Powdery mineral (4)
I believe the answer is:
talc
'powdery mineral' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for talc that I've seen before include "After-bath powder" , "Soft white powder" , "Softest substance in Mohs scale of hardness" , "Baby powder" , "In brief, popular body powder" .)