Is this rock safe for my tank?

[Gene0514]

The dark color is from water

 

[Verbosity]

The dark color is from water

I'm a little doubtful of this

and this

Thanks!

What rock?

 

[Gene0514]

i posted the pics wrong, i just edited it

 

[haynchinook334]

yeah...scub it, and bake it, and then boil it....you'll be good.

 

[Gene0514]

ok thanks!

 

[Gene0514]

Well I managed to get most of the cement looking stuff off but the scissors slipped and sliced off some skin on my finger. They are supposed to be safety scissors lol. Here's the pic. I couldn't really take a better one.