Structural morphology of orthorhombic sulphur

Abstract

Using an interatomic potential function specific surface energies, attachment energies and slice energies have been calculated for 7 F faces and 18 S faces of orthorhombic sulphur. These energies are compared with statistical parameters (P values) for the frequency of occurrence of these faces on natural sulphur. It is found that P values are not correlated with the specific surface energies, except for the most important F faces. There is a positive correlation (r=0.881) with the surface energy per mol although this quantity has no physical meaning. It is supposed that an S face is due to alternating periods of dissolution (or evaporation) and growth, so that it occurs as a narrow face on the site of a previous edge. An excellent correlation (r=0.951) is found between the P value of an S face and a quantity P1P2ξh, where P1 and P2 are the P values of neighbouring faces that constitute the S face, ξ is proportional to the slice energy and h a distance determined by the interfacial angles of the three faces. This process should hold for the morphological development of any mineral, provided that no face-specific adsorption of cosolutes occurs.