<p>I have been observing a nepheline specimen under polarized light and found some interesting places. I have taken several images. The first shows a micro-geode with parallel polarizers, second with crossed polarizers. I wonder.. could these crystals inside be nepheline ? If not, what mineral could it be ? The thin section was labelled "nepheline". Also.. is the bubble real air bubble or anything else ?</p>

<p>Parallel polarizers:
<a href="https://i.sstatic.net/e9x2j.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/e9x2j.jpg" alt="Image with parallel polarizers"></a>
<a href="https://www.flickr.com/photos/violetplanet/30883853122/in/album-72157671897003403/" rel="nofollow noreferrer">https://www.flickr.com/photos/violetplanet/30883853122/in/album-72157671897003403/</a></p>

<p>Crossed polarizers:
<a href="https://i.sstatic.net/6CIIA.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/6CIIA.jpg" alt="Image with crossed polarizers"></a>
<a href="https://www.flickr.com/photos/violetplanet/30883853562/in/album-72157671897003403/" rel="nofollow noreferrer">https://www.flickr.com/photos/violetplanet/30883853562/in/album-72157671897003403/</a></p>

<p>I have also observed pyroxene crystals in Fe-solution (in parallel nicols could be mistaken with biotite), olivine and there should be nepheline. I have also found secondary quartz filling a cavity near olivine crystals. I    believe the original rock was some kind of basalt.</p>

<p>Thanks for help.</p>

CC BY-SA 3.0
2016-11-23T17:42:37.443Z
Hello, and welcome to Stack Exchange. By "nicols", did you mean "polarized filters"?
Daniel Griscom
CC BY-SA 3.0
2016-11-24T23:15:19.083Z
Probably not nepheline, it has much lower birefringence. This rules out most zeolites as well. Most likely a hydrothermal mineral though. Epidote pyrophyllite pumpellyite are possible? Amphibole? Ca-mica? Could be anything really. Can you get the optical properties of it?
Gimelist
CC BY-SA 3.0
2016-11-25T19:49:07.637Z
I have no idea. I am just learning the basic minerals while taking photos of anything, that seems like a good example to put on the internet so people interested in thin sections could learn from it. Reminds me of apatite or pyroxene though. 

I will give you two more links to similar structures that were in the same thin section. I fear that this is the only way I can help. 

https://www.flickr.com/photos/violetplanet/30368239033/in/album-72157671897003403/
https://www.flickr.com/photos/violetplanet/30912236761/in/photostream/
Petr Hykš
CC BY-SA 3.0
2016-11-26T02:21:40.513Z
@PetrHykš don't worry - that's not a "basic mineral". To be honest, it could be anything. Even if you get the optical properties getting it with 100% confidence is hard. This is a classic case where you need more advanced methods to do it (such as SEM-EDS for example).
Gimelist
CC BY-SA 3.0
2016-11-26T14:09:51.003Z
Good, thank you. :) Can you help me with one more thing ? I am wondering about the bubble in the micro-geode. Could it be real air bubble ? And how did it form ? I think that there was a bigger air bubble that was secondary fulfilled with solution and crystals. The pressure was rising and formed this almost spherical air bubble. Is it accurate ?
Petr Hykš
CC BY-SA 3.0
2017-02-05T23:40:38.557Z
Similar nepheline specimen.　jonathansmineralexchange.com/mont-saint-hilaire/villiaumite-fine-specimen-mineral-mont-saint-hilaire-quebec-002/
Takahiro Waki
<geology><mineralogy>
I have found this structure in thin section. What is it?
Petr Hykš
# I have found this structure in thin section. What is it?

(Asked by: username_0 on 2016-11-23)

I have been observing a nepheline specimen under polarized light and found some interesting places. I have taken several images. The first shows a micro-geode with parallel polarizers, second with crossed polarizers. I wonder.. could these crystals inside be nepheline ? If not, what mineral could it be ? The thin section was labelled "nepheline". Also.. is the bubble real air bubble or anything else ?

Parallel polarizers:
[![Image with parallel polarizers](https://i.sstatic.net/e9x2j.jpg)](https://i.sstatic.net/e9x2j.jpg)
<https://www.flickr.com/photos/violetplanet/30883853122/in/album-72157671897003403/>

Crossed polarizers:
[![Image with crossed polarizers](https://i.sstatic.net/6CIIA.jpg)](https://i.sstatic.net/6CIIA.jpg)
<https://www.flickr.com/photos/violetplanet/30883853562/in/album-72157671897003403/>

I have also observed pyroxene crystals in Fe-solution (in parallel nicols could be mistaken with biotite), olivine and there should be nepheline. I have also found secondary quartz filling a cavity near olivine crystals. I believe the original rock was some kind of basalt.

Thanks for help.

**Tags:** geology, mineralogy

> **Comments:**
> **username_1**: Hello, and welcome to Stack Exchange. By "nicols", did you mean "polarized filters"?  
> **username_2**: Probably not nepheline, it has much lower birefringence. This rules out most zeolites as well. Most likely a hydrothermal mineral though. Epidote pyrophyllite pumpellyite are possible? Amphibole? Ca-mica? Could be anything really. Can you get the optical properties of it?  
> **username_0**: I have no idea. I am just learning the basic minerals while taking photos of anything, that seems like a good example to put on the internet so people interested in thin sections could learn from it. Reminds me of apatite or pyroxene though.   I will give you two more links to similar structures that were in the same thin section. I fear that this is the only way I can help.   https://www.flickr.com/photos/violetplanet/30368239033/in/album-72157671897003403/ https://www.flickr.com/photos/violetplanet/30912236761/in/photostream/  
> **username_2**: @username_0 don't worry - that's not a "basic mineral". To be honest, it could be anything. Even if you get the optical properties getting it with 100% confidence is hard. This is a classic case where you need more advanced methods to do it (such as SEM-EDS for example).  
> **username_0**: Good, thank you. :) Can you help me with one more thing ? I am wondering about the bubble in the micro-geode. Could it be real air bubble ? And how did it form ? I think that there was a bigger air bubble that was secondary fulfilled with solution and crystals. The pressure was rising and formed this almost spherical air bubble. Is it accurate ?  
> **username_3**: Similar nepheline specimen.　jonathansmineralexchange.com/mont-saint-hilaire/villiaumite-fine-specimen-mineral-mont-saint-hilaire-quebec-002/  

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## 0 answers

