Fur, black, found in market (5)
I believe the answer is:
sable
'fur' is the definition.
(sable is a kind of fur)
'black found in market' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'found in' is an insertion indicator.
'market' becomes 'sale' (I've seen this in other clues).
'b' going within 'sale' is 'SABLE'.
(Other definitions for sable that I've seen before include "Dark brown fur of the marten" , "fur coat" , "Antelope, fur" , "(Fur from) small carnivore" , "Marten's fur - dark black" .)