Bath powder mineral (4)
I believe the answer is:
talc
'bath powder 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 "Magnesium silicate powder" , "Bathroom dusting powder" , "Fragrant powder" , "Softest substance in Mohs scale of hardness" , "Cosmetic powder" .)