorl  

Not at all, Jim, you're most welcome here! And most of us are amateurs, some for many more years than others, but we all had to start somewhere.

Don't worry too much about the labeling, would be my advice anyway. If you call it "Tourmaline" then you'd be 100% correct and no one will complain except a few people who we call "systematic rare species collectors", in other words the "splitters". Students of Nature, whether that be plants or minerals, are divided into two camps, the "lumpers" and the "splitters". The splitters want everything named down to it's "species" level and think a "group" name is just not good enough for them. The "lumpers" - well, you probably already guessed their attitude.

If you call it "Schorl" instead of Tourmaline, most collectors will understand exactly that you mean a black tourmaline, and only a few obnoxious pedant types (like me) will ever ask you whether it was properly analyzed. ;))
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Tobi




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PostPosted: Jan 18, 2021 06:13    Post subject: Re: Schorl  

I agree Jim, you did absolutely right joining us - we all started as amateurs!

But the guys are right, correctly identifying tourmalines can be tricky and not every black tourmaline is a schorl - and thus the "black tourmaline" label on your specimen is for sure the best way to name it correctly :-)

Best regards
Tobi
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Roger Warin




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PostPosted: Jan 19, 2021 17:38    Post subject: Re: Schorl  

Hello,
Tourmaline is my favorite mineral, because its structure is such that it is a lesson in tolerance and philosophy. Nations on Earth should emulate it.
It crystallizes at the end of the crystallization of the granites, in pegmatites. All the impurities of these massifs rejected by the crystals (quartz, feldspars, micas) are found in the residual hydrothermal solutions. And there, the tourmaline opens its crystalline lattices to accept these cations rejected by the other crystallizations.
Geologists call it a pegmatite garbage can.

Their tolerance leads to all these multiple varieties (see Glossary), some opaque and others polychromatic, up to colorless achroite (variety of elbaite) as on the island of Elba.
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Jim Wilkinson




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PostPosted: Jan 19, 2021 22:12    Post subject: Re: Schorl  

Thanks Tobi!
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