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[Rei]

Two more :)

[Mike Wood]

I would think the climate in Iceland would be humid enough most of the time, to prevent dehydration of most zeolite minerals, except for laumontite which really needs to be kept in a permanantly wet environment (I keep mine in a cheap plastic see-through box with a lid, with water in it). Just keep them out of sunlight and away from direct heat and they should be fine :)

The weird quartz specimen with the holes in it looks like chalcedony, with calcite (probably) formally occupying the holes... I think I can see some thing resembling calcite in the last photo of that post.

The beach you went to looks promising if your last specimens were easily found! The first specimen with the interlocking thin platy crystals is stilbite, I have seen much of the same type of material on the Isle of Skye. The other specimens are also mostly stilbite but in a very different form! They look good and fresh and are good specimens; particularly the one with the chabazite crystals on. I know I'm being presumptious here but those clear pseudo-rhombohedral crystals look exactly like chabazite to me! Similar to rhombohedral calcite crystals of course; the acid test will decide!
Those 'cauliflower' stilbites are really neat. One crystal looks like it is forming a 'bowtie' shape, ie a double-terminated crystal. Good stuff.
Stilbite occurs in many different forms, but I reckon the two examples you have found are about the two extremes.
Of course, the crystals might be a bit worn by surf action, and might dry out a bit white. If there are any boulders around on the beach it would be worth breaking them up with lumphammer and chisels to see if there are any large fresh geodes inside - there will be, because that would be the source of your finds.

It's right what you say about minerals getting destroyed, by not picking them up and preserving them. What's the point of leaving a good specimen lying on a rocky beach when it will very soon get reduced to dust by the timeless pounding of the waves? Should be allowed ;)

[Rei]

[Mike Wood]

I've just been looking at the last photo's again and realised I had forgotten about apophyllite - which can look like chabazite when it is in small pinacoidal crystals. Some of the pseudorhombohedral (almost cubic-looking) crystals in the photo's appear to have a slightly curved face, which is more indicative of apophyllite where the pinacoidal face is often concave to a slight degree.
Chabazite is always of regular form in my experience, with flat smooth faces all equally lustrous.
Apophyllite has a vitreous lustre on the sides (pyramidal faces) and very often a more 'pearly' lustre on the end face (pinacoid). There are very often cleavage planes parallel with the pinacoid face, right down the length of the crystal. It occurs in a large variety of forms (habits), it isn't classed as a true zeolite but it often occurs with them.

Hope your trip to the canyon is enjoyable!

[Rei]

Interesting. Well, I've got a package ready to send out for ID, so I guess we'll find out!

[Rei]

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! :)

[Mike Wood]

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

[Rei]

[Mike Wood]

(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?

[Rei]

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 ...

:Þ

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

[Rei]

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.

[Mike Wood]

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 ;-)