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Questionable gwindels

Posted by Harjo Neutkens  
avatar Re: Questionable gwindels
October 31, 2011 06:40PM
    
Thanks for the photos. The twist is much more prominent than I thought to be seeing in the first photo.
It sure looks very uncommon. As for now I'm afraid I haven't got a conclusive answer as to what governs the twist.
First I thought a bent Quartz rather than a twisted Quartz could be an option, but I've never seen Quartz bent around the c-axis, but then again, I haven't seen lots of things yet.... Looking at it it though the twist seems to be very consistent, almost too consistent for a bent crystal, so it might be a twisted Quartz crystal. Difficult one winking smiley
falk burger
Re: Questionable gwindels
November 03, 2011 03:39PM
As I research this further, it appears there are two crystals in parallel but slightly out-of-phase growth that is causing the twist. I'll consult Dana vol.3, as a friend suggested, for the proper terminology and further insight into how this happens. Please keep in touch about anything you may want to add..

Falk
Re: Questionable gwindels
November 03, 2011 04:32PM
    
Hi,

This is the best photo I could get of the top view of the quartz from Branchville, Connecticut.

© Joseph Polityka

© Joseph Polityka

Regardless, it is a rare locality specimen.

Best,

Joe
Re: Questionable gwindels
November 03, 2011 11:52PM
Joe, I can't see anything that would indicate a gwindel.
Looks more like 2 intergrown flat crystals that are slightly rotated with respect to each other.
I can't see any x faces, too.
Re: Questionable gwindels
November 04, 2011 01:54AM
    
Amir,

Thank you; I will change the information on my Mindat photo.

Best wishes,

Joe
avatar Re: Questionable gwindels
February 26, 2012 01:44AM
    
We just posted this to the mindat photo gallery, but would love to have confirmation that it is indeed a gwindel. It is from Giuv Valley, Tujetsch (Tavetsch), Vorderrhein Valley, Grischun (Grisons; Graub√ľnden), Switzerland. Note we have no reason to doubt it, but it would be nice to have expert confirmation.

Side View©

Looking down the top©

Thanks
Bob
avatar Re: Questionable gwindels
February 26, 2012 05:35AM
Looks like parallel crystals with a systematic twist, so yes.

Regards,
Ralph
Re: Questionable gwindels
February 26, 2012 09:07AM
Even if I am very late with my contribution, I couldn't help but enter the discussion on one of my home topics.
Going back to the first few posts, I agree with Amir almost all the way and may be able to answer a question of his.
One or two remarks, though: Numbers 13 and 14 are not clear on the photo, I would need a top view, too. These being gwindels is probable, though, as both localities are well known for producing quite a few gwindels.
No. 15 sure looks like a gwindel to me. Again, locality is known for gwindels and the piece just looks right.

About "transitional" gwindels: I think it's not a truly official term. What you often observe in gwindel-rich environments are a number of classic " flat-lying" gwindels (C-axis more or less parallel to cleft walls) and often a few gwindels that look like a hybrid between a classic gwindel and a single, upright point. You will see some (but not much) rotation and just a little stacking along C-axis. Kind of hard to describe. Let me go though my photo files and post a decent picture soon.

As for Falk's quartz (if you are interested in my opinion), I am not yet sure at what I am looking at. I can't recognize a diagnostic twist. I may need a top view (in this case, side view).

Andy
Switzerland
Re: Questionable gwindels
February 26, 2012 09:16AM
Two more things:
I'm very tempted to label Joseph's Connecticut piece as a "closed gwindel" (there seems to be some twist). However, I am not familiar with the geology in Branchville to say that this would make sense.
Jessica and Robert's piece is a gwindel, no doubt. What I do question, however, is the locality. This looks more like one of the new Cavradi gorge gwindels than a Giuv Valley piece. the light color, the thinness and the "openness" point away from the Giuv Valley. (By the way: The mistake wouldn't be dramatic, it's just a gorge opposite the Giuv Valley). But then again, the Giuv Valley has produced a variety of gwindels.

Cheers,
Andy
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