Hexagonal bipyramid

A hexagonal bipyramid is a polyhedron formed from two hexagonal pyramids joined at their bases. The resulting solid has 12 triangular faces, 8 vertices and 18 edges. The 12 faces are identical isosceles triangles.

Hexagonal bipyramid
Typebipyramid
Faces12 triangles
Edges18
Vertices8
Schläfli symbol{ } + {6}
Coxeter diagram
Symmetry groupD6h, [6,2], (*226), order 24
Rotation groupD6, [6,2]+, (226), order 12
Dual polyhedronhexagonal prism
Face configurationV4.4.6
Propertiesconvex, face-transitive

Although it is face-transitive, it is not a Platonic solid because some vertices have four faces meeting and others have six faces, and because its faces are not equilateral triangles.

It is one of an infinite set of bipyramids. Having twelve faces, it is a type of dodecahedron, although that name is usually associated with the regular polyhedral form with pentagonal faces.

The hexagonal bipyramid has a plane of symmetry (which is horizontal in the figure to the right) where the bases of the two pyramids are joined. This plane is a regular hexagon. There are also six planes of symmetry crossing through the two apices. These planes are rhombic and lie at 30° angles to each other, perpendicular to the horizontal plane.

Images

It can be drawn as a tiling on a sphere which also represents the fundamental domains of [3,2], *322 dihedral symmetry:

The hexagonal bipyramid, dt{2,6}, can be in sequence truncated, tdt{2,6} and alternated (snubbed), sdt{2,6}:

The hexagonal bipyramid, dt{2,6}, can be in sequence rectified, rdt{2,6}, truncated, trdt{2,6} and alternated (snubbed), srdt{2,6}:

It the first polyhedra in a sequence defined by the face configuration V4.6.2n. This group is special for having all even number of edges per vertex and form bisecting planes through the polyhedra and infinite lines in the plane, and continuing into the hyperbolic plane for any

With an even number of faces at every vertex, these polyhedra and tilings can be shown by alternating two colors so all adjacent faces have different colors.

Each face on these domains also corresponds to the fundamental domain of a symmetry group with order 2,3,n mirrors at each triangle face vertex.

"Regular" right (symmetric) n-gonal bipyramids:
Name Digonal bipyramid Triangular bipyramid (J12) Square bipyramid (O) Pentagonal bipyramid (J13) Hexagonal bipyramid Heptagonal bipyramid Octagonal bipyramid Enneagonal bipyramid Decagonal bipyramid ... Apeirogonal bipyramid
Polyhedron image ...
Spherical tiling image Plane tiling image
Face configuration V2.4.4 V3.4.4 V4.4.4 V5.4.4 V6.4.4 V7.4.4 V8.4.4 V9.4.4 V10.4.4 ... V∞.4.4
Coxeter diagram ...

See also
  • Weisstein, Eric W. "Dipyramid". MathWorld.
  • Virtual Reality Polyhedra The Encyclopedia of Polyhedra
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