What's this Black Stuff on my Live Rock?

Hey TRT,



I have these black spots showing up on my live rock (both in my 120 and in a little nano that my son has started up).



It's hard (not spongy) and appears to be black (or a very, very dark purple). You can see it's on both the cured fiji LA live rock and the purple coralline encrusted rock I got at the LFS.







Any idea what it could be? Coralline Algae?



Thanks,



Trent