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Waterclear mineral from Nepal?
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Josele




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PostPosted: Dec 27, 2012 09:42    Post subject: Waterclear mineral from Nepal?  

Recently I came back from Nepal, where I was trekking around the Annapurnas.
In Kathmandu I met Eric Manandhar, who is a Nepalese mineral dealer specialized in Ganesh Himal quartz. He was very pleasant and invited me to visit his home and to see his private collection. As many dealers do, he keeps the best specimens for his collection. He showed me some of the most fabulous quartz I've never seen.

Also he showed me a unknown waterclear mineral perched to a quartz that I can not identify. My first impression for color and luster was Topaz but, to me, the crystal looks as monoclinic or triclinic more than orthorhombic. Also Topaz is not listed in Ganesh Himal nor in Nepal Mindat gallery.

Perhaps you will can help us. Very thanks for your comment.



GH0.JPG
 Description:
Unknown
Ganesh Himal, Nepal.
Crystal size: 8,1 x 4,3 x 1,3 cm
photo: Eric Manandhar
 Viewed:  36651 Time(s)

GH0.JPG



GH1.JPG
 Description:
Unknown
Ganesh Himal, Nepal.
Crystal size: 8,1 x 4,3 x 1,3 cm
photo: Eric Manandhar
 Viewed:  36705 Time(s)

GH1.JPG



GH2.JPG
 Description:
Unknown
Ganesh Himal, Nepal.
Crystal size: 8,1 x 4,3 x 1,3 cm
photo: Eric Manandhar
 Viewed:  36683 Time(s)

GH2.JPG



GH3.JPG
 Description:
Unknown
Ganesh Himal, Nepal.
Crystal size: 8,1 x 4,3 x 1,3 cm
photo: Eric Manandhar
 Viewed:  36753 Time(s)

GH3.JPG



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Jordi Fabre
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PostPosted: Dec 27, 2012 10:00    Post subject: Re: Waterclear mineral from Nepal?  

It could be an unusual crystal shape Quartz. By chance have you tested the hardness?
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PostPosted: Dec 27, 2012 10:58    Post subject: Re: Waterclear mineral from Nepal?  

No, I had no chance to check any properties. Sorry, I can not offer more data, only these pictures.
But I had many quartzs in my hands that day and I think is not quartz.

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PostPosted: Dec 27, 2012 13:03    Post subject: Re: Waterclear mineral from Nepal?  

Josele, if it is quartz, it is quite unusual. I had a chance to look at your entry on Nepal in the Spanish forum. Fantastic!
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PostPosted: Dec 27, 2012 13:16    Post subject: Re: Waterclear mineral from Nepal?  

I believe this crystal is albite. A fine crystal to be sure!
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PostPosted: Dec 27, 2012 13:51    Post subject: Re: Waterclear mineral from Nepal?  

Brilliant, Pete. Could it be the finest ever?
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PostPosted: Dec 27, 2012 18:00    Post subject: Re: Waterclear mineral from Nepal?  

vic rzonca wrote:
.... Could it be the finest ever?


Well, I'm not experienced enough to make such extreme comparisons, but I've not seen an equally gemmy and well-formed crystal of albite larger than about 1/10 the size of that one....

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PostPosted: Dec 27, 2012 18:16    Post subject: Re: Waterclear mineral from Nepal?  

Pete Richards wrote:
I believe this crystal is albite. A fine crystal to be sure!

Pete Richards wrote:
... I've not seen an equally gemmy and well-formed crystal of albite larger than about 1/10 the size of that one....

Thank you very much Pete, was not easy...
Pete, sorry for abusing your wisdom: do you think is a single or a twin crystal?
Greetings.



Albite {110}, {010}, {1-11}, modified.jpg
 Description:
Albite {110}, {010}, {1-11}, modified
 Viewed:  36436 Time(s)

Albite {110}, {010}, {1-11}, modified.jpg



Albite {-101}, {001}, {010}, modified.jpg
 Description:
Albite {101}, {001}, {010}, modified
 Viewed:  36426 Time(s)

Albite {-101}, {001}, {010}, modified.jpg



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PostPosted: Dec 27, 2012 19:14    Post subject: Re: Waterclear mineral from Nepal?  

Josele wrote:
Do you think this is a single or a twinned crystal?


Although albite is very often twinned, this crystal appears not to be. The common twin law for albite is twinning parallel to the large {010} faces, sometimes just one twin, sometimes repeated twinning. Based on the very good images you sent, I do not see evidence of albite twinning (or any other mode of feldspar twinning, for that matter).

The habit of this crystal reminds me of those I've seen from certain alpine vein occurrences in Europe and Canada. The alpine vein setting might be reasonable for this crystal as well, though that is hard to know when you've just seen a crystal in a dealer's showroom!

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PostPosted: Dec 27, 2012 19:48    Post subject: Re: Waterclear mineral from Nepal?  

I think there is the first time that I see an albite single crystal! Pete, thanks for open my eyes.
Albite is a common partner of Ganesh Himal quartz. Here there is more material from the same find:

The photo below in high resolution



P1010324.JPG
 Description:
Quartz specimen showing Tessin habit prism and Dauphiné habit rhombohedral face. The lower and central section of the prism are included by chlorite* arborescences and rutile* needles, and in the middle-upper by some actinolite* or other amphibole needles. Albite and pericline law double twinned crystals attached to the bottom supports the set.
Ganesh Himal, Dhading District, Bagmati Zone, Nepal.
12 x 4 x 4 cm.
*just visually identified, not analyzed.
 Viewed:  36511 Time(s)

P1010324.JPG



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PostPosted: Dec 29, 2012 09:30    Post subject: Re: Waterclear mineral from Nepal?  

I tried to recognize the Miller indices on crystal faces. I assume that striations in front face are parallel to c axis.
Somebody can correct this?
Thanks for your help.



GH_iMiller.jpg
 Description:
Are Miller indices in right position?
 Viewed:  35507 Time(s)

GH_iMiller.jpg



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PostPosted: Dec 29, 2012 10:32    Post subject: Re: Waterclear mineral from Nepal?  

Josele wrote:
No, I had no chance to check any properties. Sorry, I can not offer more data, only these pictures.
But I had many quartzs in my hands that day and I think is not quartz.


Hi Josele and hi to everybody! I think we all must be sure about the hardness: if it is no lower than 6 (i.e. if it isn't scratched by an iron piece), it might be an albite. Without knowing the hardness, I can even think it is as low as 2, i.e. gypsum! Jordi, Carles and our Spanish friends know well there are beautiful gypsum crystals from Zaragoza appearing this shape!
Greetings from Italy by Riccardo.

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PostPosted: Dec 29, 2012 12:29    Post subject: Re: Waterclear mineral from Nepal?  

It is very difficult to determine by eye the Miller Indices of faces on a crystal from a few pictures, especially a low-symmetry mineral like triclinic albite. Jose's choices are quite good - I think most of them are correct.

I drew an albite with SHAPE, which computes the geometry of a crystal in terms of its indices and its symmetry and unit cell, and correctly displays its form from any angle. This drawing seems to confirm most of Jose's choices. However, to get the crystal edge shown in red to have the right orientation relative to the rest of the edges, I had to use the indices -1-20 rather than -1-30. I also was not able to determine the indices for the little triangular face labeled -2-21, but those indices are incorrect.

By the way, the drawing uses the crystallographic convention of placing a line over a number that is negative, rather than putting the minus sign in front of it.

Jose, good job!



albite.jpg
 Description:
 Viewed:  35512 Time(s)

albite.jpg



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PostPosted: Dec 29, 2012 19:48    Post subject: Re: Waterclear mineral from Nepal?  

Pete, very thanks for your help.
The small triangular face that I named mistakenly (-2-21), could be (-201)?
As you says, the face I named (-1-30) is (-1-20). Perhaps (-1-30) is the narrow bevel you can see at left in photo GH2.JPG?
Best regards.



{010}, {001}, {101}, modified.jpg
 Description:
 Viewed:  35425 Time(s)

{010}, {001}, {101}, modified.jpg



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PostPosted: Dec 30, 2012 17:21    Post subject: Re: Waterclear mineral from Nepal?  

Today I received more pictures from Eric Manandhar and accurate measures of crystal size. Is bigger than that I noted by eye. The actual size is 8,1 x 4,3 x 1,3 cm.

Thanks for all comments and special thanks to Pete Richards for crystallographic help.

All photos © Eric Manandhar



ab_GH1.JPG
 Description:
Albite (crystallographically recognized, not analized)
8,1 x 4,3 x 1,3 cm
Ganesh Himal, Dhading District, Bagmati Zone, Nepal.
Side view from -b axis.
 Viewed:  35291 Time(s)

ab_GH1.JPG



ab_GH2.JPG
 Description:
Side view from -b axis.
 Viewed:  35316 Time(s)

ab_GH2.JPG



ab_GH3.JPG
 Description:
The shiny face can be (22-1).
 Viewed:  35272 Time(s)

ab_GH3.JPG



ab_GH4.JPG
 Description:
Small polygonal faces of the corner can be (-221) and (-2-21).
 Viewed:  35300 Time(s)

ab_GH4.JPG



ab_GH5.JPG
 Description:
Shiny face is (010). The narrow bevel at left can be (130). Striated face at left is (120) and hard left (110).
 Viewed:  35280 Time(s)

ab_GH5.JPG



ab_GH6.JPG
 Description:
Shiny face can be (-111) with (-1-11) at right.
 Viewed:  35285 Time(s)

ab_GH6.JPG



ab_GH7.JPG
 Description:
View from c axis. Shiny face can be (-111) and the narrow, very striated, even stepped face at right can be (001). Below, in the shade, (-1-11).
 Viewed:  35286 Time(s)

ab_GH7.JPG



ab_GH8.JPG
 Description:
Albite (crystallographically recognized, not analized)
8,1 x 4,3 x 1,3 cm
Ganesh Himal, Dhading District, Bagmati Zone, Nepal.
Very glassy. Where there is no striations can see fingerprints perfectly.
 Viewed:  35248 Time(s)

ab_GH8.JPG



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PostPosted: Dec 31, 2012 13:51    Post subject: Re: Waterclear mineral from Nepal?  

Yesterday I uploaded some pictures of this crystal to Mindat gallery. I wrote to Amin C. Akhavan, Mindat supervisor of Nepalese specimens, asking if is acceptable crystallographic identification in this case. I just received the answer: Yes, this specimen is currently approved as albite in Mindat gallery.
I appreciate very much the help of Pete Richards to solve this identification, thank you very much Pete.

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PostPosted: Dec 31, 2012 15:03    Post subject: Re: Waterclear mineral from Nepal?  

These are 2 stunning specimens! I love that quartz!!!
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PostPosted: Dec 31, 2012 16:25    Post subject: Re: Waterclear mineral from Nepal?  

Albite seems reasonable--but the size, extraordinary! I also thought of gypsum when I saw the first photo; perhaps your friend could confirm for sure, that it is not a soft mineral?

I also thought of, perhaps, euclase for this crystal.

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PostPosted: Jan 01, 2013 11:37    Post subject: Re: Waterclear mineral from Nepal?  

At first, to wish you a healthy and happy new year.

Thanks for your inputs. I will ask Eric to check the hardness.

I was thinking that gypsum is not compatible with alpine-vein type minerals, but I'm not sure if can exist exceptions to this rule. Anyway, gypsum crystallographic parameters are, to me, different than I can see in these pictures.
Euclase yes is compatible with alpine-veins geological setting, but euclase crystal forms are, to me, also different.

I think that a good crystallographic examination of the pictures do not let many space to doubt: it has all parameters very like to a plagioclase and the transparency points to calcium absence. We must also bear in mind that plagioclases are the most common partner of Ganesh Himal quartz.

Fifty years ago, when XRD and microprobe were not easely available, a crystallographic checkup was the best way to identify a mineral specie when the crystal shows enough parameters, why not at present?

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PostPosted: Jan 01, 2013 13:56    Post subject: Re: Waterclear mineral from Nepal?  

I agree that gypsum seems most unlikely, and that euclase is more possible but the typical morphology is rather different from this crystal. My main misgivings about identifying this as albite are the lack of any indication of cleavage, even as minor cracks, and the apparent lack of twinning, which is very commonly present in albite crystals, either as simple contact twinning (on 010) or as repeated twinning.

It is true that fifty (or perhaps eighty) years ago crystallographic examination was one of the main means to identify minerals. But this was done with quite precise measurements made using a two-circle reflecting goniometer, able to measure angles to ± 2' of arc. If we could put this crystal's little brother on a goniometer, we could easily verify whether its interfacial angles correspond to those known for albite. That's a level of precision that cannot be obtained from studying two-dimensional images by eye, however.

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