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Calcite crystals were nucleated and grown from supersaturated aqueous solutions in the presence of variable concentrations of lithium. The diagram of supersaturation vs [Li+]/[Ca2+] concentration ratio (“morphodrome”) shows a continuous habit variation, from the dominant {011̄1} rhombohedron (at low [Li+]/[Ca2+] ratio) to the dominant {0001} form (at high [Li+]/[Ca2+] ratio). The morphological change is interpreted in terms of two-dimensional layers having the structure of the monoclinic Li2CO3 crystal which are epitaxially adsorbed on the restructured {0001} form of calcite. Hence, even if {0001} is a K form (in the sense of Hartman-Perdok), the corresponding surface behaves like a F form, growing layer by layer from low to high supersaturation values.

The theoretical and equilibrium morphology of gypsum (CaSO4·2H2O) 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}, {01̅1}, and {1̅11} F-forms, two stepped, {100} and {1̅22}, and one kinked form, {1̅02}, are found to build the equilibrium shape of gypsum.

The structures of the (100), octopolar (111) Na-terminated [(111)Na], and (111) Cl-terminated [(111)Cl] surfaces of halite (NaCl) were determined by means of ab initio quantum mechanical calculations (density functional theory, DFT). The (111) surfaces show higher surface relaxation with respect to the (100) surface. The surface energies (γ) at T = 0 K for relaxed and unrelaxed (100) and (111) faces were determined at DFT level. The values of the surface energy for the relaxed faces are γ(100) = 160, γ(111)Cl = 390 and γ(111)Na = 405 erg/cm2; therefore, the stability order of relaxed surfaces reads: (100) < (111)Cl < (111)Na. For the unrelaxed faces, the surface energies are higher: γ(100) = 161, γ(111)Cl = 552 and γ(111)Na = 551 erg/cm2.To check if the octopolar (111) faces can belong to the equilibrium morphology of the crystal/vapor system, the relaxed surface energies at T > 0 K were calculated by considering both the vibrational motion of atoms and the surface configurational entropy. From these calculations it resulted that the octopolar (111)Na and (111)Cl faces cannot belong to the equilibrium morphology. Octopolar reconstruction and both surface vibrational and configurational entropy then allow us to explain why the {111} NaCl form cannot enter the equilibrium shape of the crystal.

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