Icosidodecahedron

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Icosidodecahedron
Icosidodecahedron
(Click here for rotating model)
Type Archimedean solid
Uniform polyhedron
Elements F = 32, E = 60, V = 30 (χ = 2)
Faces by sides 20{3}+12{5}
Conway notation aD
Schläfli symbols r{5,3}
t1{5,3}
Wythoff symbol 2 | 3 5
Coxeter diagram CDel node.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node.png
Symmetry group Ih, H3, [5,3], (*532), order 120
Rotation group I, [5,3]+, (532), order 60
Dihedral Angle 142.62°
 \cos^{-1} \left(-\sqrt{\frac{1}{15}\left(5+2\sqrt{5}\right)}\right)
References U24, C28, W12
Properties Semiregular convex quasiregular
Icosidodecahedron.png
Colored faces
Icosidodecahedron
3.5.3.5
(Vertex figure)
Rhombictriacontahedron.svg
Rhombic triacontahedron
(dual polyhedron)
Icosidodecahedron flat.svg
Net
A Hoberman sphere as an icosidodecahedron

In geometry, an icosidodecahedron is a polyhedron with twenty triangular faces and twelve pentagonal faces. An icosidodecahedron has 30 identical vertices, with two triangles and two pentagons meeting at each, and 60 identical edges, each separating a triangle from a pentagon. As such it is one of the Archimedean solids and more particularly, a quasiregular polyhedron.

An icosidodecahedron has icosahedral symmetry, and its first stellation is the compound of a dodecahedron and its dual icosahedron, with the vertices of the icosahedron located at the midpoints of the edges of either.

Its dual polyhedron is the rhombic triacontahedron. An icosidodecahedron can be split along any of six planes to form a pair of pentagonal rotundae, which belong among the Johnson solids.

The icosidodecahedron can be considered a pentagonal gyrobirotunda, as a combination of two rotundae (compare pentagonal orthobirotunda, one of the Johnson solids). In this form its symmetry is D5d, [10,2+], (2*5), order 20.

The wire-frame figure of the icosidodecahedron consists of six flat regular decagons, meeting in pairs at each of the 30 vertices.

Cartesian coordinates[edit]

Convenient Cartesian coordinates for the vertices of an icosidodecahedron with unit edges are given by:[1]

  • (0,0,±φ)
  • (0,±φ,0)
  • (±φ,0,0)
  • (±1/2, ±φ/2, ±(1+φ)/2)
  • (±φ/2, ±(1+φ)/2, ±1/2)
  • (±(1+φ)/2, ±1/2, ±φ/2)

where φ is the golden ratio, (1+√5)/2.

Orthogonal projections[edit]

The icosidodecahedron has four special orthogonal projections, centered on a vertex, an edge, a triangular face, and a pentagonal face. The last two correspond to the A2 and H2 Coxeter planes.

Orthogonal projections
Centered by Vertex Edge Face
Triangle
Face
Pentagon
Image Dodecahedron t1 v.png Dodecahedron t1 e.png Dodecahedron t1 A2.png Dodecahedron t1 H3.png
Projective
symmetry
[2] [2] [6] [10]
Dual
image
Dual dodecahedron t1 v.png Dual dodecahedron t1 e.png Dual dodecahedron t1 A2.png Dual dodecahedron t1 H3.png

Surface area and volume[edit]

The surface area A and the volume V of the icosidodecahedron of edge length a are:

A = \left(5\sqrt{3}+3\sqrt{25+10\sqrt{5}}\right) a^2 \approx 29.3059828a^2
V = \frac{1}{6} \left(45+17\sqrt{5}\right) a^3 \approx 13.8355259a^3.

Spherical tiling[edit]

The icosidodecahedron can also be represented as a spherical tiling, and projected onto the plane via a stereographic projection. This projection is conformal, preserving angles but not areas or lengths. Straight lines on the sphere are projected as circular arcs on the plane.

Uniform tiling 532-t1.png Icosidodecahedron stereographic projection pentagon.png
Pentagon-centered
Icosidodecahedron stereographic projection triangle.png
Triangle-centered
Orthographic projection Stereographic projections

Related polyhedra[edit]

The icosidodecahedron is a rectified dodecahedron and also a rectified icosahedron, existing as the full-edge truncation between these regular solids.

The icosidodecahedron contains 12 pentagons of the dodecahedron and 20 triangles of the icosahedron:

Family of uniform icosahedral polyhedra
Symmetry: [5,3], (*532) [5,3]+, (532)
CDel node 1.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node.png CDel node 1.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node.png CDel node.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node.png CDel node.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node 1.png CDel node.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node 1.png CDel node 1.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node 1.png CDel node 1.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node 1.png CDel node h.pngCDel 5.pngCDel node h.pngCDel 3.pngCDel node h.png
Uniform polyhedron-53-t0.png Uniform polyhedron-53-t01.png Uniform polyhedron-53-t1.png Uniform polyhedron-53-t12.png Uniform polyhedron-53-t2.png Uniform polyhedron-53-t02.png Uniform polyhedron-53-t012.png Uniform polyhedron-53-s012.png
{5,3} t{5,3} r{5,3} 2t{5,3}=t{3,5} 2r{5,3}={3,5} rr{5,3} tr{5,3} sr{5,3}
Duals to uniform polyhedra
CDel node f1.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node.png CDel node f1.pngCDel 5.pngCDel node f1.pngCDel 3.pngCDel node.png CDel node.pngCDel 5.pngCDel node f1.pngCDel 3.pngCDel node.png CDel node.pngCDel 5.pngCDel node f1.pngCDel 3.pngCDel node f1.png CDel node.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node f1.png CDel node f1.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node f1.png CDel node f1.pngCDel 5.pngCDel node f1.pngCDel 3.pngCDel node f1.png CDel node fh.pngCDel 5.pngCDel node fh.pngCDel 3.pngCDel node fh.png
Icosahedron.svg Triakisicosahedron.jpg Rhombictriacontahedron.svg Pentakisdodecahedron.jpg POV-Ray-Dodecahedron.svg Deltoidalhexecontahedron.jpg Disdyakistriacontahedron.jpg Pentagonalhexecontahedronccw.jpg
V5.5.5 V3.10.10 V3.5.3.5 V5.6.6 V3.3.3.3.3 V3.4.5.4 V4.6.10 V3.3.3.3.5

The icosidodecahedron can be seen in a sequence of quasiregular polyhedrons and tilings:

Dimensional family of quasiregular polyhedra and tilings: 3.n.3.n
Symmetry
*n32
[n,3]
Spherical Euclidean Compact hyperbolic Paracompact Noncompact
*332
[3,3]
Td
*432
[4,3]
Oh
*532
[5,3]
Ih
*632
[6,3]
p6m
*732
[7,3]
*832
[8,3]...
*∞32
[∞,3]
 
[iπ/λ,3]
Quasiregular
figures
configuration
Uniform tiling 332-t1-1-.png
3.3.3.3
Uniform tiling 432-t1.png
3.4.3.4
Uniform tiling 532-t1.png
3.5.3.5
Uniform tiling 63-t1.png
3.6.3.6
Uniform tiling 73-t1.png
3.7.3.7
Uniform tiling 83-t1.png
3.8.3.8
H2 tiling 23i-2.png
3.∞.3.∞
3.∞.3.∞
Coxeter diagram CDel node.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node.png CDel node.pngCDel 4.pngCDel node 1.pngCDel 3.pngCDel node.png CDel node.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node.png CDel node.pngCDel 6.pngCDel node 1.pngCDel 3.pngCDel node.png CDel node.pngCDel 7.pngCDel node 1.pngCDel 3.pngCDel node.png CDel node.pngCDel 8.pngCDel node 1.pngCDel 3.pngCDel node.png CDel node.pngCDel infin.pngCDel node 1.pngCDel 3.pngCDel node.png CDel node.pngCDel ultra.pngCDel node 1.pngCDel 3.pngCDel node.png
Dual
(rhombic)
figures
configuration
Hexahedron.svg
V3.3.3.3
Rhombicdodecahedron.jpg
V3.4.3.4
Rhombictriacontahedron.svg
V3.5.3.5
Rhombic star tiling.png
V3.6.3.6
Order73 qreg rhombic til.png
V3.7.3.7
Uniform dual tiling 433-t01-yellow.png
V3.8.3.8
Ord3infin qreg rhombic til.png
V3.∞.3.∞
Coxeter diagram CDel node.pngCDel 3.pngCDel node f1.pngCDel 3.pngCDel node.png CDel node.pngCDel 4.pngCDel node f1.pngCDel 3.pngCDel node.png CDel node.pngCDel 5.pngCDel node f1.pngCDel 3.pngCDel node.png CDel node.pngCDel 6.pngCDel node f1.pngCDel 3.pngCDel node.png CDel node.pngCDel 7.pngCDel node f1.pngCDel 3.pngCDel node.png CDel node.pngCDel 8.pngCDel node f1.pngCDel 3.pngCDel node.png CDel node.pngCDel infin.pngCDel node f1.pngCDel 3.pngCDel node.png CDel node.pngCDel ultra.pngCDel node f1.pngCDel 3.pngCDel node.png
Dimensional family of quasiregular polyhedra and tilings: 5.n.5.n
Symmetry
*5n2
[n,5]
Spherical Hyperbolic... Paracompact Noncompact
*352
[3,5]
*452
[4,5]
*552
[5,5]
*652
[6,5]
*752
[7,5]
*852
[8,5]...
*∞52
[∞,5]
 
[iπ/λ,5]
Coxeter CDel node.pngCDel 3.pngCDel node 1.pngCDel 5.pngCDel node.png CDel node.pngCDel 4.pngCDel node 1.pngCDel 5.pngCDel node.png CDel node.pngCDel 5.pngCDel node 1.pngCDel 5.pngCDel node.png CDel node.pngCDel 6.pngCDel node 1.pngCDel 5.pngCDel node.png CDel node.pngCDel 7.pngCDel node 1.pngCDel 5.pngCDel node.png CDel node.pngCDel 8.pngCDel node 1.pngCDel 5.pngCDel node.png CDel node.pngCDel infin.pngCDel node 1.pngCDel 5.pngCDel node.png CDel node.pngCDel ultra.pngCDel node 1.pngCDel 5.pngCDel node.png
Quasiregular
figures
configuration
Uniform tiling 532-t1.png
5.3.5.3
Uniform tiling 54-t1.png
5.4.5.4
H2 tiling 255-2.png
5.5.5.5
H2 tiling 256-2.png
5.6.5.6
H2 tiling 257-2.png
5.7.5.7
H2 tiling 258-2.png
5.8.5.8
H2 tiling 25i-2.png
5.∞.5.∞
 
5.∞.5.∞
Dual figures
Coxeter CDel node.pngCDel 3.pngCDel node f1.pngCDel 5.pngCDel node.png CDel node.pngCDel 4.pngCDel node f1.pngCDel 5.pngCDel node.png CDel node.pngCDel 5.pngCDel node f1.pngCDel 5.pngCDel node.png CDel node.pngCDel 6.pngCDel node f1.pngCDel 5.pngCDel node.png CDel node.pngCDel 7.pngCDel node f1.pngCDel 5.pngCDel node.png CDel node.pngCDel 8.pngCDel node f1.pngCDel 5.pngCDel node.png CDel node.pngCDel infin.pngCDel node f1.pngCDel 5.pngCDel node.png CDel node.pngCDel ultra.pngCDel node f1.pngCDel 5.pngCDel node.png
Dual
(rhombic)
figures
configuration
Rhombictriacontahedron.jpg
V5.3.5.3
Order-5-4 quasiregular rhombic tiling.png
V5.4.5.4
H2 tiling 245-4.png
V5.5.5.5
Order-6-5 quasiregular rhombic tiling.png
V5.6.5.6

V5.7.5.7

V5.8.5.8

V5.∞.5.∞
V5.∞.5.∞

Pentagonal gyrobirotunda[edit]

It is also related to the Johnson solid called a pentagonal orthobirotunda created by two pentagonal rotunda connected as mirror images.

Dissected icosidodecahedron.png
(Dissection)
Icosidodecahedron.png
Icosidodecahedron
(pentagonal gyrobirotunda)
Pentagonal orthobirotunda solid.png
Pentagonal orthobirotunda
Pentagonal rotunda.png
Pentagonal rotunda

Eight uniform star polyhedra share the same vertex arrangement. Of these, two also share the same edge arrangement: the small icosihemidodecahedron (having the triangular faces in common), and the small dodecahemidodecahedron (having the pentagonal faces in common). The vertex arrangement is also shared with the compounds of five octahedra and of five tetrahemihexahedra.

Icosidodecahedron.png
Icosidodecahedron
Small icosihemidodecahedron.png
Small icosihemidodecahedron
Small dodecahemidodecahedron.png
Small dodecahemidodecahedron
Great icosidodecahedron.png
Great icosidodecahedron
Great dodecahemidodecahedron.png
Great dodecahemidodecahedron
Great icosihemidodecahedron.png
Great icosihemidodecahedron
Dodecadodecahedron.png
Dodecadodecahedron
Small dodecahemicosahedron.png
Small dodecahemicosahedron
Great dodecahemicosahedron.png
Great dodecahemicosahedron
Compound of five octahedra.png
Compound of five octahedra
UC18-5 tetrahemihexahedron.png
Compound of five tetrahemihexahedra

Related polytopes[edit]

In four-dimensional geometry the icosidodecahedron appears in the regular 600-cell as the equatorial slice that belongs to the vertex-first passage of the 600-cell through 3D space. In other words: the 30 vertices of the 600-cell which lie at arc distances of 90 degrees on its circumscribed hypersphere from a pair of opposite vertices, are the vertices of an icosidodecahedron. The wire frame figure of the 600-cell consists of 72 flat regular decagons. Six of these are the equatorial decagons to a pair of opposite vertices. They are precisely the six decagons which form the wire frame figure of the icosidodecahedron.

See also[edit]

Notes[edit]

References[edit]

  • Williams, Robert (1979). The Geometrical Foundation of Natural Structure: A Source Book of Design. Dover Publications, Inc. ISBN 0-486-23729-X.  (Section 3-9)
  • Cromwell, P. (1997). Polyhedra. United Kingdom: Cambridge. pp. 79–86 Archimedean solids. ISBN 0-521-55432-2. 

External links[edit]