Theoretical Equilibrium Morphology of Gypsum (CaSO4•2H2O). 1. A Syncretic Strategy to Calculate the Morphology of Crystals

The theoretical and equilibrium morphology of gypsum (CaSO4 center dot 2H(2)O) is reassessed, starting from the historical papers by Simon and Bienfait (1965) and by Heijnen and Hartman (1991). The surface profiles of the most frequently observed crystal forms have been determined following two ways: in the first one we used the Hartman-Perdok method based on the periodic bond chain (PBC) analysis, while in the second one the profile of each face was obtained using the GDIS program. In both cases, the calculation of the specific surface energy values has been made using the general utility lattice program (GULP) code. From the synthesis of the two methods, a new and much more isotropic equilibrium shape is calculated, in the case of both unrelaxed and relaxed surfaces. Further, and for the first time, beyond the well-known and singular {010}, {120}, {0 (1) over bar1}, and {(1) over bar 11} F-forms, two stepped, {100} and {(1) over bar 22}, and one kinked form, {(1) over bar 02}, are found to build the equilibrium shape of gypsum.