Parry arcs are generated by double-oriented hexagonal column crystals, i.e. a so-called Parry orientation, where both the central main axis of the prism and the top and bottom prism side faces are oriented horizontally.
Parry arcs originate from double-oriented hexagonal column crystals with a specific orientation, known as Parry, in which the central axis of the prism and the horizontal faces of the prisms align.