Pentagonal dipyramid
| Pentagonal bipyramid | |
|---|---|
 |
|
| Type |
Bipyramid and Johnson J12 - J13 - J14 |
| Faces | 10 triangles |
| Edges | 15 |
| Vertices | 7 |
| Schläfli symbol | { } + {5} |
| Coxeter diagram |     |
| Symmetry group | D5h, [5,2], (*225), order 20 |
| Rotation group | D5, [5,2]+, (225), order 10 |
| Dual polyhedron | pentagonal prism |
| Face configuration | V4.4.5 |
| Properties | convex, face-transitive, (deltahedron) |
In geometry, the pentagonal bipyramid (or dipyramid) is third of the infinite set of face-transitive bipyramids. Each bipyramid is the dual of a uniform prism.
Although it is face-transitive, it is not a Platonic solid because some vertices have four faces meeting and others have five faces.
If the faces are equilateral triangles, it is a deltahedron and a Johnson solid (J13). It can be seen as two pentagonal pyramids (J2) connected by their bases.
A Johnson solid is one of 92 strictly convex polyhedra that have regular faces but are not uniform (that is, they are not Platonic solids, Archimedean solids, prisms or antiprisms). They were named by Norman Johnson, who first listed these polyhedra in 1966.
The pentagonal dipyramid is 4-connected, meaning that it takes the removal of four vertices to disconnect the remaining vertices. It is one of only four 4-connected simplicial well-covered polyhedra, meaning that all of the maximal independent sets of its vertices have the same size. The other three polyhedra with this property are the regular octahedron, the snub disphenoid, and an irregular polyhedron with 12 vertices and 20 triangular faces.
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