(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 one end of the
crystal, and is a dihexagonal pyramid. The hexagonal pyramids {hoh'l}
and (h.h.2'h'.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 (0001) and (0001').
Iodyrite (AgI), 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.