Very soft mineral (4)
I believe the answer is:
talc
'very soft mineral' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for talc that I've seen before include "Baby powder" , "Toilet powder - mica" , "It is used to absorb moisture" , "Softest mineral on Mohs hardness scale" , "Cosmetic powder" .)