Pentagonal tegum

The pentagonal bipyramid, also called a pentagonal dipyramid, is a bipyramid with a pentagon as the equatorial section. Generally,a pentagonal bipyramid has 10 identical isosceles triangles as faces. It can be formed by joining two pentagonal pyramids at their bases.

Two specific cases of the general pentagonal bipyramid are notable. One such variation is obtained as the dual to the uniform pentagonal prism. The other is one of the Johnson solids, due to the pyramids having equilateral sides.

In vertex figures
The pentagonal bipyramid appears as the vertex figure of the nonuniform pentagonal duotegum. This vertex figure has an edge length of 1, and has no corealmic realization, because the Johnson pentagonal bipyramid has no circumscribed sphere.