Minerals found in forest (4)
I believe the answer is:
ores
'minerals' is the definition.
(ore is a kind of mineral)
'in forest' is the wordplay.
'in' indicates a hidden word.
'ORES' can be found hidden inside 'forest'.
'found' is the link.
(Other definitions for ores that I've seen before include "Rocks or minerals containing metals" , "Mined minerals" , "Sources of metal" , "Metal-bearing minerals" , "Mineral deposits" .)