DIHEXAGONAL PYRAMIDAL  CLASS (

Hemimorphic-hemihedral) . Six planes of symmetry of two kinds intersect 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 oneend of the crystal, and is a dihexagonal pyramid . The hexagonal pyramids {hoTtl} and (h.h.2L.l) each consist of six faces at one end of the crystal . The prisms are geometrically the same as in the holosymmetric class . Perpendicular to the hexad axis are the pedions (000i) and (000I) . Iodyrite (Agl), greenockite (CdS), wurtzite (ZnS) and zincite (ZnO) are often placed in this class, but they more probably belong to the hemimorphic-hemihedral class of the rhombohedral division of this system .