Mechanical selection of chiral crystals

A macroscopic chiral crystal (of size larger than one micron), slipping over an inclined solid support, should glide in a direction which differs slightly from the axis of maximum slope. This effect is linked to two factors: a) the crystal is firmly oriented, through the competition between weight forces and friction forces; b) there should exist a preferred direction of slip on the contact facet of the crystal. Similar effects are also expected with a crystal floating on a liquid surface, and driven horizontally by an external force (e.g., an air jet): here, the shape of the wet facet should control the preferred direction of slip.