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Mysterious Black Crystals (Something Fishy!)
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Pete Richards
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PostPosted: Mar 20, 2015 16:17    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

Andy, you mentioned pyrite, but we have not seen a good picture of it. I think I see a few glints that might be it in some of your images.

Can you get a reasonably close-up picture of the pyrite?

In this environment, pyrite should not precipitate if, as you suggest, the interface layer where these pyrite grains were found was aerobic. And if pyrite formed anywhere in the "sediment", it should have been a black mud, and in fact probably FeS and not pyrite, FeS2. There is a lot of evidence of specialized bacteria precipitating iron sulfides as part of their metabolism, but not as shiny yellow-colored grains that a mineralogist or once-potential geologist would recognize by eye as pyrite.

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PostPosted: Mar 22, 2015 01:12    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

In one of the magnified pictures (40x) I see clearly a cleavage as it is typical for micas.
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PostPosted: Mar 25, 2015 09:16    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

Just popping in to assure you all that I haven't abandoned you!

I'm awaiting replies to e-mails that just may shed some further light. Amongst that burst of communications, I made enquiries about XRD services in the UK, though I'm not terribly hopeful that any that do reply will be economically feasible. I'm most grateful to Alfredo for his suggestion and may well finish up adopting it.

In the meantime, I've made another observation and will return with news of that if-and-when I've convinced myself that it's real.

To keep you going, here are some comments re the pyrites ...

I noticed them when I passed some substrate through a kitchen sieve into a bowl of water in order to separate out some of the larger black crystals. The effect was one (if you'll pardon the expression) of a golden shower raining down into the bowl.

Pic#1 is of a brine shrimp sieve that I put in the path of what was coming through the kitchen sieve. Pic#2 shows a group of larger pyrite fragments.

The fragments are formed of thin sheets that broke apart easily (and annoyingly) when tweezered onto the surface I used to photograph them for you.

It may be useful for us to bear in mind that this phenomenon occurred in an environment where some/most/all surfaces are covered with a biofilm. As demonstrated to me in a different exercise, conditions locally within a biofilm may cause unexpected things to happen. That may, or may not, be relevant here but I thought I'd just mention it.

More news as I get it ...



GoldenShowers.jpg
 Mineral: Pyrite
 Description:
Milton Keynes
1-2mm
Some of the pyrites as separated from the substrate.
 Viewed:  48160 Time(s)

GoldenShowers.jpg



Ptrites Crystals_2.jpg
 Mineral: Pyrite
 Description:
Milton Keynes
c2mm
Pyrite crystals isolated from the substrate.
 Viewed:  48246 Time(s)

Ptrites Crystals_2.jpg


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PostPosted: Mar 25, 2015 10:41    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

Dear Andy,

Although your fragments look shiny, I think I can guarantee you that they are indeed MICA, not pyrite. I'm sure the others from the Forum who may reply, will agree with this. You can confirm it by jabbing one with the point of a pin or needle; they will be soft, get indented, and the flake will tend to split apart. Pyrite, on the other hand, is hard and brittle--there would be no mark or indentation, unless you crunched it so hard as to break the pyrite grain (which would probably bend the point of a needle, too).

And this mica, must definitely have been a component of the sand or gravel--NOT something that could have formed in your tank!

Cheers, Pete
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PostPosted: Mar 25, 2015 13:33    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

Looks like mica to me
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PostPosted: Mar 25, 2015 14:51    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

P.S., Andy, as opposed to being "regular mica", these might also be pieces of vermiculite (a type of mica), such as is used in packing material, potting soil, absorbent for liquids, etc.
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PostPosted: Apr 10, 2015 06:22    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

I'm still here and still busy gathering data for you to evaluate.

I contacted a range of lab services here in the UK that purported to offer XRD. One or two of them in fact don't (despite what Google claimed) ; others were just too expensive for me ; a couple didn't reply in within my patience time-frame!

So I took up Alfredo's suggestion and sent samples to John Attard. Sod's Law dictated that as soon as I had done that, one of the non-respondents would reply. In fact it was barely a couple of hours after I'd returned from the Post Office that a lab in one of the London Colleges offered to do XRD for free - so long as there was no commercial gain to be had ; and so long as I was prepared to wait since they are very busy. I have now sent the samples off to London.

In the meantime, John Attard phoned (yesterday) to say he'd received the samples and to collect my payment details. His results came back less than an hour later!

I'm uncertain as to whether I can copy the results to here without catastrophically contravening the forum posting rules for attachments, so I won't do that without express permission. Briefly, though : the larger black crystals are estimated to be edenite/magnesiohornblende ; and the tiny gold flakes to be 'mainly' phlogopite mica.


Through diligent rummaging for info of a family nature, I came across an old hard disk drive which (it turned out) contained text and images recorded as I was setting up this aquarium. I can confirm with 95% confidence that I didn't, either then or subsequently, add either of these two materials to the tank. I'm reserving the 5% because I see that I added a little plant-growth medium underneath the sand : it doesn't appear to contain either substance (it would be obvious) but I need to be sure, so I'm doing some checks with its producer. I see also that there was some silicone sealant used to stick bits of the aquarium's décor together - but I'm disregarding that for the time being because ...


... Suspicions are clearly now focussing on the proprietary aquarium gravel that I used.

I'm in conversation with its manufacturer and am learning about its production. Apparently the basis for it is mined in Bavaria. The quartz crystals that come out of the ground are (they say) associated with a certain amount of feldspar ; maybe there's other stuff, too. The material is size-graded and the resulting correctly-sized grains are coated with resin, 'natural' colouring and iron oxide. I have asked for a sample of the grains as they are before they receive these coatings and have just had a reply to say they're sending me some. I'll report back when it arrives.


Something that disturbed me just a little as I was gathering samples to send to London was the discovery of a (relatively) humungous black crystal : much larger than the 'average' size of them ; and much larger than any of the grains of gravel. Hmmm.


Anyway, that's my update for now. I haven't forgotten the questions (up-thread) about minerals in the water and about pH regulation and will return to them in due course if-and-when it seems appropriate.

Thanks for your continued attentions.
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PostPosted: Apr 29, 2015 08:25    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

Hi Everyone

I'm still making progress, albeit rather slowly. Since many of the photographs that I need to illustrate my story don't 'fit' here, I'm collating them on the fishkeeping forum which I inhabit and will link you to it when I'm done. There you will eventually find further details of water chemistry etc.

At the moment. though, I have an issue on which I'd appreciate some advice, if you'd be so kind.

The attached photograph depicts the material that is later given coatings to produce the relevant aquarium gravel. Although everything is coloured some shade of grey or white, a fraction of the grains are clearly whiter than the rest ; others I'm not so sure about.

As you can see, I've tweezered-out grains that are very obviously much whiter than the rest : I'm reliably informed that these latter grains are feldspar.

I would like to optimise my feldspar-tweezering-out ability (I'm not going mad - I have a specific reason for doing so!). So is there any tip or trick that you can pass on to me to help me extract as much of the feldspar as possible from a measured sample of gravel?

I have 445 gams of the 'raw' gravel to play with, by the way.



NaturalBase.JPG
 Mineral: Quartz and Feldspar
 Dimensions: 1-2mm
 Description:
The raw material from which the aquarium substrate is manufactured.
 Viewed:  43828 Time(s)

NaturalBase.JPG


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PostPosted: May 10, 2015 06:32    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

I'll take that as a 'no', then?

I did have a bash at this, using the resources at my disposal. My most successful effort (not that that is saying much!) was the construction of a light box into which I put a uV lamp (368nm). 'Feldspar' crystals laid on top appeared opaque ; quartz crystals laid on top appeared transluscent.

The trouble was that the quartz crystals that I could see under white light having a partial coating of 'feldspar' appeared opaque, too, under uV. (I think I can just about stay within the forum's rules if I post a pic of the result.)

So I had to abandon that as a reliable method of efficient separation. Unless a different method can be suggested, I will therefore not be able to produce an estimate of how much 'feldspar' may have been present in the original substrate.

I am in process of trying to have the identity of the 'feldspar' crystals confirmed.

The 'London' XRD analysis on the black and golden crystals came through, agreeing substantially with John Attard's : the former as 'an amphibole of the hornblende family' ; and the latter as 'fluorophlogopite' mica.

I hope to be able to persuade someone to use a polarising microscope on the black crystals with a view to reducing the number of possibilities as to which species they could be.

I have a picture (I cannot publish it here I guess without special permission) which appears to support my hypothesis that the black crystals did form in the aquarium.

More news as I get it ... perhaps. I may be being over-sensitive, but does the non-response to my last indicate that this community would rather I didn't post any further on this subject?



uV.JPG
 Mineral: Quartz and Feldspar
 Description:
Bavaria
1-2mm
Grains of quartz and feldspar suspended over a 368nm uV light.
 Viewed:  42677 Time(s)

uV.JPG


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PostPosted: May 10, 2015 07:13    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

Andy, you were using a longwave UV light. If you get a shortwave UV light, and hang it OVER the sand, so you can see the sand by reflected light instead of transmitted light, in a dark room, you will be more rapidly able to separate the feldspar sand from quartz sand grains, because most feldspar grains emit a dull red fluorescence under these conditions, whereas quartz does not. Wear goggles and gloves, because SW UV can rapidly cause sunburn.
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PostPosted: May 10, 2015 07:16    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

If the analysis says that the black crystals are edenite, then they're edenite.

Yes, edenite is found in Bavaria:

https://www.mindat.org/min-1351.html

No, edenite does not form in water (under anything remotely near STP conditions). It requires significant heat (hundreds of degrees celcius) to form. It is not a precipitate of aqueous solutions. You're just as likely to have diamonds and emeralds start precipitating out in your tank as a hornblende mineral.

I'm not sure why you're still researching this now that you got test results back. Twice. Saying the same thing.
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PostPosted: May 10, 2015 09:34    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

alfredo wrote:
...If you get a shortwave UV light, ... Wear goggles and gloves, because SW UV can rapidly cause sunburn.


Thank you, Alfredo. I feel somewhat chuffed because I was (more by luck than by good judgement, perhaps) on vaguely the right track!

After Googling, I see that I can get a 152nm uV bulb that will fit my little hand-held lamp, for £7.56 ; the supplier says that they can't ship until 9th June, so I've got a little time yet to decide whether it would be worth the money.

My further difficulty lies in estimating with reasonable reliability the amount (in terms of volume and/or weight) of 'feldspar' that is actually attached to a proportion of the quartz grains. At the moment I can't see a way around that.

Anyway, thanks again for another helpful suggestion (and for the health & safety warning).
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PostPosted: May 10, 2015 09:39    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

Rei wrote:
I'm not sure why you're still researching this now that you got test results back. Twice. Saying the same thing.



I am continuing to pursue this matter principally because what I'm being told by mineralogists does not seem to match up with my observations and I'm seeking an explanation that will satisfy my curiosity. I'm also learning something about mineralogy along the way (which I'm rather liking!).

Consider :

The black crystals were not present in the raw material from which the aquarium gravel was manufactured : fact.

The black crystals were not present in or among the gravel grains subsequent to manufacture : fact.

I did not introduce the black crystals to the aquarium gravel before it was added to the aquarium, or before the aquarium was commissioned : fact.

The black crystals were not present in the planting medium that underlaid the aquarium gravel : fact.

I did not add the black crystals myself to the aquarium during its lifetime : fact.


... and yet they are there. Where, then, did they come from?


To be clear : I don't dispute the conclusion that they match to known properties of edenite/magnesiohornblende (et al.) via analysis. However, on the face of it something appears to be awry with the assertion that this material could not possibly have formed in my aquarium.

I will therefore continue to pursue the problem and, generally speaking, I choose not be diverted by brusqueness or derailed by implications of contrariness. However, sensing some hostility here, I will desist from posting further until a Moderator gives me the 'all clear'. I trust that satisfies you, Rei?
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PostPosted: May 10, 2015 19:08    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

Hello Andy,

Though I am a moderator on this forum, I am writing this response as myself, an individual. I have Master's Degree level training in mineralogy, and have studied minerals for 35 years post PhD. That does not mean that I know everything, but it does at least indicate that I have been introduced to current thinking from many professional mineralogists and petrologists.

You express some frustration that you have not heard more from us, and some sense that your posts are no longer welcome. I will say that I have found this an interesting thread, exactly because of your tenacity in pursuing your mystery and your ideas about how to understand it. You have done a lot of work and spent some money seeking answers. At the same time, this thread is frustrating because many of us are telling you that your hypotheses about minerals forming in your fish tank are totally in conflict with the large body of knowledge about the conditions in which specific minerals form (or are altered into others such as clay minerals). And, having formed your hypothesis, your are determined to prove it.

The best science forms hypotheses, and then improves their credibility by trying to prove them false. Scientists are often unpopular people, because our first response is always "How do you know?!!!"

You have had two determinations that your dark mineral is an amphibole of the hornblende group. It really does not matter exactly what its chemical composition is (which will determine whether it is edenite, fluorrichterite, hornblende, or some other species). All of these minerals form at temperatures of about 550° C to 800° C and pressures corresponding to being buried in the earth at depths of 7.5 to 50 kilometers. Not your typical fish tank environment! This information is based on numerous experiments where rock-forming elements have been sealed in inert containers and heated to specific temperatures and pressures to see what minerals would form. You can search the web for "amphibole phase diagrams" and find the ones I am referencing here (along with many that are irrelevant for this topic).

You propose several "facts" to support your case:

"The black crystals were not present in the raw material from which the aquarium gravel was manufactured : fact."
Or perhaps they like all of the other grains were coated with a white coat to make them appear homogeneous. That is the way my aquarium gravel appears to be prepared.

"The black crystals were not present in or among the gravel grains subsequent to manufacture : fact."
This is essentially the same assertion. It hangs on whether you really saw what was inside the white gravel, and what the manufacturer chose to tell you about their possibly quite proprietary raw material.

"I did not introduce the black crystals to the aquarium gravel before it was added to the aquarium, or before the aquarium was commissioned : fact."
I believe this. But it provides no evidence that they grew in the gravel as you assert, unless it can be shown that you DID introduce them and they have grown larger.

"The black crystals were not present in the planting medium that underlaid the aquarium gravel : fact."
Possibly true, and probably true based on the medium's function, but you have done little to address this question, based on the posts I have seen. So it is an unevaluatable assertion.

So where are we? You have a "remarkable" observation of a hornblende mineral growing in your fish tank, and attribute it to something going on in your tank. The huge body of experimental petrology indicates that this is impossible. How can you proceed? I think spending time/money on identifying the particular amphibole species is a waste - it will gain you nothing.

If you really believe your fish tank grows amphiobles and micas, do some further controlled experiments. Get fish gravel from several sources (perhaps including local stream gravel, screened to the right size and sterilized). Make epoxy-embedded mounts of each source, and have thin sections made (for a cost) to see what minerals are really in there. Set up tanks innoculated with the same water and with each source gravel, and run them for however many months or years (another variable). Then wash the gravel, make new epoxy mounts, and see if you can document statistically that the amount of amphibole or mica has increased over this time. Can a replicate tank produce amphiboles? Do other tanks also do so?

If you can provide this experimental evidence, we might take you more seriously. But for the moment you appear to be someone who has an interesting but unplausible hypothesis that the body of scientific evidence does not support, but that you are determined to advance.

The length of the message will convey, I hope, that I am not hostile to your postings, but that I think you are barking up a non-existing tree, and are rather stubbornly refusing to accept indications of that fact.

Until you provide much more substantial experimental and observational reports, I will not respond further.

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PostPosted: May 11, 2015 09:10    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

Thank you, Pete, for your considered reply. I understand your stance with respect to the status quo and/or your knowledge-peers ; nevertheless I cannot at this time bring myself to accept it. The possibility strongly seems to exist that I may have stumbled upon something quite unexpected. I know that, as you said, you won't respond to the following ; but anyway ...

The only doubt you raised was the one of whether or not the manufacturer of the substrate was being mendacious for reasons of commercial interest. It's not something that had occurred to my trusting nature, so thanks for that. I shall of course check this out so far as I am able.

I'm not going to waste any more of your, or threadmates' time here. However in the, (unlikely, I know!) event that anyone would like to follow any progress that I might make - maybe also to offer further guidance - I invite them to PM me and I will provide contact details. Prior to de-registering (etc.) I will remain a Member, if allowed, for 48 hours to allow time for this to happen.

Otherwise I would genuinely like to thank you all for your attentions and wish everyone all the best.


A final allegorical offering (perhaps not perfect but at least it's contemporary!) ...

6mA. Who knew, eh? ;-)
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PostPosted: May 11, 2015 14:53    Post subject: Re: Mysterious Black Crystals (Something Fishy!)  

I'm quite a fan of 'the simple explanation', generally speaking, as an answer to a lot of life's problems. Maybe someone dropped some 'gravel' in your aquarium for a joke... Have you considered foul play? It would make much more sense to me. (Not joking!)
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