Constituent of plaster of Paris (6)

I believe the answer is:

gypsum

(Other definitions for gypsum that I've seen before include "Plaster of Paris is made from this chalk-like mineral" , "Alabaster" , "Kind of chalk used to make plaster of Paris" , "Mineral used to make plaster of Paris" , "Mineral giving plaster of Paris" .)

I've seen this clue in The Times.

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