Geology buffs, anyone know what this is?

Has anyone seen a rock that looks like this before? More importantly, does anyone know if it will be safe in an aquarium? I lready did the vinegar test, and no fizzing so far.

 

@JJFury, My guess would be Ironstone; It has a reddish colour and the form is probably caused by erosion.

 

On the chance that i am correct, this would be safe to use in an aquarium as it would release iron into the water, this is generally not an issue (Planted Tanks) but you wont be able to manage the amount released. I know you can get ironstone gravel and according to specs you should not use more than 4kg per 50L; however these are gravel like pieces and would tent to release much faster as it has more exposed surface area. So depending on the rocks size and tank volume you might be able to give a good supply of Iron but this will take time to figure out.

This would have another side to it as we dont know how fast the rock releases its iron compared to the gravel; but im sure if you did a vinegar test and you saw no reddish foam or reddish liquid coming off im sure it will be a very slow release.

Use this info at your own risk

OH yes, you can test this with a Magnet. If it sticks its Iron stone.
Also a note that this stone can contain high amounts of Manganese, which again isn't bad for planted tanks - but again that varies on rate of release.

 

this may be a hard question to answer but does the rock feel heavier than a "normal" rock that size?

 

@ JJFury
Can you get a closer pic of the broken off areas?

 

Here is a close-up of a section where you can see some broken-off pieces as well as the insides of the 'cells'. It does not appear to be magnetic.

I finished hardscaping (I keep a few silver dollars) my tank today and added some fish. Since there are no plants, I suppose it will have to stay out of the tank.

Thanks for all the information any way, I've had this rock for a while now and always wondered what it is.

 

Depends on where you got it eg. Free state, Eastern Transvaal escarpment, Natal. All regions has got a different geology in the make-up of the top 100m crust.

 

Was not too sure but I am more convinced that this is a high grade ignimbrite made by a rheomorphic flow(Water pressurizing molten rock to the surface) and can be any type of material.
It can contain high traces of Iron(forget about a magnet test,My iron supplement is not magnetic!).

 

Thanks Slojo, this is all way above me, but I went in search (on Google) as well and came across the following link.

http://countryroads.typepad.com/cou...3/05/saturday-with-steve-honeycomb-rocks.html

The honeycomb rocks they describe here looks very similar to my rock. Is this not maybe what we are dealing with here?