Soft rock (4)
I believe the answer is:
talc
'soft rock' 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 "It is used to absorb moisture" , "In brief, popular body powder" , "Cosmetic powder" , "Drier" , "Toilet powder - mica" .)