Is this slate safe ?

I was about to clean my slate when I noticed this , Is this bad ?

 

Hard to tell from the picture, what is it?
Something on the surface or embedded in the rock?

 

It seems to be embedded , when scratched it does not flake. Here is another photo. I know they are not the best.

 

Looks like pyrite, an iron ore. It should not cause any issues.

 

Yeah, probably pyrite (also known as fool's gold). Not sure how safe it might be, but it's a very common thing in most bodies of water in my state (CA) and does not appear to cause problems.

 

I was researching different rocks for aquarium use the other day & ran across this link.



It does mention Iron Pyrite as something not to use in the aquarium.

 

While I would not use iron pyrite crystals ( I have a 4 pound one around here somewhere) that small amount, should not be an issue.

 

I was researching different rocks for aquarium use the other day & ran across this link.



It does mention Iron Pyrite as something not to use in the aquarium.

You mean it mentions it as something DEFINITELY not to use. O.O
Glad I read that...!

 

I've read that too.