Mineral in metal container (4)
I believe the answer is:
talc
'mineral' is the definition.
(talc is a kind of mineral)
'in metal container' is the wordplay.
'in' indicates a hidden word.
'TALC' is hidden within 'metal container'.
(Other definitions for talc that I've seen before include "Baby powder" , "In brief, popular body powder" , "White powder for the bathroom" , "Toilet powder - mica" , "Mica - scented body powder" .)