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What is embedded in this ancient reef rock?
  
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Coral




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PostPosted: Jul 24, 2019 02:58    Post subject: What is embedded in this ancient reef rock?  

I don't know much about minerals, my hobby is actually saltwater fish tanks and collecting corals. For new aquariums we sometimes use dry harvested from land ancient reef rock made up of calcium carbonate; limestone. This rock comes from ancient reef when the Florida landmass was formed, you can sometimes see fragments of shells in these rocks.

I happened to get a piece which has a dark colored rock or metal embedded in it. I realized it was in there about a week after putting it inside my newly filled aquarium and I got nervous because most heavy metals in the water will kill corals. I called the place I bought the calcium carbonate limestone rocks from and also another reputable vendor who have both gone through tons and tons of these rocks but never seen anything like this before.

Typically the rocks are just whiteish porous limestone. I posted a pic in one of the fish forums Iím part of and someone said maybe itís a meteorite that;hit the ancient reef, which never crossed my mind. My mind tends to go to bad things, like uranium, which I see in google can be in limestone sometimes. Again, Iím completely ignorant and have no idea what this could be.

Anybody have any idea what this is or how to find out? The surface area is maybe the size of a dime. One picture shows the entire limestone rock in my aquarium, with the small piece Iím questioning towards the top. The other pics that are actually clear were taken in the sunlight when I pulled the rock out and itís still wet.



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alanbartlett




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PostPosted: Jul 24, 2019 03:49    Post subject: Re: What is embedded in this ancient reef rock?  

Without wishing to be frivolous and having no idea what it may be - I have to say, in the second picture particularly, it looks for all the world like a puppy dogs head, complete with ears, eyes and a nose!

Sorry!
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Bob Harman




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PostPosted: Jul 24, 2019 05:50    Post subject: Re: What is embedded in this ancient reef rock?  

First of all I very very much doubt the piece you note has anything to do with a meteorite.

Coral reefs, made up largely of CaCO3...limestone, as you note.....are formed in shallow waters. Lots of material, nos, becomes included into the growing reef coral due to multiple causes such as wave action during storms. Other actions such as floating dead logs with bits of rock in their roots might contribute as the rock chips break off and fall into the growing corals. Even bits of passing ships might be possible, if the coral is quite recent. You probably have found one of these non-specific inclusions.

If very curious, you could etch away the limestone with vinegar or muriatic acid to see if the inclusion remains behind, but I would not bother. You can rest assured that small inclusions like you have found pose very little risk to the tangs, clownfish etc etc in the tanks.

BTW, my former hobby was tropical fish. I had several very large 130 gal tanks. One had a fresh water Arawana; bought it at 4" then it grew to 16" and jumped out of the covered (!) tank onto the floor. Very powerful, I replaced it and had to put a brick on top of the cover. I guess the strips of beef heart that I had fed it really were nutritious! BOB
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Kevin Schofield




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PostPosted: Jul 24, 2019 09:25    Post subject: Re: What is embedded in this ancient reef rock?  

I think this is most likely to be a small nodule of chert...which is to say a small volume of the limestone that has been replaced by silica. The detail photographs, although a little fuzzy when blown up, do seem to show that the black fragment is porous and somewhat "intergrown" with the limestone (for example at the bottom of the black nodule). Both of those characteristics would be consistent with it being a chert nodule "arrested" in growth, having had only enough silica in solution to partly replace the limestone matrix.

If this idea is correct, it should be very hard (won't scratch with a steel knife blade), and very definitely will do no harm to the denizens of your tank!

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PostPosted: Jul 24, 2019 10:48    Post subject: Re: What is embedded in this ancient reef rock?  

As Kevin notes, hard to tell from the images, but the thing does look porous, with "bubbles" that are more than half-spheres. This would rule out a meteorite since ablation surfaces tend to be scoop shaped instead of spherical

You could also test it with a magnet to see if it contains iron

Another possibility is a small piece of pumice...these can float long distances before becoming waterlogged...and there are plenty of volcanoes in the Caribbean that have pumped out pumice over the last 40 million years

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Coral




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PostPosted: Jul 24, 2019 10:53    Post subject: Re: What is embedded in this ancient reef rock?  

Bob Harman wrote:
First of all I very very much doubt the piece you note has anything to do with a meteorite.

Coral reefs, made up largely of CaCO3...limestone, as you note.....are formed in shallow waters. Lots of material, nos, becomes included into the growing reef coral due to multiple causes such as wave action during storms. Other actions such as floating dead logs with bits of rock in their roots might contribute as the rock chips break off and fall into the growing corals. Even bits of passing ships might be possible, if the coral is quite recent. You probably have found one of these non-specific inclusions.

If very curious, you could etch away the limestone with vinegar or muriatic acid to see if the inclusion remains behind, but I would not bother. You can rest assured that small inclusions like you have found pose very little risk to the tangs, clownfish etc etc in the tanks.

BTW, my former hobby was tropical fish. I had several very large 130 gal tanks. One had a fresh water Arawana; bought it at 4" then it grew to 16" and jumped out of the covered (!) tank onto the floor. Very powerful, I replaced it and had to put a brick on top of the cover. I guess the strips of beef heart that I had fed it really were nutritious! BOB

These calcium carbonate rocks are harvested from fairly deep down I believe. Iím not worried about the fish, they would be fine, itís the acropora coral I like to grow. If there is heavy metals in the tank they die. I hope you found that big Arawana on the floor before it was too late!
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Coral




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PostPosted: Jul 24, 2019 11:02    Post subject: Re: What is embedded in this ancient reef rock?  

Kevin Schofield wrote:
I think this is most likely to be a small nodule of chert...which is to say a small volume of the limestone that has been replaced by silica. The detail photographs, although a little fuzzy when blown up, do seem to show that the black fragment is porous and somewhat "intergrown" with the limestone (for example at the bottom of the black nodule). Both of those characteristics would be consistent with it being a chert nodule "arrested" in growth, having had only enough silica in solution to partly replace the limestone matrix.

If this idea is correct, it should be very hard (won't scratch with a steel knife blade), and very definitely will do no harm to the denizens of your tank!


You are correct that the nodule is intergrown or embedded in the limestone. I hope it is something benign like chert and not something metal or radioactive like uranium mined from the earth; my wife thinks Iím nuts. For this reason, Iím paranoid to try and scratch it with a knife.
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Coral




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PostPosted: Jul 24, 2019 11:09    Post subject: Re: What is embedded in this ancient reef rock?  

Peter Megaw wrote:
As Kevin notes, hard to tell from the images, but the thing does look porous, with "bubbles" that are more than half-spheres. This would rule out a meteorite since ablation surfaces tend to be scoop shaped instead of spherical

You could also test it with a magnet to see if it contains iron

Another possibility is a small piece of pumice...these can float long distances before becoming waterlogged...and there are plenty of volcanoes in the Caribbean that have pumped out pumice over the last 40 million years


I do see the porosity/bubbles you mention too. Iíll take pumice or chert, unfortunately for me, my mind always goes to worst case scenario, so I threw the rock out in the yard and havenít let my young kids help me with the tank water since I noticed this thing.
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Coral




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PostPosted: Jul 24, 2019 19:15    Post subject: Re: What is embedded in this ancient reef rock?  

I got some pictures of it dry today. I threw the rock out in my yard and didnít even realize there was a spider on it until I looked at the pictures, if it was something radioactive, I could have become Spider-Man! I didnít get bitten but I did manage to cut my finger somehow...


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Peter Lemkin




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PostPosted: Jul 25, 2019 02:09    Post subject: Re: What is embedded in this ancient reef rock?  

If it worries you, why not pry it out or carve it out. I doubt it contains heavy metals - they are rare as things go, but it would be easy to find out once it was out....as heavy metals are HEAVY and you could do a specific gravity and some other tests - but once it is out, it is out. Uranium is even rarer than most heavy elements and to me it sounds a bit paranoid to even imagine it might be. I agree with the others it is not a meteorite and I'm sure it is harmless, but since you fear it, I suggest you just cut it or pry it out.......
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vic rzonca




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PostPosted: Jul 25, 2019 07:43    Post subject: Re: What is embedded in this ancient reef rock?  

Would there be an alteration halo around the particle if it were radioactive? Likewise, would there be sign of oxidation if it where metallic?
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Coral




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PostPosted: Jul 25, 2019 12:43    Post subject: Re: What is embedded in this ancient reef rock?  

Peter Lemkin wrote:
If it worries you, why not pry it out or carve it out. I doubt it contains heavy metals - they are rare as things go, but it would be easy to find out once it was out....as heavy metals are HEAVY and you could do a specific gravity and some other tests - but once it is out, it is out. Uranium is even rarer than most heavy elements and to me it sounds a bit paranoid to even imagine it might be. I agree with the others it is not a meteorite and I'm sure it is harmless, but since you fear it, I suggest you just cut it or pry it out.......

You are right about about the paranoid part, that all started because I was googling what could be in limestone because any heavy metal would prevent me from collecting and successfully growing the types of corals I like; and thatís where I found an old paper online titled ďUranium in Carbonate RocksĒ which scared me.
I donít want to carve it out because that will cause me more paranoia about exposing myself, even though itís very unlikely to be radioactive. I already managed to break my skin on I believe the limestone part of the rock and that was just from trying to get a picture, let alone carve it out! To play it safe itís out of my aquarium now and Iíll probably throw it away. I really appreciate everyoneís feedback and still open to further comments.
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Peter Lemkin




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PostPosted: Jul 25, 2019 14:21    Post subject: Re: What is embedded in this ancient reef rock?  

Exposing yourself to what? Now you really do sound paranoid [sorry to say]. It is nothing harmful, almost surely not metal - and less so 'heavy metals', 99.9999999999% not Uranium - and many people have told you so, and told you how to easily remove it and find out. I suggest you throw it away - and stop dis-believing everyone here. We have tried to help, but your irrational, unscientific, and paranoid notions keep you paralyzed...... I handle very radioactive rocks full of Uranium and Radium sometimes - they are in my collection - and short exposure is not a problem - BUT YOUR DARK SPOT IS ONLY DANGEROUS IN YOUR MIND - not in fact! Another idea - surround your aquarium with lead bricks to keep out the maybe-radiation. Good luck.
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Coral




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PostPosted: Jul 25, 2019 14:40    Post subject: Re: What is embedded in this ancient reef rock?  

Peter Lemkin wrote:
Exposing yourself to what? Now you really do sound paranoid [sorry to say]. It is nothing harmful, almost surely not metal - and less so 'heavy metals', 99.9999999999% not Uranium - and many people have told you so, and told you how to easily remove it and find out. I suggest you throw it away - and stop dis-believing everyone here. We have tried to help, but your irrational, unscientific, and paranoid notions keep you paralyzed...... I handle very radioactive rocks full of Uranium and Radium sometimes - they are in my collection - and short exposure is not a problem - BUT YOUR DARK SPOT IS ONLY DANGEROUS IN YOUR MIND - not in fact! Another idea - surround your aquarium with lead bricks to keep out the maybe-radiation. Good luck.

I apologize for coming across as dis-believing what people say, that definitely was not my intention. I wholeheartedly appreciate what you have all said in this thread. In regards to the other things you said above, I agree with you.
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