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[Rei]

So I've been having good luck on the chalcedony and especially crystal (primarily calcite) fronts of late. On a recent walk through my land I stumbled across an area whose rocks looked different - I was struck by the high olivine concentration mixed with high iron concentrations, and in some places streaks of white, as well as little amygdules and shiny flecks. Following a hunch, I checked the slope above there... and wow, it was a trove

Later, on a different slope I found a bunch of botryoidal specimens.

I assume most of this is calcite (because I know there's calcite in the area), but I haven't yet done a vinegar test. What I'm relly curious about however is the "hairy" / asbestiform structures which seem to blend into the crystals. Anyone have any clue what they could be?

All of this is rather dirty - it's straight from the ground, after all - but when my Iron Out comes after a couple months I'll give them a nice bath. :) The likelihood that they're calcite-bearing prohibits the use of acid.

[Rei]

A few more pics.

[dironot]

Great finds! Please post some photos of the specimens after cleaning. I am also VERY interested in seeing pictures of the hillside/area features you are describing.

[Michael Shaw]

Hi Rei,

You should check the hardness of your "botryoidal calcite." It looks more like chalcedony to me. This simple test will tell you quickly what you have.

Michael

[Rei]

[Jordi Fabre]

[Mike Wood]

Congratulations Rei, it looks like you have found some useful zeolites! Well, stilbite is good anyway. Nice crystals! They may only need washing in water to get the mud off.
The 'hairy' stuff is probably mesolite (one of the most common 'hairy zeolites) and if it isn't found clean, it is almost uncleanable. Very nice botryoidal chalcedony!
Was wondering if the first picture (with the greenish botryoids) might be prehnite, but it could still be chalcedony.

Nice one :-)

Mike

[Rei]

Thanks!

Not sure how to run any further tests without damaging them (aka, wouldn't really want to *dissolve* my zeolites by dunking them in HCl just to prove, yep, they were zeolites! ;) Hmm, maybe I could try to break off just one or two crystals and put them in a tiny container or on a microscope slide), but it's nice to have a good idea regardless. :)

Thanks for the mesolite tip. I found a document that says that mesolite doesn't clean well in anything water-based, as the fibers tend to clump up afterwards (like wet hair), and recommends (among other things) alcohol. So I'll give that a try.

[margaretB]

Thanks for the information. It was really a great thing to find science. As this crystal was formed and were beautiful.

[Rei]

Time for an update to this thread

Found a couple more zeolites while climbing waterfalls on the Fossá, a place I'd not been before. Guess that changes my "you don't find anything neat at waterfalls" atttitude ;) Like before, they were in eroding "mud". These aren't as impressive as the previous finds, however, so I haven't photographed them.

I did some additional investigations into the previous sample. First, I tested for reactivity with HCl.

* I could hear and kind of see a reaction with the druse, but it wasn't very fast.
* I don't think I heard a reaction with the fibrous material or its substrate

I then broke off a tiny crystal or two from the druse and a tiny chunk of the fibrous material and added them to a plastic container filled with a bit of 30% HCl. Again, I noticed an immediate reaction with the drusy crystals, but nothing obvious with the fibrous material - although there could have been something slow. The next time I checked back, the HCl had turned bright urine-yellow, a pretty impressive color change I'd say given that the HCl outmassed the crystals by 2-3 orders of magnitude. I don't know what material changed the color, but I'm guessing the druse. I left it in there for 1-2 weeks just to be sure any action was done. I was surprised that both minerals were still visibly present, though the drusy material looked smaller. I did some tests (below) pressing on them with a nail. The fibrous material was still quite firm and did not damage, but the drusy material shattered into little crystals with very little force. Nonetheless, they were still solid.

I diluted the HCl to irrelevance and placed both on a microscope slide. The drusy material held together by water surface tension and was hard to separate, but I managed to separate it enough to view. You can see a photograph below - there's both cracked platy crystals and small crystalline fibrous bundles. The bulk fibrous material that had little visible reaction with the acid was too thick to photograph via transmission microscopy, and in my attempt to do reflection microscopy, I accidentally shattered my only really bright light bulb in the house :Þ

Thoughts?

[Mike Wood]

Hello Rei, thanks for the update. I can't tell you anything different from what I said earlier - I still think the platy crystals are stilbite (or barrerite, like Jordi said) and the fibrous material could be 'mesolite'. The discolouration of the hydrochloric acid is most likely due to iron leaching from the tiny bit of dark material from the edge of the druse, forming iron (II) chloride.

Mike

[Rei]

Thanks a bunch, Mike :)