Criticise rock (5)
I believe the answer is:
slate
This clue is a double definition.
'criticise' is the first definition.
(I've seen this before)
'rock' is the second definition.
(slate is a type of stone)
(Other definitions for slate that I've seen before include "Grey metamorphic rock" , "Blast" , "list of candidates" , "Roofing material or credit recorder" , "Roofing tile" .)