DITRIGONAL BIPYRAMIDAL CLASS Here there are three similar planes of symmetry intersecting in the triad axis, and perpendicular to them is a fourth plane of symmetry; at the intersection of the three vertical planes with the horizontal plane are three similar dyad axes ; there is no centre of symmetry.
The general form is bounded by twelve scalene triangles and is a ditrigonal bipyramid. Like the general form of the last class, this has two sets of indices { hkl, pqr} , for faces above the equatorial plane of symmetry and { pqr } for faces below : with hexagonal axes there would be only one set of indices. The hexagonal bipyramids, the hexagonal prism { I0I } and the basal pinacoid { 'III are geometrically the same in this class as in the holosymmetric class. The trigonal prism { 2 i i } and ditrigonal prisms { hid } are the same as in the ditrigonal pyramidal class.
The only representatives of this type of symmetry are the mineral benitoite (q.v.) and silver hydrogen phosphate, Ag2HPO4.