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Tourmaline
  
  Index -> FOR BEGINNERS: What is it? Where is it from?
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Mathias




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PostPosted: Jul 01, 2020 06:12    Post subject: Tourmaline  

Dear friends,

I got this specimen recently as part of 60 specimen parcel.

It was labeled "Tourmaline".

That's it.......no other information given.

Is there anybody out there who can help.....
To give me a clue where it might be from?

Thanks,

Mathias.



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Volkmar Stingl




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PostPosted: Jul 01, 2020 23:21    Post subject: Re: Tourmaline  

Looks like tourmalines from the Malkhan pegmatite field in Transbaikalia (at least the color). But I am not sure if it is really tourmaline. A picture of the top faces would help.
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Mathias




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PostPosted: Jul 02, 2020 02:02    Post subject: Re: Tourmaline  

Dear Volkmar,

Thanks for your reply. Here are some more pictures.
Perhaps it's not Tourmaline, it was just what was on the label.

Thanks,
Mathias



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Peter Lemkin




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PostPosted: Jul 02, 2020 04:37    Post subject: Re: Tourmaline  

The color is rare [but not impossible] for tourmaline. The parallel grooves on one side in one photo are sometimes indicative of tourmaline...but you have to do some work other than show photos. What is the hardness? streak? specific density? have a goniometer to measure the angles between faces?
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Tobi




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PostPosted: Jul 02, 2020 05:54    Post subject: Re: Tourmaline  

Peter is right, more information would be helpful to identify this crystal ...
But I also agree with Volkmar, according to the photos this is most likely rubellite, maybe from Malkhan pegmatite in Russia.

Regards
Tobi
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Jesse Fisher




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PostPosted: Jul 02, 2020 10:24    Post subject: Re: Tourmaline  

Exploitation of the Malkhan pegmatites is fairly recent. If it comes from an older collection, then this is not likely. It might help to know when and where the collection was assembled.
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Josele




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PostPosted: Jul 02, 2020 16:14    Post subject: Re: Tourmaline  

Another vote for tourmaline from Malkhan pegmatite field. This dark purple color is typical from this location.
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Mathias




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PostPosted: Jul 05, 2020 06:45    Post subject: Re: Tourmaline  

Thanks for everyone's input on this specimen.

I don't have a goniometer, and if I had one, it would be difficult to use since the specimen is glued on an acrylic display base.

I got this parcel of specimen from someone I met (as a vendor) at a small local mineral show (2019), he was selling relatively good specimens for too low prices, and I asked him if he had more at home. He gave me his address. Then, a few weeks later, I visited him (35 km driving from where I live) and since then I bought approximately 600 specimens from him (I went there some 15 times).

I bought all his international specimens, and what's left are 5 showcases with specimens from Becke Oese and Holzen, which he mined all by himself during 20 years. These 2 quarries mainly produced (both are no longer open for collecting) Calcite, Dolomite, Barite, Pyrite, Marcasite, Galena, Quartz, some Malachite. Many of which are really aesthetic specimens.

The person I bought these specimens from is between 70 and 80 of age and has no outlet for his minerals, and is no longer interested in collecting, for the past 10 years. So these specimens were just stored in showcases in a dark room.

I think I paid him more per specimen than a whole-collection-buyer would have done but less than the market price. This feels reasonable.

My wife always asks me "when will you stop buying all these minerals" because one day the same will happen to you. And she's probably right. And then I tell her that spending all this money on minerals pays back right now, in terms of fun.
The depreciation period is from now until I'm 80 (If i ever reach this age).

Thanks again for your help in identifying some of these specimens.
Most of the 600 specimen are on my Instagram account (NFS); marc.eggen
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Roger Warin




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PostPosted: Jul 05, 2020 07:34    Post subject: Re: Tourmaline  

I am 86 years old and tourmalines are my food.
Try to photograph your specimen in profile. You will get on a plane, the profile of your sample which you can then estimate the angle.
Mineralogy is better than sleeping pills ...
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Josele




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PostPosted: Jul 05, 2020 09:04    Post subject: Re: Tourmaline  

Mathias wrote:
... I don't have a goniometer, and if I had one, it would be difficult to use since the specimen is glued on an acrylic display base. ...
The specimen seems to be glued with thermal silicone. If this is the case, a drop of ethyl alcohol between specimen and glue will be enough to release it easily without any damage.
You don't need a goniometer, an angle protractor will do.


Mathias wrote:
... And she's probably right. ...
By definition, wife is always right!


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Bob Morgan




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PostPosted: Jul 05, 2020 15:53    Post subject: Re: Tourmaline  

From the photos it sure looks to be tourmaline - striations on prism, three shallow pyramidal faces with a central triangular termination.
One way to check the pyramidal faces is to hold another similarly shaped crystal aside it and see if faces from both crystals reflect light at the same angle for all three faces.
This won't give you precise angle measurements, but it should confirm it's identity.
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Bob Carnein




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PostPosted: Jul 05, 2020 16:12    Post subject: Re: Tourmaline  

Be aware that tourmaline has various pyramids that intersect the prism faces at various angles, some steep, others shallow.
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Roger Warin




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PostPosted: Jul 05, 2020 16:14    Post subject: Re: Tourmaline  

And the two poles are different.
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Josele




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PostPosted: Jul 05, 2020 19:44    Post subject: Re: Tourmaline  

Roger Warin wrote:
And the two poles are different.

Not necessarily. Although tourmaline belongs to 3m class of the trigonal system and does not have a symmetry center nor symmetry plane perpendicular to the c-axis, it can have the same rhombohedral termination on both sides.
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Peter Lemkin




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PostPosted: Jul 06, 2020 01:05    Post subject: Re: Tourmaline  

I still think a hardness test would be one of the first things to do.
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Bob Morgan




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PostPosted: Jul 06, 2020 07:30    Post subject: Re: Tourmaline  

My impression is that there is just one termination in the photos. Yes, there are different angles to be found on tourmaline pyramidal faces. It would require finding a matching one to make the reflection comparison. Find one that matches and has the same color and you may have a locality match.
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Jordi Fabre
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PostPosted: Jul 06, 2020 08:16    Post subject: Re: Tourmaline  

Bob Morgan wrote:
...Find one that matches and has the same color and you may have a locality match.

Maybe Sahatany Valley, Madagascar. Almost sure it is not Malkhan, it does not match the epoque nor the color tonality.
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