Rock and Sand in the Reefers World, A geologists Perspective.

Excellent article, Neil :thumbup:

... the rock contains many different components….. dead SPS and LPS calcified branches, shells, sea sand and even other pieces of rock. These are held together by a matrix of calcium rich material, which is formed either through some sort of precipitation or through some sort of pressure, although it is my suspicion that the former is the real answer.
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As far as I know, much of what is sold as "live rock" is collected from the floor around existing reefs, and these are mostly broken-off parts of the actual reef - thus coral skeletons, with the remains of coralline algae "cementing" everything together.

Could you please elaborate on "Aragonite" - I know that it's quite rare, and sought-after by rock collectors in it's pure, crystalline form. The "aragonite" sold in the hobby is mined somewhere inland in the USA, from old marine deposits, I assume... Are these deposits in the form of large rocks, which are then blasted and crushed, or are they quarried from granular beds? Are there any such deposits in South Africa? Apart from the crystalline structure, are there any differences between aragonite and calcite?

Many more questions to follow:whistling:

Hennie
 
Hi All,

herewith replies to various comments.....

Maybe elaborate on the difference between shingle(sea-sand made up of shell fragments) and sea-sand(silica?).

These are unfortunately colloquial terms as opposed to a geological terms. In the sense of the question posed, from a geological perspective the major difference is both chemical and physical, chemical in that the “shingle” is mainly calcium while the silica is well silica…… physical because the shingle fragments would be small tabular bodies while the silica would be more round in nature. From a reefers perspective, I would go for the silica version, as stated above, the calcium would dissolve way too slowly to help the system of a marine tank, I would guess that the bacteria would be able to survive easier in the rounded silica, although it is a marginal call.

What about tufa (white/greyish) it's very porous. That will become LR once seeded with original LR?

Tufa is a sedimentary rock which is formed through chemical precipitation in inland water bodies many people refer to this as a type of travertine… while this is not strictly true, those who know what travertine is will recognize the layered nature of the rock…. Each layer representing a different depositional event. Tufa is a relatively porous rock composed predominantly of calcium (similar to limestone but not formed in a marine depositional environment) ….. From a reefers perspective, this rock would make excellent base rock which has great potential to become “live” but would not help with calcium levels. I am not aware of any significant deposits in south africa

It is important to note with every answer provided here that these are generalized answers and that a rock from one deposit with the same name as a rock from another deposit is likely to be vastly different despite their common names … if you want an example of this, do a google image search for granite pics !!

What about home made "Bio Rock" made with cement, arogonite, sand etc. To increase porosity some people mix salt with the cement mix and soak the dried rock in water afterwards so all the salt disolves.

I am not sure that this home made version of bio rock is worth all the fuss, I am currently investigating sources for natural rock and will keep MASAdonians posted on progress in this regard. The salt dissolving will increase the surface area of the rock and this would in turn increase the area available for bacteria populations. The Key here is porosity, how connected are these salt holes and I am afraid that in my educated opinion, the connectedness of the holes is dismal at best, a good porous sandstone or limestone would be 100x better as bio rock (which could develop into “live rock”) The major advantage of this home made version is that you can shape the rocks to your hearts content… and I have seen some stunning home made rock structures….. what I like is the idea of hiding the overflows etc with this sort of rock.


Another method is mixing plastic shavings with the cement. The theory is that cement will not bind to the plastic which makes the "rock" very pourous. In your opinion would these be of any benfit?

I have not personally read anything on this method so I will not venture too much of an opinion….. however is the shavings are not connected then the holes are not connected therefore the rock is not porous ……. Remember there are many ponds made from cement, the higher the ratio of cement to other components within the mixture the more waterproof the final product is ……as reefers making bio rock we tend to use very high ratio’s of cement for strength…. Thus we make waterproof and therefore non-porous bio rock.


Quote:
... the rock contains many different components….. dead SPS and LPS calcified branches, shells, sea sand and even other pieces of rock. These are held together by a matrix of calcium rich material, which is formed either through some sort of precipitation or through some sort of pressure, although it is my suspicion that the former is the real answer.

As far as I know, much of what is sold as "live rock" is collected from the floor around existing reefs, and these are mostly broken-off parts of the actual reef - thus coral skeletons, with the remains of coralline algae "cementing" everything together.

I would agree whole heartedly with this statement.

Could you please elaborate on "Aragonite" - I know that it's quite rare, and sought-after by rock collectors in it's pure, crystalline form. The "aragonite" sold in the hobby is mined somewhere inland in the USA, from old marine deposits, I assume... Are these deposits in the form of large rocks, which are then blasted and crushed, or are they quarried from granular beds? Are there any such deposits in South Africa? Apart from the crystalline structure, are there any differences between aragonite and calcite?



Don’t hold back there Hennie ;)…. You stirred up a can of worms with that question. :lol:!!

Aragonite, named after the town Aragon in Spain is an interesting rock, the type we look for our reefs is called oolitic aragonite. It is formed by concentric layers of calcium forming around microscopic impurities, dust sized particles….. Now two things can happen after formation of these ooids …. One they stay in the form of a sand, modern examples of this are seen in the Caribbean…. And that’s where most of our reefing aragonite comes from. Or they can solidify into a limestone….. famous deposits of this form of oolite aragonite occur in Indiana in the USA, and have been quarried for decades indeed they have been used in the construction of amongst other famous buildings, the pentagon. To answer your question…. In the carribean the aragonite could be simply bagged in Indiana it would have to be blasted and then crushed, which would result in rough / sharp edges.

Unfortunately there are no deposits of the oolitic aragonite sand beds in South Africa to my knowledge. I am also not aware of any significant differences between aragonite and calcite aside from the crystalline structure … although I am sure that on a detailed scientific level there are many …. The temperature at which the chemical structure is stable is definitely different, resulting in aragonite replacing calcite and vice versa in the fossil record…. A pain in the butt for paleontologists I believe.

Well that’s all for today gents, keep the questions coming, and i hope this thread is contributing to a better educated reefer ! :thumbup:
 
@Neil H Your interpretation is very interesting and informative however from it i get the impression that aragonite has no significant benefit over calcite. So being inquisitive me i have to ask why do the renowned aquarists, JS, RHF, BF, AC, JN etc all say use aragonite. Do not use Calcium carbonate. There must be some reason why.
 
The research that i have seen aids us in determining the difference between calcite and aragonite, but at this stage i am still searching for the real answer as to why aragonite is preferred

1) Aragonite is calcium carbonate (CaCO3) as is Calcite and they are polymorphs. Polymorphs means that they have the same chemical formula but different structures.
2) Aragonite has an Orthorhombic structure and calcite and Trigonal Structure....
3) The structure basically determines the hardness of the calcium carbonate or for its ability to increase the calcium content into the water chemistry at a reasonably high PH (as is calcium reacton PH NOT just a normal marine tank PH). So the structure somewhat determines the solubility.

So from what we have learned above it is correct to say that Aragonite is Calcium Carbonate and it is also correct to say that Calcite is Calcium Carbonate. However it is incorrect to say that calcium Carbonate is Aragonite and it is also incorrect to say that Calcium carbonate it Calcite. This is because they have different structures.

I give an analogy. Castle is beer. Amstel is beer. Beer is not Castle.

Further to the above, i think that the answer lies in the Oolitic structure..... the very rounded shape of the oolitic aragonite ...... remember not all aragonite is rounded oolitic particals...... is can completely solidify into a limestone (oolitic aragonite limestone) so not just any aragonite will do !! .......

i know oolitic calcite does occur and to be honest i dont know why oolitic aragonite is better than oolitic calcite ???? it is clear that the oolitic structure is best why the particular polymorph is better i just dont know..... perhaps the answer lies somewhere in the question why coke is better than pepsi ...... advertizing???????:whistling:

my search for the anwser to your question continues .......
 
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Time for the next installment in this thread.

Calcite VS Aragonite

Over the last few days I have done some in depth research into some of the differences between calcite and aragonite and have tried to summarize the differences that are important to us as reefers of which there are two:

Hardness (without going into too much detail, geologists measure a minerals hardness on a scale of 1 to 10, ten being the hardest and being equivalent to a diamonds hardness) Aragonite measures 3.5 to 4 on the hardness scale, while calcite measures only 3, this suggests that aragonite is more desirable because it is harder than calcite.

Specific Gravity (how heavy something is for a given volume) Aragonite is 2.95 while calcite is 2.6 to 2.8. this indicates that aragonite is more desirable because it is heavier (and less likely to result in a sand storm) than calcite.
 
NICE THREAD NEIL. THANKS!!!!!!!!! :thumbup: (back to my thread of my findings though...;))
 
Wow, putting that degree to excellent use here at MASA :thumbup:

My question, related to Ph, in a DSB, filled with aragonite, does the Ph levels drop/increase (which is the right one) significantly enough in the lower layers to allow the aragonite to dissolve and realease calcium?

or is it true that the aragonite releases a pH buffer(not so much the relase of calcium) into the water and hence aids with the prevention of pH roller coastering?
 
SchyffS said:
Wow, putting that degree to excellent use here at MASA :thumbup:

My question, related to Ph, in a DSB, filled with aragonite, does the Ph levels drop/increase (which is the right one) significantly enough in the lower layers to allow the aragonite to dissolve and realease calcium?

or is it true that the aragonite releases a pH buffer(not so much the relase of calcium) into the water and hence aids with the prevention of pH roller coastering?
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I would SUSPECT that yes the ph could drop to these levels, BUT i firmly believe that this release of calcium is wholeheartedly insufficient to surrport the calcium requirements of an SPS rich tank. the sze of the DSB would have to be huge and exceptional husbaandry applied.

Ph buffer question i will research and get back to you on !


sean_koekemoer said:
Wow, dunno how I missed this one too- deserves a gold rep. Thanks Neil
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thanks Sean, I enjoyed writing it
 
After thinking over the aragonite issue and having a great discussion with a fellow reefer, thanks boet, i think there is something extra that needs to be said about the use of aragonite in SUMPS.....

With the dropping of the PH in the DEEEP regions of the sand bed, small amounts of calcium (read aragonite) in a deep sand bed made of aragonite will begin to disolve, however as this small amount of calcium rises through the sand bed, clumping or redeposition of the calcium will take place due to the increasing ph environment.

So what does this mean? Well as the disolved particles rise up the ph rises and the particles come out of solution, as they are redeposited they may attach themselves to things like phosphates during the process of deposition (termed accretion by geologists) .... So there may be miniscule amounts of "nasties" removed out of the water column during this process.... but this phenominon again lends itself in support of Aragonite NOT suppling the corals calcium needs (it never gets into the DT) Also over time this clumping would in my opinion drastically reduce the effectiveness of the aragonite based DSB....

So for a DSB in my opinion aragonite is the wrong choice, a silica based material such as play sand or beach sand would hold up much better.
 
Hi NeilH,
Thanks for such an informative thread, I have often been ask by friends of mine why I cant use sand stone rocks in the marine tank. I am always told that they can get loads of these rocks from the sand dunes close to the beach. Please could you elaborate on these rocks.
Thanks
 
The old aragonite debate :whistling: it has been prooven and it is accepted that it does clump up and become less and less effective :thumbup: It is also accepted that it cannot supply the calcium needs of the DT etc ;) thats impossible.

Back to my question....the following was extracted from another source:
Aragonite and calcite are BOTH calcium carbonate (CaCO3). The only difference is in the shape of the crystalline structure. Check out your beach sand using the vinegar test to see if it fizzles and gives off carbon dioxide. If it contains calcium carbonate, it should react with the weak acetic acid (vinegar) and give off carbon dioxide. If you use muriatic acid (hydrochloric acid), you should be able to get the sand (assuming it is all calcareous sand) to completely dissolve if you add just a tablespoon or two to a half cup or more of acid.

P.S. -- The advantage of aragonite over calcite is that the crystalline structure of aragonite is less stable than calcite and therefore it breaks down at a higher pH than calcite. Both will break down if the pH is low enough.

So i understand from the above that it releases C02, the C02 is then released into the water and influences the pH.
Will this be a better use for aragonite: I would like to suggest that a second aragonite DSB(perhaps not as big as the silica based DSB) could be utilised to assist with pH buffering specifically. perhaps installed in a seperate bucket that can be maintained etc...will this be of any value to a system?

I dont really wanna get into a long debate about it, just a yes or no with a short reason why would suffice.
 
shane said:
Hi NeilH,
Thanks for such an informative thread, I have often been ask by friends of mine why I cant use sand stone rocks in the marine tank. I am always told that they can get loads of these rocks from the sand dunes close to the beach. Please could you elaborate on these rocks.
Thanks
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The short answer is yes you can use it, BUT it must be seeded properly and do not expect it to perform at the same level as live rock.... as an example 20kg of prous sandstond SHOULD do the same work as something like 10Kg of live rock.....and remember not all sandstone is suitable.... it needs lots of pores and spaces between the sane particles
 
SchyffS said:
The old aragonite debate :whistling: it has been prooven and it is accepted that it does clump up and become less and less effective :thumbup: It is also accepted that it cannot supply the calcium needs of the DT etc ;) thats impossible.

Back to my question....the following was extracted from another source:
Aragonite and calcite are BOTH calcium carbonate (CaCO3). The only difference is in the shape of the crystalline structure. Check out your beach sand using the vinegar test to see if it fizzles and gives off carbon dioxide. If it contains calcium carbonate, it should react with the weak acetic acid (vinegar) and give off carbon dioxide. If you use muriatic acid (hydrochloric acid), you should be able to get the sand (assuming it is all calcareous sand) to completely dissolve if you add just a tablespoon or two to a half cup or more of acid.

P.S. -- The advantage of aragonite over calcite is that the crystalline structure of aragonite is less stable than calcite and therefore it breaks down at a higher pH than calcite. Both will break down if the pH is low enough.

So i understand from the above that it releases C02, the C02 is then released into the water and influences the pH.
Will this be a better use for aragonite: I would like to suggest that a second aragonite DSB(perhaps not as big as the silica based DSB) could be utilised to assist with pH buffering specifically. perhaps installed in a seperate bucket that can be maintained etc...will this be of any value to a system?

I dont really wanna get into a long debate about it, just a yes or no with a short reason why would suffice.
Click to expand...

ok short answer in my opinion is No
reason.... the same CO2 that is released when the calcium is disolved into solution is used up when it comes out of solution.... So if we accept that the calcium does not make it all the way to the DT, and we accept clumping then we must also accept that the CO2 involved in this reaction would have the same sort of influence ... ie negligable

hope that was short enough ;)
 
Really great article backed by experience.
Aragonite is marketed better than reggies play sand :) but we can leave this for a beer discussion
Posted via Mobile Device
 
My 2c on the sandstone issue. Sandstone is made up of compressed sea sand/silica. In its forming process normally on land it collects PO4 and a whole lot of other substances. Most of these substances cause the Algae cyano blooms associated with sandstone. It was previously believed that the cause for these algae breakouts was the silicate in the sandstone.

Now here is a devil's advocate one. If sandstone is mainly silica and forms into rocks. Will sea sand/silica sand not do the same in a DSB? Now if you assume that sandstone is normally found above the water line and very little in the sea. It seams unlikely that clumping will occur.

So just as you have to collect live sand from clean deep areas of the sea to avoid contamination i would say dont use sandstone as you will have algae and cyano issues.
 
Ask anyone who saw my tank- half of my rock was sandstone and never had problems with them, even had Coraline overgrowing it as well as some funny "plants" growing out of them
 
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