Mineral from the Black Forest (3)
I believe the answer is:
ore
'mineral' is the definition.
(I know that ore is a type of mineral)
'from the black forest' is the wordplay.
'from' indicates the answer is hidden within the clue.
'ORE' is hidden within 'black forest'.
(Other definitions for ore that I've seen before include "It's mined for minerals" , "coinage" , "Foreign currency" , "Raw material" , "store of value" .)