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12AX7
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Can you take any bigger photos or zooms of the texture of the dark stuff?
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Eddygp
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Yes. I will attach them to this post. I advance that tiny transparent crystals are within this dark massive mineral (iron-impurity vaterite? don't
think so, too rare  ) and those might be the clue to find out what this really
is.
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bfesser
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Did you forget?
Anyway, that's a damn interesting specimen. Could you describe the geology of the area or even the formation where you found it?
[edit]I keep forgetting to ask: Is it limestone or dolostone? An acid test with dil. HCl would differentiate the two.
[Edited on 8.9.13 by bfesser]
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Eddygp
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I did forget, sorry. The rock dissolves even in acetic acid, so I suppose that it will dissolve in HCl too. So well, I've attached the photo here
instead. Hope it's useful. Regarding the place, it is a sedimentary rock area near a K-T clay deposit. The soil is mostly clay, in a warm-to-hot, dry
area.
EDIT: That photograph is apparently the most interesting part of this rock, as you can see the transparent crystals and the barrier between the
coloured and white parts of the specimen.
[Edited on 8-9-2013 by Eddygp]
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bfesser
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Don't you have HCl to do tests with? The photo's not as useful as I'd hoped (compression & lighting), but it's still neat. Thanks for uploading
it. Forgive my ignorance, but I've never heard of "K-T clay." Are you referring to what used to be called the <a
href="http://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_boundary" target="_blank">K–T boundary</a> <img
src="../scipics/_wiki.png" />, by chance?
Also, if you don't mind (anonymity), could you provide a specific location for where you collected the specimen? It's difficult to impossible to do
amateur arm-chair geology without knowing where exactly virtual specimens are from. Without knowing the geology of the area, it's like playing a game
of <a href="http://en.wikipedia.org/wiki/Twenty_Questions" target="_blank">Twenty Questions</a> <img src="../scipics/_wiki.png"
/>...
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Eddygp
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Quote: Originally posted by bfesser  | Don't you have HCl to do tests with? The photo's not as useful as I'd hoped (compression & lighting), but it's still neat. Thanks for uploading
it. Forgive my ignorance, but I've never heard of "K-T clay." Are you referring to what used to be called the <a
href="http://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_boundary" target="_blank">K–T boundary</a> <img
src="../scipics/_wiki.png" />, by chance?
Also, if you don't mind (anonymity), could you provide a specific location for where you collected the specimen? It's difficult to impossible to do
amateur arm-chair geology without knowing where exactly virtual specimens are from. Without knowing the geology of the area, it's like playing a game
of <a href="http://en.wikipedia.org/wiki/Twenty_Questions" target="_blank">Twenty Questions</a> <img src="../scipics/_wiki.png"
/>... |
Yes, I was referring to the K-T boundary, a clay deposit from that time (according to some webpages). Sorry for the mix up. I'll send you a PM with
the Mindat location.
there may be bugs in gfind
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Eddygp
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Mini-bump. Not really a bump, just a mini-bump.
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bfesser
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Sorry, I've been busy with other projects. Have you made any progress on the chemical tests or to determine the suspended solid?
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Eddygp
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When reacting with HCl, it becomes orange in solution (probably Fe ions?) and effervesces totally. Actually, there is a light brown precipitate, so
maybe the colour is not just in solution. Nothing unexpected. I will edit this post if there are any new things going on after a while.
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Eddygp
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Changes:
The precipitate has completely settled down. There is a fine suspension of this precipitate in the solution, but apart from that, the solution's
colour is just off-white, not creamy though, just a little coloured. This might be because of a different impurity.
Fe2O3 is highly soluble (reacts) in HCl, so the ppt. is not iron(III) oxide. However, what else might it be, a light brown to
orange-ish ppt. which is insoluble in HCl? I do not have any flocculants available so I cannot get the suspension to settle at the bottom. However,
the nature of this ppt. is highly intriguing. Any guesses?
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12AX7
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What pH are we talking? Fe(OH)3 drops out above 3 or so; it's quite acidic itself. It also dissolves slowly if it's much bigger than colloidial.
Drop in a whole bunch more, give it more calcite to suck on? Then see if anything drops out from the raised pH?
Tim
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Eddygp
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Well I added 21% HCl in this beaker with about 1.2 grams of the mineral, so... well.
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Eddygp
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Observation after 4 days:
All the impurities have precipitated off solution giving a colourless solution and a powdery orange (not brownish, pure orange) precipitate. I've no
idea... what is it? I'll read up a bit on transition metals' oxides and halides to see what it is.
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12AX7
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Cu2O and Fe(OH)3 would fit the bill; can't think of any others? (V2O5 maybe, but that obviously would behave differently. And Cu2O itself would at
least partly oxidize in solution, giving something green-stained, not orange.)
Tim
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bfesser
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Cu<sub>2</sub>O is red, not orange. I agree that it's likely an iron oxide, hydroxide, or oxide/hydroxide. Determining exactly which
might prove difficult.
<a href="https://en.wikipedia.org/wiki/Iron_hydroxide" target="_blank">Iron oxide</a> <img src="../scipics/_wiki.png" />
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Eddygp
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| Quote: Originally posted by bfesser | Cu<sub>2</sub>O is red, not orange. I agree that it's likely an iron oxide, hydroxide, or oxide/hydroxide. Determining exactly which
might prove difficult.
<a href="https://en.wikipedia.org/wiki/Iron_hydroxide" target="_blank">Iron oxide</a> <img src="../scipics/_wiki.png" />
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These would dissolve in the HCl, AFAIK.
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12AX7
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Actually it can be as bright as yellow -- this is seen electrolyzing a copper anode in a concentrated NaCl solution. Initially, nearly colloidial
Cu2O precipitates, with a refreshingly yellow to golden color (there's probably some "quantum dot" action at work). So it depends on precipitation
method and rate: the classic method with Fehling's solution yields a dull brick red, for example. But I don't think normal precipitation methods
(i.e., quenching a Cu(I) solution in base) yield anything brighter than dull orange, so you are right for the most part.
Tim
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Eddygp
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Cu oxides would also dissolve in acid.
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Eddygp
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Reason for the necroing: I have found iron minerals (not trace impurities, minerals by themselves) from the exact same area.
They are reddish brown with orange tinges and when dissolved in HCl, they form a yellow solution, indicating Fe (unless I have found an awesome mining
site, which I don't think so). Their crystal habit is massive. They are (locally) very common.
Here is the problem. I looked at possible iron oxide minerals and saw a possible candidate: maghemite. However, maghemite is strongly ferromagnetic and this mineral... was not. Actually, it probably is diamagnetic.
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Eddygp
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EDIT: similar massive formations of this mineral have been sighted attached to large sedimentary rocks (calcium carbonate and other calcium rocks).
Brownish to dark orangeish, just like rust (couldn't edit, doubleposting, read last post for this to make sense), which led me to
think about that mineral. Locally very common.
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bfesser
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| Quote: Originally posted by Eddygp | | Reason for the necroing: I have found iron minerals (not trace impurities, minerals by themselves) from the exact same area. |
Have you collected any specimens? Also, photos of both the specimens and the outcrops where they've been collected from would be
great.
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Eddygp
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Photos 1&2. THIRD attempt to post.
In a RAR.
Attachment: MineralPhotos1.rar (1.8MB)
This file has been downloaded 269 times
[Edited on 9-2-2014 by Eddygp]
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Eddygp
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Photos 3&4.
In a RAR.
The fifth photo is too large to upload. I'll crop it within the next few hours.
Attachment: MineralPhotos2.rar (1.5MB)
This file has been downloaded 294 times
[Edited on 9-2-2014 by Eddygp]
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Eddygp
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The photos are available in this science madness FTP server.
http://www.scimad.org/users/Eddygp/Agost%20047.JPG
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<a href="http://www.scimad.org/users/Eddygp/Agost%20018.JPG" target="_blank"><img
src="http://www.scimad.org/users/Eddygp/Agost%20018.JPG" width="250" /></a> <a href="http://www.scimad.org/users/Eddygp/Agost%20021.JPG"
target="_blank"><img src="http://www.scimad.org/users/Eddygp/Agost%20021.JPG" width="250" /></a>
<a
href="http://www.scimad.org/users/Eddygp/Agost%20028.JPG" target="_blank"><img src="http://www.scimad.org/users/Eddygp/Agost%20028.JPG"
width="250" /></a> <a href="http://www.scimad.org/users/Eddygp/Agost%20032.JPG" target="_blank"><img
src="http://www.scimad.org/users/Eddygp/Agost%20032.JPG" width="250" /></a> <a href="http://www.scimad.org/users/Eddygp/Agost%20047.JPG"
target="_blank"><img src="http://www.scimad.org/users/Eddygp/Agost%20047.JPG" width="250" /></a>
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