Abrasive mineral (5)
'abrasive mineral' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for emery that I've seen before include "old comedian" , "Abrasive form of corundum" , "Rock used as abrasive" , "Hard, grey-black mineral used as 11 down" , "Abrasive powder" .)
(Other definitions for corundum that I've seen before include "Hard form of alumina" , "Stone" , "Extremely hard mineral used as an abrasive" , "Abrasive form of alumina" .)