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diddi
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Well I have started a very small scale examination of Lazurite (Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)]. it is the blue mineral in Lapis Lazuli. It is a
cyclosilicate with S3- ions responsible for the distinctive blue colour.
Small whole pieces have been added to NHO3, HCl, H2SO4 and NaOH with the following observations after 5 days.
All 3 acids are capable of decolourising the material, with nitric acid acting the fastest.
Whilst small bubbles are slowly evolved from each, Sulfuric acid was most noticeable with bubbles surrounding the stone in a couple of hours
All acid samples have resulted in a collapse of the solid structure of the stones into a gritty mush. none of the samples have been agitated.
The NaOH has no effect on lazurite at all. more to follow, and maybe even a proper write up if anything interesting happens
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aga
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Cool !
"We're not just bashing rocks together here .."
- we're dissolving them in acid !
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diddi
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Further to the lazurite observations:
After about 10 days there has been an interesting turn of events.
Of the 3 acids, only the dilute (about 5M) H2SO4 has had any further activity. The material has almost completely dissolved to a very fine grit which
when swirled takes an hour or so to settle. The particulate matter is white and there is no evidence of the blue colour. what is interesting to note
is that an amount of black/gold grit has appeared which is considerably denser than the white solid. under microscope I confirmed that the grit is
tiny pyrite cubes, barely .1mm across!
So I am now at the stage where I will do a quantitative analysis using H2SO4 to determine the mass of solids remaining after digestion of the
lazulite. any suggestions welcome
[Edited on 7-8-2015 by diddi]
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aga
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Get on with it !
People tend to prefer to criticise before they Enlighten.
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The Volatile Chemist
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I just cleaned a geode with 100mL HCl. Maybe later I'll provide before and after. It had a calcite inclusion, which made washing it tedious, but it
worked for the part I could immerse without ruining the inclusion. 18-pounder, the bigger half was upon breaking.
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aga
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What ?
You're rubbing it with HCl ?!?!
Why ? (Fetishes are allowed.)
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j_sum1
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I have a few rocks in storage that I might have a go at. Interestingly, in doing a quick wikipedia search I found a photo of the location where I got
them from: https://en.wikipedia.org/wiki/File:Multi-coloured_scoria_in_...
My intention was to make a chess set from different coloured rocks that I collected from the crater of Mt Tarawera.
https://en.wikipedia.org/wiki/Mount_Tarawera The crater is a rift 16km long.
Anyway, I have samples of both red scoria and black scoria and also some white rock that I believe is ignimbrite. I rather expect the scoria samples
to be unfruitful -- very dense and containing a lot of silicates. I wouldn't be surprised if the ignimbrite throws up some interesting things though.
It will probably be at least a week before I get to these however. I'll do some local rock and soil at the same time.
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diddi
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@TVC - where is your geode from?
@j_sum - wow the white one almost looks like pumice, but whiter. I bet it would have beaut microstructure
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j_sum1
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My white rocks are different from that one. They are quite different from the scoria. They are not porous, have no gas bubbles and are relatively
soft -- almost chalky. Quite large sparlky crystals are visible in the right light -- maybe greater than 0.5mm. I will have to dig them out and have
another look soon. When I do, I will take photos.
Oh. I do have some scoria pieces that were cut into thin strips using a tile-saw. Might be good for a look under a microscope. I can send you some
if you are interested.
J.
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The Volatile Chemist
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My geode is from southern Indiana. I rubbed it in HCl to clean the rust and dirt from the interior. Looks great, except now there's ferric chloride on
the outside of the rock 
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Texium
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I have a whole bunch of thundereggs ranging from grape size to softball size that I dug up with my cousins in eastern Oregon a few years ago. I've
considered trying to clean some of them up, but I'm not sure how exactly to go about it, and I'm nervous about possibly damaging them.
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aga
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Thundereggs ?
Do what ?
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j_sum1
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thundereggs = geodes
https://en.wikipedia.org/wiki/Geode
https://www.google.com.au/search?q=geodes&safe=strict&am...
[Edited on 12-8-2015 by j_sum1]
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Texium
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Not exactly https://en.wikipedia.org/wiki/Thunderegg
Although I'm not 100% sure what the difference is. Maybe that thundereggs are usually not hollow?
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j_sum1
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I thought they were synonyms.
It seems that that particular wiki article is splitting hairs on the definition but lacks the language precision to make matters clear.
Quote:
Thundereggs are found globally wherever conditions are right. /quote
Well, duh!
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Texium
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Yeah, it's certainly not a great article. But if you look at pictures of thundereggs compared to pictures of normal geodes, geodes seem to usually be
hollow and contain well defined crystals, while thundereggs are generally solid and less "crystally," which is how I expect mine to be inside, so I
guess that's the difference.
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diddi
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no difference. geode is the more geologically accepted name. thunderegg is likely a trade/invented name. they have nothing to do with thunder. they
are volcanic
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Texium
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Quote: Originally posted by diddi  | | no difference. geode is the more geologically accepted name. thunderegg is likely a trade/invented name. they have nothing to do with thunder. they
are volcanic |
Yeah, it's a Native American mythological thing. But there definitely seems to be some
distinction if you compare pictures of them. Just google thunderegg in one window and geode in another and look at them side by side.
Perhaps thundereggs are all geodes, but not all geodes are thundereggs?
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diddi
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there is no difference. but geodes from different locations are very different, so if all the geodes collected in 1 are get colloquially known as
thundreggs, then you think they are differently named.
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The Volatile Chemist
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Perhaps a linguistics subforum is necessary?  
The HCl cleaned mine up very well, just be sure to rinse it out thuroughly before letting it dry.
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diddi
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any aussies molesting a rock atm? I just received some interesting ores from Tennant Creek. Possible Ni, Fe, Cu, As, Co? not that sure yet. I
emailed the local gemstone club and they kindly did not reply, so no formal ID yet.
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j_sum1
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Nice Diddi. No molestin happenen here. Got my plate full of other things.
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diddi
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re cleaning geodes (and others):
I have a pressure washer which is marvellous for prepping minerals etc. I lock the water on and then hold the specimen in the stream at a distance
that suits the ferocity of cleaning I need. the results are great. HCl does not remove staining generally, only lose stuff anyway (or it burns out
calcites etc that you did not pay attention to). anyway just food for thought 
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The Volatile Chemist
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Yeah, I almost dissolved some carbonate out of a geode, but luckily noticed when the bubbling started.
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diddi
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easy to do. I don't use acids for washing at all.
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