Formation of Orthorhombic Anhydrite

PHASE changes in solids are accompanied by the development of strain, voids, and other imperfections which disappear to some extent when the product stands at a temperature at which the rate of diffusion is appreciable. The processes taking place during these changes are not fully understood, and we have studied them in the transformation of soluble to orthorhombic anhydrite, that is, calcium sulphate of the same structure as the mineral anhydrite.