(Parallel-faced hemihedral).
Here there is a plane of symmetry perpendicular to the hexad axis;
there is also a centre of symmetry. All the closed forms are hexagonal
bipyramids; the open forms are hexagonal prisms or the basal pinacoid.
The general form {hikl} is hemihedral with parallel faces with respect
to the general form of the holosymmetric class.
Apatite (q.v.), pyromorphite, mimetite and vanadinite possess this
degree of symmetry.