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The snows are melting in the mountains... time for a zeolite hunt!
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Rei




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PostPosted: May 09, 2015 03:32    Post subject: Re: The snows are melting in the mountains... time for a zeolite hunt!  

Okay, the test results are in :)

* The most common mineral as expected is Stilbite-Ca. For example, s1480018.jpg (Kongurinn) is predominantly Stilbite-Ca. He roughly identified an asbestiform mineral in a cavity on the rock as a phyllosilicate of unknown type, probably serpentine group, but it would require XRD to know exactly which. He also found the same mineral as part of the sample that I sent of a bit of crystal with those brown radial growths, so I suspect that those radial growths are the same phyllosilicate as in the cavity.

* The large beach specimen that broke into two pieces is also stilbite, but it contains mordenite fibrous crystals as well.

* My suspected opal that I collected last year did indeed turn out to be opal, cristobalite type (too bad I've never run into any with play of colour around here, that'd be such a neat find! :) ).

* The samples from the beach that look like, for example, s1490024.jpg, are stilbite-Ca and heulandite-Ca; I presume that the fine druse would be the heulandite?

* The zeolites I recovered from my land last year turned out to be a different mineral species than those recovered in the next valley - they're scolecite. This makes sense; my land is rich in calcite veins, and scolecite is closer to the calcium end of the silica-rich zeolite spectrum. The beach, with its mordenite and heulandite, would be on the calcium-poor end. The neighboring valley is in-between on the spectrum, with its stilbite and epistilbite.

* My sample of s1480017.jpg seems to have gone missing. :Þ

Anyway, nice to see such a variety of results and to be able to put names on what I'm finding in my area! :)
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PostPosted: May 11, 2015 14:06    Post subject: Re: The snows are melting in the mountains... time for a zeolite hunt!  

Hi Rei, many thanks for sharing your test results with us! :-)
Interesting to see that the beach specimen with the fine 'cauliflower' stilbite-Ca crystals, was accompanied by heulandite-Ca! This is quite embarrasing for me, after swearing it was chabazite, followed by saying it might be apophyllite! Oops -_-
Just goes to show how wrong one can be, guessing what a mineral is by looking at a photo...and yes, the smaller drusy crystals on that specimen will be the heulandite-Ca.
Also interesting was the prescence of mordenite, a high-silica zeolite. On one of my earlier replies I nearly started on about silica content and the morphology of stilbite crystals... Basically in my experience (Isle of Skye zeolites) the 'cauliflower' stilbites would appear to be silica-rich as they are usually found there in the prescence of quartz, and mordenite (these are the first minerals in the cavity to crystallise). The mordenite needles can often be seen enclosed in the stilbite, if the transparency is good enough. Also on Skye the 'pointy' stilbite crystals (which are far more common) are never found with quartz... the range of silica content of stilbite is not very great (73 - 77% according to Tschernich). Quartz is not at all common on the Isle of Skye, but does occur in some abundance at Sgurr nam Boc, perhaps the best locality on Skye for size and variety of zeolites...
It's nice to confirm opal on your land! But as you say, it would be even nicer if it had some colour in it... keep looking, you might find some, stranger things have happened etc.
You certainly have a variety of zeolites on your doorstep; if you could find the epistilbite that would be really cool. I think yugawaralite has been found in that area as well (I spotted it on Mindat), in quite large crystals for the species, another rarity!

Cheers, Mike

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PostPosted: May 11, 2015 17:02    Post subject: Re: The snows are melting in the mountains... time for a zeolite hunt!  

Mike Wood wrote:
Hi Rei, many thanks for sharing your test results with us! :-)
Interesting to see that the beach specimen with the fine 'cauliflower' stilbite-Ca crystals, was accompanied by heulandite-Ca! This is quite embarrasing for me, after swearing it was chabazite, followed by saying it might be apophyllite! Oops -_-
Just goes to show how wrong one can be, guessing what a mineral is by looking at a photo...and yes, the smaller drusy crystals on that specimen will be the heulandite-Ca.
Also interesting was the prescence of mordenite, a high-silica zeolite. On one of my earlier replies I nearly started on about silica content and the morphology of stilbite crystals... Basically in my experience (Isle of Skye zeolites) the 'cauliflower' stilbites would appear to be silica-rich as they are usually found there in the prescence of quartz, and mordenite (these are the first minerals in the cavity to crystallise). The mordenite needles can often be seen enclosed in the stilbite, if the transparency is good enough. Also on Skye the 'pointy' stilbite crystals (which are far more common) are never found with quartz... the range of silica content of stilbite is not very great (73 - 77% according to Tschernich). Quartz is not at all common on the Isle of Skye, but does occur in some abundance at Sgurr nam Boc, perhaps the best locality on Skye for size and variety of zeolites...
It's nice to confirm opal on your land! But as you say, it would be even nicer if it had some colour in it... keep looking, you might find some, stranger things have happened etc.
You certainly have a variety of zeolites on your doorstep; if you could find the epistilbite that would be really cool. I think yugawaralite has been found in that area as well (I spotted it on Mindat), in quite large crystals for the species, another rarity!

Cheers, Mike


Whoops... I mentioned the epistilbite in the neighboring valley but forgot to mention the sample (not from this recent trip, but from my last) that was identified as epistilbite. So yes, I've already crossed that one off my list, haha ;) No yugawaralite yet... I'll need to keep my eyes out for it! The mindat map shows it as being all around my neck of the woods. Where does it fit in on the silica and calcium spectrum?
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PostPosted: May 11, 2015 17:40    Post subject: Re: The snows are melting in the mountains... time for a zeolite hunt!  

(According to Tschernich)
Yugawaralite contains 66 - 75% silica, and is always calcium-rich. It is a pressure-sensitive mineral and forms at low pressure. Associated with laumontite, quartz, calcite, analcime..

Strangely enough, and I wouldn't have believed this if I hadn't just read it, yugawaralite can stand almost anything, except HF! I don't think I would even try anything other than water/bleach if I was ever lucky enough to find a specimen. The crystals are very brittle, and sensitive to heat.

Well done for finding epistilbite, it is a rare mineral! Do you have a photo of it? Is it crystalised?

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PostPosted: May 11, 2015 18:37    Post subject: Re: The snows are melting in the mountains... time for a zeolite hunt!  

Okay, so here is the part that I sheepishly admit that I wasn't all that great at keeping track of what sample came from what when I sent them in ...



But I think I know which one it was. I'll attach some pics.



s1500029.jpg
 Locality:
Iceland
 Description:
The sample that came back as epistilbite was #9, which in my description I wrote "9. A number of my samples have this semi-fibrous growth pattern." The sample for #9 ("Trefjur") is brownish (as if dirty) and on dark rock.
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s1500029.jpg



s1520007.jpg
 Dimensions: 6cm
 Description:
So, I believe that this was the piece that I cut the sample from. But I'm not 100%.

I both love and dislike this specimen. I love its delicate form, although that also makes me worried and makes it harder to handle. It has a that almost furry inside, but it's not as neat or orderly as one would like (like matted fur), and it's pretty heavily stained (looks darker in person than in the pictures). I'm considering cleaning it (most of my zeolites are cleaning up very well with my approach of alternating between Waller solution and bleach), but I hesitate with this one.
 Viewed:  12744 Time(s)

s1520007.jpg



s1520008.jpg
 Dimensions: 6cm
 Description:
I wouldn't have guessed that this would come back as epistilbite because of its fibrous nature... but maybe it's not the fibrous stuff that he tested? That's my suspicion at least - maybe there's some fibrous material growing on epistilbite? The sample I sent in didn't have any loose fibers, it was just the substrate (I think).

Sending the whole thing in the mail would have been more illuminating, but it's as mentioned fragile.
 Viewed:  12754 Time(s)

s1520008.jpg



s1520009.jpg
 Dimensions: 6cm
 Description:
 Viewed:  12755 Time(s)

s1520009.jpg


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PostPosted: May 11, 2015 19:16    Post subject: Re: The snows are melting in the mountains... time for a zeolite hunt!  

I'll note that a different sample (Kongurinn), in addition to being primarily Stilbite-Ca, was identified as also having "Phyllosilicate. Asbestiform - possible serpentine group. Requires XRD". In some cases they were growing straight off the crystals. And the fibers there looked rather like the fibers here.

So my best guess is that the fibers are the same sort of asbestiform phyllosilicate that likes to grow on zeolites, and that the epistilbite is the substrate.
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PostPosted: May 12, 2015 15:30    Post subject: Re: The snows are melting in the mountains... time for a zeolite hunt!  

I would think that if there is any epistilbite on that specimen, it would be underneath the furry mineral, maybe the substrate as you say... the matted appearance is most likely due to the mineral getting wet. It's only when you break into a completely enclosed cavity that any fine, fibrous minerals will appear unmatted.
If you could bear to wash off the matted furry mineral (maybe just a small area) you might well find epistilbite underneath it! I would do it, but maybe you would want to find some more specimens before doing this...
If there is epistilbite on the specimen then I would hazard a guess that the furry stuff could be mordenite (both are silica-rich) rather than say, mesolite/scolecite/natrolite (which are generally much more common, and also rather less silica content). Though after my last guess from your previous photo's being spectacularly wrong, all bets are off!

As far as the phyllosilicate - asbestiform - possible serpentine group analysis is concerned, I won't even try and suggest what it might be; that's a completely different ball game ;-)

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