Renoir forced to accept old mineral (4,3)
I believe the answer is:
iron ore
'mineral' is the definition.
(iron ore is a kind of mineral)
'renoir forced to accept old' is the wordplay.
'forced' is an anagram indicator.
'to accept' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'renoir' is an anagram of 'ironre'.
'ironre' enclosing 'o' is 'IRON-ORE'.
(Other definitions for iron ore that I've seen before include "Rock from which a metal can be extracted" , "From which a particular metal may be extracted" , "Material containing ferric metal" , "Aggregate from which the metal Fe can be extracted" , "source of heavy metal" .)