Crystal growth shape of whewellite polymorphs: Influence of structure distortions on crystal shape

The theoretical and experimental crystal growth shape has been determined for the two whewellite polymorphs. Theoretical studies consisted of PBC analysis, Donnay-Harker, Ising temperature, and Attachment Energy calculations. These calculations were based on accurate energy values, which were specially derived for the whewellite crystal structure by ab initio quantum mechanics. The morphology of crystals grown below and above the polymorph transition temperature is similar. However, theoretical morphologies are different, due to the doubling of the unit cell dimensions in the low-temperature structure. These results suggest a refinement of the thickness rule in Hartman-Perdock (H-P) theory. The Attachment Energy method is the most accurate of the three theoretical morphology methods used in this report. The high performance of the Ising model for this ionic crystal is probably due to the directionality of Ca-oxalate bonds. It has been found that crystal shape changes substantially along growth, massive penetration twinning occurs below the transition temperature, and the action of growth inhibitors is mainly directed to the (100) face. These phenomena are related to the crystal structure. The shape of whewellite natural crystals has been revised with the aim to show that the study of crystal shape can give clues about the growth conditions of natural crystals, with emphasis on renal calculi.