Soft mineral powder (4)
I believe the answer is:
talc
'soft mineral powder' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for talc that I've seen before include "Toilet powder - mica" , "Mineral used as a toiletry" , "After-bath powder" , "Powder used as toiletry" , "I may dust" .)