Gypsum crystallizes not from amorphous precursors but through specific nanocrystalline forms that arise from subsaturated conditions, report researchers in Europe (Science, DOI: 10.1126/science.1215648). The findings contradict what scientists previously believed about nucleation behavior of gypsum, CaSO4•2H2O, which is used commercially in drywall and plaster and is also known for fouling pipes in desalination plants. The research team, led by Liane G. Benning, of England’s University of Leeds, and Juan Manuel García-Ruiz, of Spain’s University of Granada, studied nucleation and growth of CaSO4 and found that the material nucleates as nanocrystalline particles of bassanite, CaSO4•0.5H2O, that are 10–15 nm in diameter. Although the experimental solution concentrations were supersaturated for gypsum, they were not saturated for bassanite. The bassanite nanocrystals then evolve into porous nanorods up to 100 nm long. The nanorods aggregate and eventually transform into micrometer-sized gypsum crystals. Understanding bassanite formation prior to gypsum crystallization may help to reduce scaling in desalination plants, the authors say.