Pentagonal antiprism

The pentagonal antiprism, or pap, is a prismatic uniform polyhedron. It consists of 10 triangles and 2 pentagons. Each vertex joins one pentagon and three triangles. As the name suggests, it is an antiprism based on a pentagon.

It can also be obtained as a diminishing of the regular icosahedron when two pentagonal pyramids are removed from opposite ends.

Vertex coordinates
A pentagonal antiprism of edge length 1 has vertex coordinates given by:
 * (±(1+$\sqrt{(5+√5)/8}$)/2, +1/2, 0),
 * (0, ±(1+$\sqrt{(5+√5)/10}$)/2, ±1/2),
 * (1/2, 0, (1+$\sqrt{5}$)/2),
 * (–1/2, 0, –(1+$\sqrt{5}$)/2).

These coordinates are obtained by removing two opposite vertices from a regular icosahedron.

An alternative set of coordinates can be constructed in a similar way to other polygonal antiprisms, giving the vertices as the following points along with their central inversions:


 * (±1/2, –$\sqrt{5}$, $\sqrt{(5–2√5)/15}$),
 * (±(1+$\sqrt{5}$)/4, $\sqrt{5}$, $\sqrt{5}$),
 * (0, $\sqrt{5}$, $\sqrt{(5+2√5)/20}$).

Representations
A pentagonal antiprism has the following Coxeter diagrams:


 * s2s10o (alternated decagonal prism)
 * s2s5s (alternated dipentagonal prism)
 * xo5ox&#x (bases considered separately)

Related polyhedra
A pentagonal pyramid can be attached to a base of the pentagonal antiprism to form the gyroelongated pentagonal pyramid. If a second pyramid is attached to the other base, the result is the gyroelongated pentagonal bipyramid, better known as the regular icosahedron.

Two non-prismatic uniform polyhedron compounds are composed of pentagonal antiprisms:


 * Great snub dodecahedron (6)
 * Great disnub dodecahedron (12)

There are also an infinite amount of prismatic uniform compounds that are the antiprisms of compounds of pentagons.