What is this black stuff on my dry base rock?

[WheatToast]

I found this black stuff on a new piece of CaribSea South Sea Base Rock (it came out of the box a few days ago and has never entered my aquarium). It does not scrub off and appears to be encrusted on the rock. Should I worry about it?

 

[Oldreefer44]

IMO, No, nothing to worry about.

 

[WheatToast]

IMO, No, nothing to worry about.

Thanks! Any idea about what it is though.

 

[ying yang]

Some kind of mineral inside the rocks would be my guess.what mineral idk.
If any kind of metal then would a magnet stick to it?

 

[WheatToast]

bump