Aluminium ore (7)
I believe the answer is:
bauxite
'aluminium ore' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for bauxite that I've seen before include "Ore yielding aluminium" , "Ore which contains aluminium" , "Source of aluminium" , "Chief ore of aluminium" , "Clay-like compound" .)