The tailplane was also changed from dihedral to anhedral. The tailplane is straight edged with rounded tips and carries marked anhedral. Some biplanes have different degrees of dihedral/anhedral on different wings. Most aircraft have been designed with planar wings with simple dihedral (or anhedral). It crystallizes in the monoclinic system with prismatic, typically twinned forms, though usually anhedral. Perovskite occurs as small anhedral to subhedral crystals filling interstices between the rock-forming silicates. Aggregates can be formed of individual crystals with euhedral to anhedral grains. Chromite in podiform deposits form as anhedral grains. The production S-52-3 (HO5S-1) incorporated a downward sloping (anhedral) v-tail stabilizer. An aircraft with anhedral will show the opposite effect. Combined with strong anhedral, this layout produces stable flight in ground effect. These conflicting requirements led to the design of the 019's distinctive inverted-V, anhedral front profile. It also occurs in anhedral masses and tarnishes on exposure to air. Anhedral crystals do not, usually because the crystal is one grain in a polycrystalline solid.