Coarse rock some may remember on reflection (5)
I believe the answer is:
emery
'coarse rock' is the definition.
'some may remember on reflection' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'on reflection' says the letters should be written in reverse.
'yreme' can be found hidden inside 'may remember'.
'yreme' written backwards gives 'EMERY'.
(Other definitions for emery that I've seen before include "Dick - - , late comedian" , "Rock used as abrasive" , "old comedian" , "Hard grey-black mineral used as an abrasive" , "Black abrasive" .)