For a while I have been working with gypsum I mined from a site in Utah, and I realized how low the temperature is to turn it into plaster, so I was wandering; has there ever been any cases of large deposits of gypsum being naturally heated into plaster and coming in contact with water?
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.