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Odd textures on this large beryl
  
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RussEpp




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PostPosted: Nov 23, 2020 22:13    Post subject: Odd textures on this large beryl  

This large green beryl has a termination that looks like hundreds of small mountain peaks. However, what I find really interesting is that 3 contiguous sides are smooth and 3 have a much rougher but distinctive texture. How could that happen and has anyone seen anything comparable. I believe the beryl is either from Madagascar or Mozambique. The first picture shows the termination and 2 of the rougher textured sides, the second picture a closeup of the texture of the rougher sides and the third picture, two of the smooth sides.


IMG_1425.JPEG
 Mineral: Beryl
 Description:
Africa
8.8x8.7x7.6cm
 Viewed:  1566 Time(s)

IMG_1425.JPEG



IMG_1426.JPEG
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IMG_1426.JPEG



IMG_1424.JPEG
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IMG_1424.JPEG


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James Tate




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PostPosted: Nov 24, 2020 10:17    Post subject: Re: Odd textures on this large beryl  

The surface appears to be possible melt-features to me. I've studied impactites from Africa near the Mozambique border area. This could be a sample involved within a high-energy event process that left a signature of likely impact-related temperature involvement, and mild shock features.

Certainly a possibility...and reason for the odd melt tektite-like texture.
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Duncan Miller




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PostPosted: Nov 24, 2020 11:28    Post subject: Re: Odd textures on this large beryl  

I think the rough texture is just natural etching of exposed surfaces, with the smoother faces protected by whatever mineral the crystal was embedded in originally.
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RussEpp




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PostPosted: Nov 24, 2020 11:46    Post subject: Re: Odd textures on this large beryl  

Thanks for the responses, the melting and etching are both plausible and interesting ideas. I initially doubted both, because it had appeared to me that the 2 textures were perfectly aligned with the faces, but after re-examining the specimen realized that the 2 different textures were not precisely aligned with the edges of the 3 faces, actually the smooth texture continued a few millimeters over the 4th face and likewise the rough "melted" texture is not perfectly aligned, (although very close).
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lluis




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PostPosted: Nov 24, 2020 11:53    Post subject: Re: Odd textures on this large beryl  

Hi, All

I think, if that serves for anything, that what says Duncan, etching, is the answer. Just I maybe differ in I think that could be an etching in preferential faces, as is seen in many other minerals.... Not necessarily covered by another mineral, just preferential etching...

With bets wishes

Lluís
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Bob Morgan




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PostPosted: Nov 24, 2020 13:28    Post subject: Re: Odd textures on this large beryl  

I concur with etching but not selective etching based on crystal structure. All prism faces are equivalent. It seems more likely that the crystal was partially exposed to the etchant, probably by being horizontal in a fluid with the smooth surfaces above the surface. What dissolution appears on them would be because of crystal flaws as in the deep crevasses of the smooth surfaces. And the edge between smooth faces would be more vulnerable to etching.

What a 'cool' crystal, far more interesting than a uniform beauty.
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John S. White
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PostPosted: Nov 24, 2020 14:53    Post subject: Re: Odd textures on this large beryl  

Definitely etching. I differ with Bob however as I prefer to think the smooth faces were protected. They were either in contact with another crystal or they were lying upon a surface that shielded them from the etchent.
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Fiebre Verde




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PostPosted: Nov 25, 2020 05:17    Post subject: Re: Odd textures on this large beryl  

RussEpp wrote:
This large green beryl has a termination that looks like hundreds of small mountain peaks...

Agree with Bob, that's a cool crystal which carries the memory of a tormented history.
Could you perhaps post a closeup of the termination as well?
Gerard
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RussEpp




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PostPosted: Nov 25, 2020 09:59    Post subject: Re: Odd textures on this large beryl  

Fiebre Verde wrote:
RussEpp wrote:
This large green beryl has a termination that looks like hundreds of small mountain peaks...

Agree with Bob, that's a cool crystal which carries the memory of a tormented history.
Could you perhaps post a closeup of the termination as well?
Gerard
Sure, as requested. This about the best I can do with my iPhone. Cheers, Russ


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Sante Celiberti




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PostPosted: Nov 25, 2020 14:52    Post subject: Re: Odd textures on this large beryl  

Definitely, a beautiful and interesting alternative to the usual smooth and lustrous pinacoid.
It's a pity you don't have information on the locality.
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RussEpp




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PostPosted: Nov 25, 2020 15:37    Post subject: Re: Odd textures on this large beryl  

Sante Celiberti wrote:
Definitely, a beautiful and interesting alternative to the usual smooth and lustrous pinacoid.
It's a pity you don't have information on the locality.


If anyone has any ideas where it came from or similar beryls to compare I would be very interested. I purchased this softball-sized specimen many years ago from a Californian seller on EBay. He had a poor out of focus picture of it and described it as a green and gold sculpture! I could see it was hexagonal and green so I thought- either apatite or beryl - what else could it be? My curiosity got the best of me so I took a chance for a relatively small amount of money and needless to say I was very pleased when it arrived.
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