06 April 2012
Vol 336, Issue 6077

About The Cover

Cover image expansion

COVER Polarized light micrograph of a thin section of gypsum crystals (CaSO4•2H2O). Vertical field of view ~4 millimeters. This natural and industrial mineral unexpectedly crystallizes from solution at room temperature upon a transition through a precursor, nanocrystalline bassanite (CaSO4•0.5H2O), a usually high-temperature phase. A detailed understanding of this crystallization route could lead to a new strategy to control gypsum scale and may open an alternative route for the production of "plaster of Paris" (bassanite). See page 69. Photo: Alfred Pasieka/Photo Researchers, Inc.