Theoretical Equilibrium Morphology of Gypsum (CaSO4·2H2O). 2. The Stepped Faces of the Main [001] Zone

• Published in: Crystal growth & design 2011-05, Vol.11 (5), p.1607-1614
• Main Authors: Massaro, Francesco Roberto, Rubbo, Marco, Aquilano, Dino
• Format: Article
• Language: English
• Subjects: Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Methods of crystal growth; physics of crystal growth; Physics; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg101570c

The athermal equilibrium shape (ES) of gypsum crystal is calculated, in a vacuum, in the zone interval of the stepped {1k0} forms (3 ≤ k ≤ 8). The surface profiles are obtained by applying either the Hartman−Perdok method of the periodic bond chains (PBC) or the method of systematic cuts (SC) generated under the only conditions of stoichiometry, electroneutrality, and annihilation of the dipole moment perpendicular to each d1k0 slice. The specific surface energy values γ1k0 have been calculated, both for ideal and relaxed surface profiles, using a semiempirical potential function proposed by Adam. From calculations, it follows that the ES in the [001] zone is characterized not only by the well-known {120} and {010} flat forms and by the stepped {100} pinacoid but also by the {140} and {180} stepped forms. Further, following the PBC method, the stepped {130} and {170} forms also should enter the ES. Finally, an unambiguous analogy arises between our results and the systematic presence of the {1k0} faces on the giant crystals found in the Naica mine, whose growth occurs very near the equilibrium.