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