A macroscopic chiral crystal (of size larger than one micron), slipping ove
r an inclined solid support, should glide in a direction which differs slig
htly from the axis of maximum slope. This effect is linked to two factors:
a) the crystal is firmly oriented, through the competition between weight f
orces and friction forces; b) there should exist a preferred direction of s
lip 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.