Not a critter, but what is this rock?

[miltonkl]

Picked up a batch of used rock from someone and most of it just looks like nothing special but some of it has this super spikey look to it. Just wondering if anyone knows if this is some kind of specific rock? I've only ever used marco style rock before and this all seems like some sort of former live rock maybe that I'm not familiar with. Just curious to learn about more about it since it's new to me! Maybe there isn't much to learn, I don't know!

Unique:

Versus the rest that seems more normal?

 

[fishguy242]

hi, Pukani in tub, rest misc dry ocean rock.