{1 0 0} and {1 1 1} forms of the NaCl crystals coexisting in growth from pure aqueous solution

Many papers dealing with the NaCl crystal morphology have been published since the 1960s. It is commonly recognized that solution-grown halite crystals usually show a richer morphology compared with those obtained from the vapour growth. Beside the cube, the {1 1 1} octahedron occurs both in the presence of surface-specific impurities and under well-defined supersaturations, in pure aqueous solution. In this paper, we confine our attention to the occurrence of the octahedron in growth from pure aqueous solution. Experimentally this was achieved cooling a saturated solution at 95 °C and following different temperature gradients. The octahedron stability in pure solution is discussed on the basis of the “octopole hypothesis” about the stability of the reconstructed NaCl (1 1 1) surface.