Oriented nucleation and growth of anhydrite during direct sulfation of limestone

The direct sulfation of limestone (Iceland Spar) was studied at 973 K in a fixed-bed reactor. Scanning electron microscopy examinations of the sulfated limestone particles show that the sulfation process involves oriented nucleation and growth of the solid product, anhydrite. The reason for the occurrence of oriented nucleation and growth of the solid product is related to a close two-dimensional lattice match between the lattice plane {1,0,4} of calcite and the lattice plane {(1) over bar ,1,0} of anhydrite.