Gypsum or calcium sulfate, is formed as a clear white rock or as a mineral where it appears as crystals. For most of us, we would recognise Gypsum as the rock or mineral we use to produce plaster, plaster board or cement for use in the construction industry. The rock is formed from the evaporation of sea water in the form of lagoons. This would have been a very gradual process, as the lagoons would have been replenished with sea water from time to time, but eventually gypsum in rock form would have formed.