If gypsum turns into plaster around 210 F, is there any natural plaster deposits or formations out there?
Water is removed from gypsum hydrate about 300 F+ making it dry powder gypsum. Water is added to gypsum to make "plaster of Paris" , no particular temperature is involved. Not sure it answers the question , but gypsum commonly deposits in oil production tubing. The produced oil/water/gas  mix cools as it comes up the well tubing and deposits in the tubing,; very difficult to prevent or remove.