Algae ID?

[DoomervilleG]

I suspect this is just part of the uglies as my tank is only 4 months + a couple days at this point, but I'm still curious. I've tried cleaning the rock with a stiff toothbrush, nothing came off, but my Astrea snails absolutely adore that rock. The Margarita and Nerites don't seem to give a darn about it.

 

[Zer0]

Probably the beginnings of coralline algae if it’s not coming off with a brush/scrubber.