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Sold as “Green stilbite”
  
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Charly H




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PostPosted: Sep 15, 2021 20:14    Post subject: Sold as “Green stilbite”  

But it is not that. The location is Iceland but I’m not sure which region. Approximately 4” by 3.5” vitreous luster that’s hard to see in static photos. I recognize some greenschist, garnet and serpentine, maybe some amphibole and actinolite? Chlorite? I can’t find anything similar by search or Audubon guide. I do not understand how to tell a zeolite apart from this but I know it’s not one. I do not understand what greenschist facies means but I was told it’s that. What is this thing please?
I don’t know how to post a video for better ID
Thank you



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Bergur_E_Sigurdarson




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PostPosted: Sep 15, 2021 20:31    Post subject: Re: Sold as “Green stilbite”  

I'm from Iceland, and this doesn't look like anything from my country ....at all.
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Matt_Zukowski
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PostPosted: Sep 15, 2021 22:29    Post subject: Re: Sold as “Green stilbite”  

Sometimes stilbite can present with chlorite inclusions, but your piece doesn't look like any of this material that i have seen. That said, all i have is to go on is one picture, so perhaps my impression is wrong. The picture doesn't show any vitreous luster - are you sure about this characterization of your sample?

As to greenschist facies, you should do a google search where you will learn that this refers to low grade metamorphic rocks characterized by a suite of minerals including chlorite. Your google search will show all kinds of pictures that you can compare against your sample.

How sure are you about the specimen being from Iceland?
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Jordi Fabre
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PostPosted: Sep 16, 2021 00:42    Post subject: Re: Sold as “Green stilbite”  

It looks like a Heulandite with Celadonite inclusions from Eyrarfjall Mountain, Hvalfjörđur.
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Charly H




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PostPosted: Sep 16, 2021 05:55    Post subject: Re: Sold as “Green stilbite”  

Matt_Zukowski wrote:
Sometimes stilbite can present with chlorite inclusions, but your piece doesn't look like any of this material that i have seen. That said, all i have is to go on is one picture, so perhaps my impression is wrong. The picture doesn't show any vitreous luster - are you sure about this characterization of your sample?

As to greenschist facies, you should do a google search where you will learn that this refers to low grade metamorphic rocks characterized by a suite of minerals including chlorite. Your google search will show all kinds of pictures that you can compare against your sample.

How sure are you about the specimen being from Iceland?


Thanks! About the specimen being from Iceland this is what the seller told me that is all I have to go by. The green part on top is quite shiny but only at certain angles, which is why I said it’s hard to see and a video shows it better, kind of like moonstone/feldspar if that makes sense. I googled that and I understand that greenschist facies refers to a group of minerals but I don’t know which one this is.
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Charly H




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PostPosted: Sep 16, 2021 05:57    Post subject: Re: Sold as “Green stilbite”  

Jordi Fabre wrote:
It looks like an Heulandite with Celadonite inclusions from Eyrarfjall Mountain, Hvalfjörđur.


Thank you! I thought it looked like heulandite/celadonite that yielded the closest images by search, still can’t find any quite like this piece. Having a location helps thank you so much!
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Charly H




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PostPosted: Sep 16, 2021 10:12    Post subject: Re: Sold as “Green stilbite”  

Charly H wrote:
But it is not that. The location is Iceland but I’m not sure which region. Approximately 4” by 3.5” vitreous luster that’s hard to see in static photos. I recognize some greenschist, garnet and serpentine, maybe some amphibole and actinolite? Chlorite? I can’t find anything similar by search or Audubon guide. I do not understand how to tell a zeolite apart from this but I know it’s not one. I do not understand what greenschist facies means but I was told it’s that. What is this thing please?
I don’t know how to post a video for better ID
Thank you


I posted a video on YouTube so you can better see the optical properties of this mineral. Thanks for your help everyone!

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Bergur_E_Sigurdarson




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PostPosted: Sep 16, 2021 10:36    Post subject: Re: Sold as “Green stilbite”  

I'd like to reiterate, this piece is very unlike any material I've seen from Iceland.
Most of my collecting has been in the Hvalfjörđur area, around Eyrarfjall in fact.

Here is the link to some of my finds from that area
https://www.mineral-forum.com/message-board/viewtopic.php?t=5710

The areas that have celadonite, it is usually a very thin coating of the vug and then the xls grow over that. Never seen it included.

In addition to having collected quite a lot around there I've also reviewed pretty much every image on mindat of Icelandic minerals and do not remember anything similar.
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Charly H




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PostPosted: Sep 16, 2021 10:54    Post subject: Re: Sold as “Green stilbite”  

Bergur_E_Sigurdarson wrote:
I'd like to reiterate, this piece is very unlike any material I've seen from Iceland.
Most of my collecting has been in the Hvalfjörđur area, around Eyrarfjall in fact.

Here is the link to some of my finds from that area
https://www.mineral-forum.com/message-board/viewtopic.php?t=5710

The areas that have celadonite, it is usually a very thin coating of the vug and then the xls grow over that. Never seen it included.

In addition to having collected quite a lot around there I've also reviewed pretty much every image on mindat of Icelandic minerals and do not remember anything similar.


Yes, I totally believe you. I can’t find anything similar from that region or Iceland otherwise, it looks like nothing I have found online to be honest. This is just what the seller told me, “green stilbite from Iceland.” It sort of resembles some stuff from India but nothing really that similar. How can you guys tell it’s celadonite vs chlorite? And how certain that it is heulandite? I definitely see garnet and greenschist but I am so curious as to what the rest of it could be.

**mouthwatering specimens by the way I would love to go collecting in Iceland!!
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Pete Richards
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PostPosted: Sep 16, 2021 15:44    Post subject: Re: Sold as “Green stilbite”  

It bears emphasis that garnet is the name of a mineral, while greenschist is the name of a metamorphic rock. I don't claim to be a petrologist, but I believe "greenschist" implies a certain range of temperatures and pressures, and is inconsistent with typical garnet. So something seems to be wrong here. If nothing else, it's confusing to say a specimen contains a mineral and a rock, as if the two were equal.

Zeolites typically do not occur with metamorphic rocks, unless (as happens in a few places, but not Iceland) the zeolites grow on metamorphic rocks much later than the metamorphism, in which case the fact that the rock is metamorphic is irrelevant except that it may bring zeolites in contact with other minerals that are typically metamorphic.

Finally, celadonite is a green mineral that belongs to the mica group, while chlorite is now the name of another, related group. Both are green, and one cannot tell for sure which one is in hand without technical study. However, most frequently chlorite minerals are metamorphic while celadonite is more associated with basalts and other lower-pressure environments.

I'm writing from what is in my brain. I do not guarantee that all comments are exactly correct! but they may guide a more nuanced discussion of this mysterious rock.

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Charly H




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PostPosted: Sep 17, 2021 06:28    Post subject: Re: Sold as “Green stilbite”  

That definitely helps. Sorry I am a moron. I think I meant chlorite schist but that’s probably the wrong terminology too. I have no idea what I’m looking at at all now. I guess I just have a green rock that’s not from Iceland. Thank you for your help!! I really appreciate the explanation the facies kinda make sense now.
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alfredo
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PostPosted: Sep 17, 2021 07:46    Post subject: Re: Sold as “Green stilbite”  

Certainly looks like heulandite crystals colored by inclusions of celadonite, and almost certainly from a basalt rock rather than a metamorphic rock, but whether it's from Iceland or India or elsewhere I can't say. If we were guessing or betting, most people would say "India", just because the enormous quantities of such material coming from the Deccan Traps dwarfs the amounts found anywhere else.
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