Is this coral?

[KittenChiu]

Looks like it could be the mat of some kinda coral, but not sure. Rock came with the preowned tank and I had it under some other rocks when I set up the tank at my place, so dunno how much light it's gotten with me/if it ever looked different. But I just rearranged the tank and saw it. It looks smooth, but with "pores" here and there. Basically black under white light.

 

[Retro Reefer]

Looks like black sponge from the pictures.

 

[KittenChiu]

Thank you, never seen that before