Detritus

[darock73]

Is this detritus?

 

[Killerdrgn]

It's not, it's the dried grass type algae that you asked about a month ago.
Pedro identified it as turf algae.
http://www.manhattanreefs.com/forum/identification/48704-algae-question.html

 

[Marteen]

You may be able to blow it off the rock with a turkey baster... er reef blower.