DIHEXAGONAL PYRAMIDAL CLASS (Hemimorphic-hemihedral.) Six planes of symmetry of two kinds in tersect in the hexad axis. The hexad axis is uniterminal and all the forms are open forms. The general form { hikl } consists of twelve faces at one end of the crystal, and is a dihexagonal pyramid. The hexagonal pyramids { hohl } and { h.h. ali.l } each con sist of six faces at one end of the crystal. The prisms are geometrically the same as in the holo-symmetric class. Perpendicular to the hexad axis are the pedions { 0001 } and { o°o is } .
Iodyrite (AgI), greenockite (CdS), wurtzite (Zns) and zincite (ZnO) are often placed in this class, but they more prob ably belong to the hemimorphic-hemihedral class of the rhombohedral division of this system.