Form of gypsum (9)
I believe the answer is:
alabaster
'form of gypsum' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for alabaster that I've seen before include "Type of gypsum" , "statue material" , "Carved form of gypsum" , "White ornamental stone" , "Stab a real odd white mineral" .)