Merseburg
Merseburg : A process for making ammonium sulfate fertilizer from gypsum. The gypsum is slurried with water and ammonium carbonate solution added. Calcium carbonate precipitates and is removed, any excess of ammonium carbonate is neutralized with sulfuric acid, and the solution is concentrated until it crystallizes: CaSO4 +(NH4)2CO3 = CaCO3 + (NH4)2SO4. (Check source for accuracy of chemical formula)