Stone identification and brittleness issue.

[Zak Rafik]

Hi all,
I got this large stone for my planted tank some time back. It weighs nearly 5 to 6 kilos.
Although it had lots character and colour, I was not so sure if it was an inert stone and if it won't affect water ph vales or any parameters.
The sales person from the LFS assured me it was inert but I doubt it

The area of the stone in the photos below which are marked in green tend to be brittle, especially around the edges.
Edges tend to break off quite easily with the least effort. The smaller stones do not have such problem.

Can any member identify this stone?

Cheers.

 

[Nelson]

Looks like a type of Shale.
Have you tried putting vinegar on it ?.
You could also try it in a bucket of water,for a while,and see if the PH changes.

 

[Zak Rafik]

Looks like a type of Shale.
Have you tried putting vinegar on it ?.
You could also try it in a bucket of water,for a while,and see if the PH changes.

Hi Nelson
Yes, I did try with vinegar and there were no fizzing.
As for ph test, it didn't cross my mind.

This is what I found about shale stone in Wiki
"Shales are typically composed of variable amounts of clay minerals and quartz grains and the typical color is gray."
"Shales and mudrocks contain roughly 95 percent of the organic matter in all sedimentary rocks."

 

[Nelson]

I'm no rock expert,so could be wrong .

 

[Berlioz]

I think shale too. It looks like the stuff I dig out of my backyard. I've used it before, but never long term, so I don't really know how well it holds up versus, say, seiryu or something like that. The bucket test is a good idea.

 

[sciencefiction]

I had this type of stone in a tank years back although on a lot smaller scale so maybe not large enough to have any impact. Fish were perfectly fine. The only thing I worried about is its sharp edges.

 

[Zak Rafik]

Even washing the stone with a plastic brush seems to break the edges.

 

[Berlioz]

Shale can be pretty brittle stuff. In fact, if you get a crack somewhere, you can usually pull the rock apart with your fingers.