Stone used as an abrasive (6)
I believe the answer is:
pumice
'stone used as an abrasive' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for pumice that I've seen before include "Lava stone" , "Solidified lava used as an abrasive" , "Mineral" , "Light porous stone used as polishing powder" , "Light form of solidified lava" .)