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Strange Tourmaline formation containing a straw like channel
  
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MSrockhound




Joined: 08 Oct 2008
Posts: 11
Location: Mississippi

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PostPosted: Jan 11, 2013 00:07    Post subject: Strange Tourmaline formation containing a straw like channel  

I was offered this specimen recently and was curious as to how it could have formed, how rare this is, and if this is something I should purchase before its too late. I enjoy having a few atypical specimens and have never seen one like his before, also any insight on this specimen would be appreciated, all I know is that it is afghani in origin.

Cheers,
Chris



537187_318151384963323_547929066_n.jpg
 Description:
Tourmaline
Afghanistan
20 mm x 6 mm
 Viewed:  7222 Time(s)

537187_318151384963323_547929066_n.jpg



582384_318151308296664_1926986464_n.jpg
 Description:
Tourmaline
Afghanistan
20mm x 6mm
 Viewed:  7195 Time(s)

582384_318151308296664_1926986464_n.jpg


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Riccardo Modanesi




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PostPosted: Jan 11, 2013 06:25    Post subject: Re: Strange Tourmaline formation containing a straw like channel  

Hi MSRockhound!
This is a typical elbaite from the southern Asian basin (Afghanistan, Pakistan, India etc.). The inclusions are made by growth channels and some fractures. If you see it by a microscope, it's not to exclude you will see some mineral inclusions as well! Sometime mineral inclusions are very nice and interesting!
I hope I was useful for you. Greetings from Italy by Riccardo.

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Hi! I'm a collector of minerals since 1973 and a gemmologist. On Summer I always visit mines and quarries all over Europe looking for minerals! Ok, there is time to tell you much much more! Greetings from Italy by Riccardo.
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Ru Smith




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PostPosted: Jan 12, 2013 11:38    Post subject: Re: Strange Tourmaline formation containing a straw like channel  

Very interesting specimen.

There is an excellent discussion of these "hollow tourmalines" here:
https://www.minsocam.org/msa/special/pig/PIG_CQ/PIG_CQ_hllw_tur.html
(link normalized by FMF)
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Ru Smith




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PostPosted: Jan 12, 2013 11:54    Post subject: Re: Strange Tourmaline formation containing a straw like channel  

The end-on view is not a very clear image, but gives an impression that there is not a simple empty trigonal prism along the axis of the crystal. Perhaps this could be an example of skeletal growth from a highly supersaturated solution as opposed to the selective dissolution mechanisms discussed in the "PIG" thread.
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Josele




Joined: 10 Apr 2012
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PostPosted: Jan 12, 2013 20:02    Post subject: Re: Strange Tourmaline formation containing a straw like channel  

I have a tourmaline, also from Afghanistan, with a similar growing pattern type and some "holes".

And another one from Pakistan that shows a small portion of overlaping exterior layer creating a void space.

Maybe Chris specimen is an extreme example of this growing pattern type.



turma11.jpg
 Description:
It looks like grown in round or helicoidal layers, leaving void spaces in some places.
Nuristan, Afghanistan.
8,5 x 3 x 2,5 cm
 Viewed:  6911 Time(s)

turma11.jpg



turma12.jpg
 Description:
In this termination and in middle section can see the helicoidal growing pattern.
 Viewed:  6921 Time(s)

turma12.jpg



turma14.JPG
 Description:
This termination has a "negative crystal" at the tip of his beveled pyramid, with well defined faces.
Down left there is a dark void space between tourmaline prism walls.
Both "holes" are partially filled with a late stage white mineral.
 Viewed:  6901 Time(s)

turma14.JPG



T22.jpg
 Description:
Dark green / blue / black cap tourmaline with a very crumpled perimeter.
Stak Nala, Haramosh Mts., Skardu District, Baltistan, Pakistan.
10,5 x 6 x 5 cm.
 Viewed:  6909 Time(s)

T22.jpg



T24.JPG
 Description:
Combination of prism faces creating a fold. A sub-parallel crystal took profit of it.
 Viewed:  6897 Time(s)

T24.JPG



T25.JPG
 Description:
Detail.
 Viewed:  6892 Time(s)

T25.JPG



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