What is gypsum

What is gypsum?

Answer: Plaster of Paris reacts with water to give a hard mass called gypsum.
                   

(CaSO₄)₂. H₂O (s) + 3 H₂O (l)   →  2CaSO₄.2H₂O (s)
                      

Plaster for Paris      + Water     →  Gypsum