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Rei

This winter's been horrible, one of the worst on record. There've been few times where's been more than three days between storm warnings. The biggest hit my land with 130 mile per hour winds, ripping down 2/3rds of my windbreak and flipping my storage crate over (among the damage, about 20 large windows totally shattered). Just a terrible, terrible winter.

But today was lovely and the snow has begun to melt from the mountains... and so I got my first real chance to go rock hunting again. And of course I wasn't going to miss that! I decided to explore a place where I previously found zeolites to see what I could find.

But, some pictures of the trip and the local geology. :)

Rei

Okay, now for the finds. I haven't had a chance to do tests yet, but I'm guessing stilbite? Maybe for all of them? They'll be sort of hard to test but I'll do my best when I've got a chance.

Rei

A few more pics...

Rei

So anyway, that's it for this trip. Any answers, tips, or general thoughts on the above? :)

vic rzonca · Joined: 18 Nov 2008 Posts: 820 Location: MA

Great post Rei. Some of that territory looks as though it just cooled off. The image of the colored river cobbles is wonderful.

Rei

The colors were even more impressive in person. The purple is particularly striking.

Haha, well, from a geological perspective it's really young ;) The whole area only started forming a little over 3 million years ago. The last eruption in the region was about 100kya, although there may have been intrusions since then - but the volcano is believed to be extinct (almost everything here is a volcano ;) ). Glaciers ripped out the U-shaped valley during the various ice ages, and the river has carved a pretty impressive canyon through its bottom, so one can access the older rocks.

There's of course always been - and still are - hydrothermal fluids acting on the rock; typical geothermal wells today in the region are usually between a couple hundred and a thousand meters deep. So there's of course ample possibility of not only subterranean modification of rocks, but also historic features (hot springs, fumaroles, etc) that have since gone extinct.

Need to stop this post early, my parrot is on the floor trying to eat my newfound zeolites. :Þ

Jordi Fabre

Rei

I've never ordered a test before, how would one go about finding a company to do it? Would I have to send a sample internationally?

Jordi Fabre

Rei

Thanks - I'll check for the PM :). Also, just did a hot vingear test on the flaky interior growth of *52/*53, and got significant bubbling (I did a control water test to be sure), so that secondary growth does indeed appear to be calcite.

I love living in a place where one can find such minerals just sitting on the surface near, and sometimes on, my land, right outside of the city where 2/3rds of the population lives, in a country bigger than Ireland and Kentucky.

Makes one wonder what's underground and what's further afield. :)

Mike Wood · Joined: 16 Dec 2010 Posts: 456 Location: Northern England

Great post Rei and thanks for sharing it with us. Nice to see the land again, re-emerging from the winter snow!

I'll have a go at some of the questions:-
The green blobs on the black stuff is all the same lichen, just the black part is previous growth, maybe last years.
Most of your specimens collected look like Stilbite, whether Ca, Na, or K - rich is only detectable by lab work. K - rich stilbite (Barrerrite, as Jordi stated above) is the rarest form by a long way. The crystals look large and well-formed, and quite 'fresh', meaning transparent. You could try a water-spray, or clean them under cool running water and use an artist's paintbrush to dislodge the dirt particles. Bleach might be necessary to remove any algae (lichen).
It would be worth your while to dig around in the area where you found these large stilbites, they look pretty good and there will likely be large geodes, probably formed in the same lava flow at the same horizon (layer) for a limited extent.

The small spiky mud-covered crystals around the edges of the stilbite specimen is likely to be a zeolite mineral, such as mesolite (or natrolite or scolecite), or laumontite.

The small sparkly ball-like aggregates of crystals in the smaller cavity look rather like prehnite (not a true zeolite but often with) but could also be quartz... not too sure.

The pale-coloured dykes could be an acidic magma, similar to rhyolite or pitchstone.
The purple rock next to the big dyke is likely to be enriched in iron, probably from hydrothermal solutions which are vigorous in Iceland, like you say...
The green coloured rocks under the purple coloured rocks look also iron-rich, but in the 'reduced' state chemically speaking (Fe2+, rather than Fe3+ for the 'oxidised' iron). There may be a chance of finding pyrite crystals in the green areas...

I hope you get the chance to get out exploring and collecting more this Summer, the land is looking good, thanks again for the photo's.

Rei

Wow, thanks for all of the replies Mike!

I'm going to send several of these, plus some previously collected specimens, to Geo Spectra for analysis. I'd love to have a better idea of what I'm looking at and what I'm finding in each area :)

Okay, so it looks like all of the black is lichen, growing into the cracks between the crystals? Okay, then I'll probably remove it from the nicer specimens but leave it on the poorer quality specimens, as it has a sort of neat character to itself, with those dendritic growths.

Do any of these zeolites degrade in a manner that I should know about? I know, for example, that pyrite degrades (oxidizes) after being collected if not treated and/or stored properly.

Interesting if the pale parallel streaks are rhyolite dikes or similar (I'll check them out on another hike later this year I'll try to get over to them). Basalt is of course more common here but rhyolite is present, there's one rhyolite peak I know of about 13 kilometers away. Makes me wonder if they're from the same eruption. :) I also have some rhyolite in the glacial till on certain parts of my land which I always assume came from the peak, but perhaps it came from a dike much closer. Interesting - definitely warrants a closer look :)

Your comment about the green rock just made something click for me. Some of the chalcedony veins on my land have green in them, particularly one further to the west which yields this beautiful glassy green chalcedony. I had long assumed that it was copper that gave it the green, but iron here is much more common and I forgot that Fe2+ can give things a green color. The vein is only about 100 meters from a spot where there's bright red clay over "rotten" rock that crumbles easily - which especially given how rare clay is here, strongly suggests to me that it used to be the site of some acidic water flows. Something tells me I should take the time to do some more digging in the area :)

The same area also has some calcite veins - which obviously were either untouched or deposited later if there were acidic water - and some interesting quartz specimens, such as this sizeable weirdo (so far I've only rinsed it, no additional cleaning):

https://www.flickr.com/photos/54125007@N08/16594945734/
https://www.flickr.com/photos/54125007@N08/17009942577/
https://www.flickr.com/photos/54125007@N08/17009938697/
https://www.flickr.com/photos/54125007@N08/16594929664/
https://www.flickr.com/photos/54125007@N08/16594942024/
(links normalized by FMF)
Sure looks like it formed inside some other minerals that have since disappeared, though I haven't a clue as to what!

As for the place where I was finding the zeolites, I'd have to apply for permission to dig there, it's public land. But no need to dig at this point when one can still find these sort of specimens just sitting loose on the surface! I've only walked a rather small portion of the productive area, and could see sizeable pieces at areas that I decided not to take the time to get to (45° talus slope, it takes time to move up and down them). But yeah, I'm sure there's some gorgeous beauties just sitting underground there.

I probably won't hit that exact area again in my next several hikes - I want to explore some of the side canyons (there's tons) to see what else the mountain holds, and maybe hit the other side of the main canyon opposite the big zeolite area to see if the deposit extends over there too. There's just so much to see, I've barely gotten more than two kilometers from the main road in the country, 15 kilometers from the center of the city where 2/3rds of the population lives, haha ;) The zeolites are only 1km from the main road (by contrast, the valley that I've been hiking in is 7 1/2 kilometers long and up to 4 kilometers wide). Oh, and erosion (which is a big problem here) regularly exposes brand new stuff (by picking up beautiful stuff you're actually saving them, these pieces would probably end up crashing down into the river and be destroyed at some point in the next couple decades if just left there). Iceland really is a great place for rockhounds. :)

Anyway, thanks for the info! :)

Mike Wood · Joined: 16 Dec 2010 Posts: 456 Location: Northern England

Hi Rei, you're welcome, it would be interesting to see the lab results :)
The green and black lichen should be removable after soaking in a cheap chlorine bleach solution, but might still require gentle scraping to shift it. The minerals should be fine with bleach; they are in my experience, only thing is it takes a fair bit of rinsing and soaking in clean water to get rid of the smell!

A few zeolite minerals can degrade and fall apart due to dehydration, laumontite is most famous for this. Chabazite seems particularly prone to internal crazing, when left in direct sunlight after being exposed for the first time, even for just a few minutes. As a rule I place collected specimens in the shade immediately after extraction, unless it's very cloudy of course. This may be an effect of heating causing crazing, but I'm not sure. Stilbite should be ok, but will eventually go white and opaque if left in the sun.

The red clay on your land could be the top of an olivine-basalt lava flow that has completely decomposed, due to hydrothermal action. I think this is how bauxite is formed. There used to be bauxite (aluminium ore) mines in Northern Ireland, where there is of course a lot of basalt lava flows from the Tertiary period.

One more thing, the photo links don't work for me, without signing up for ya-how, that is ;)

Happy hunting!

Cheers, Mike

Rei

Wow, thanks for the warning about light - I had no idea! That's important to know! Should I do anything with any of my samples to prevent dehydration?

I'll just insert the above pics into this post. :)

I went out today to a beach where I heard one can find high quality spherulites today, as I don't yet have any in my collection. Didn't find any, but but I found some more pretty zeolites and some lovely prehnite (presumably) druse. Only one small patch of ground was productive, but still, I wasn't expecting anything like that, the ocean is a pretty destructive beast.

Seems like everywhere you walk off the path here and look down you can find something neat ;) Can't wait to try out this area, the geology should be totally different than my immediate vicinity:

https://www.geothermal.is/32-tjarnarhnjukshraun-vid-olfusvatnsa-xenolithes
(link normalized by FMF)

"The rock type is picrite crowded with olivine phenocrysts, which are enriched in the lowest part of the pillows from crystal settling. Crystal settling of plagioclase xenocrysts (bytownite) can also be observed in a porphyritic pillow lava in the same gorge north and south of the Mælifell unit. The lava is rich in gabbroic xenoliths, which are best seen in the section along Ölfusvatnsá. Their mineralogy varies depending on which primary phase predominates, but most common are feldspar- and olivine-rich ones."