# Snub dodecahedron

Snub dodecahedron

Type Archimedean solid
Uniform polyhedron
Elements F = 92, E = 150, V = 60 (χ = 2)
Faces by sides (20+60){3}+12{5}
Schläfli symbols sr{5,3}
ht0,1,2{5,3}
Wythoff symbol | 2 3 5
Coxeter diagram
Symmetry group I, ½H3, [5,3]+, (532), order 60
Rotation group I, [5,3]+, (532), order 60
Dihedral Angle 3-3:164°10'31" (164.18°)
3-5:152°55'53" (152.93°)
References U29, C32, W18
Properties Semiregular convex chiral

Colored faces

3.3.3.3.5
(Vertex figure)

Pentagonal hexecontahedron
(dual polyhedron)

Net

In geometry, the snub dodecahedron, or snub icosidodecahedron, is an Archimedean solid, one of thirteen convex isogonal nonprismatic solids constructed by two or more types of regular polygon faces.

The snub dodecahedron has 92 faces (the most of any convex uniform polyhedron other than prisms and antiprisms), of which 12 are pentagons and the other 80 are equilateral triangles. It also has 150 edges, and 60 vertices. It has two distinct forms, which are mirror images (or "enantiomorphs") of each other.

## Cartesian coordinates

Cartesian coordinates for the vertices of a snub dodecahedron are all the even permutations of

(±2α, ±2, ±2β),
(±(α+β/τ+τ), ±(−ατ+β+1/τ), ±(α/τ+βτ−1)),
(±(−α/τ+βτ+1), ±(−α+β/τ−τ), ±(ατ+β−1/τ)),
(±(−α/τ+βτ−1), ±(α−β/τ−τ), ±(ατ+β+1/τ)) and
(±(α+β/τ−τ), ±(ατ−β+1/τ), ±(α/τ+βτ+1)),

with an even number of plus signs, where

α = ξ − 1 / ξ

and

β = ξτ + τ2 + τ /ξ,

where τ = (1 + √5) / 2 is the golden ratio and ξ is the real solution to ξ3 − 2ξ = τ, which is the number:

$\xi = \sqrt[3]{\frac{\tau}{2} + \frac{1}{2}\sqrt{\tau - \frac{5}{27}}} + \sqrt[3]{\frac{\tau}{2} - \frac{1}{2}\sqrt{\tau - \frac{5}{27}}}$

or approximately 1.7155615.

This snub dodecahedron has an edge length of approximately 6.0437380841.

Taking the even permutations of the above coordinates with an odd number of plus signs gives another form, the enantiomorph of the other one.

## Surface area and volume

For a snub dodecahedron whose edge length is 1, the surface area is

$A = 20\sqrt{3} + 3\sqrt{25+10\sqrt{5}} \approx 55.28674495844515$

and the volume is

$V= \frac{12\xi^2(3\tau+1)-\xi(36\tau+7)-(53\tau+6)}{6\sqrt{3-\xi^2}^3} \approx 37.61664996273336$

where τ is the golden ratio.

The snub dodecahedron has the highest sphericity of all Archimedean solids.

## Orthogonal projections

The snub dodecahedron has two special orthogonal projections, centered, on two types of faces: triangles, and pentagons, correspond to the A2 and H2 Coxeter planes.

Orthogonal projections
Centered by Face
Triangle
Face
Pentagon
Edge
Image
Projective
symmetry
[3]+ [5]+ [2]

## Geometric relations

The snub dodecahedron can be generated by taking the twelve pentagonal faces of the dodecahedron and pulling them outward so they no longer touch. At a proper distance this can create the rhombicosidodecahedron by filling in square faces between the divided edges and triangle faces between the divided vertices. But for the snub form, only add the triangle faces and leave the square gaps empty. Then apply an equal rotation to the centers of the pentagons and triangles, continuing the rotation until the gaps can be filled by two equilateral triangles.

 Dodecahedron Rhombicosidodecahedron (Expanded dodecahedron) Snub dodecahedron

The snub dodecahedron can also be derived from the truncated icosidodecahedron by the process of alternation. Sixty of the vertices of the truncated icosidodecahedron form a polyhedron topologically equivalent to one snub dodecahedron; the remaining sixty form its mirror-image. The resulting polyhedron is vertex-transitive but not uniform, because its edges are of unequal lengths; some deformation is required to transform it into a uniform polyhedron.

Archimedes, an ancient Greek who showed major interest in polyhedral shapes, wrote a treatise on thirteen semi-regular solids. The snub dodecahedron is one of them.

## Related polyhedra and tilings

Family of uniform icosahedral polyhedra
Symmetry: [5,3], (*532) [5,3]+, (532)
{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
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

This semiregular polyhedron is a member of a sequence of snubbed polyhedra and tilings with vertex figure (3.3.3.3.n) and Coxeter–Dynkin diagram . These figures and their duals have (n32) rotational symmetry, being in the Euclidean plane for n=6, and hyperbolic plane for any higher n. The series can be considered to begin with n=2, with one set of faces degenerated into digons.

Dimensional family of snub polyhedra and tilings: 3.3.3.3.n
Symmetry
n32
[n,3]+
Spherical Euclidean Compact hyperbolic Paracompact
232
[2,3]+
D3
332
[3,3]+
T
432
[4,3]+
O
532
[5,3]+
I
632
[6,3]+
P6
732
[7,3]+
832
[8,3]+...
∞32
[∞,3]+
Snub
figure

3.3.3.3.2

3.3.3.3.3

3.3.3.3.4

3.3.3.3.5

3.3.3.3.6

3.3.3.3.7

3.3.3.3.8

3.3.3.3.∞
Coxeter
Schläfli

sr{2,3}

sr{3,3}

sr{4,3}

sr{5,3}

sr{6,3}

sr{7,3}

sr{8,3}

sr{∞,3}
Snub
dual
figure

V3.3.3.3.2

V3.3.3.3.3

V3.3.3.3.4

V3.3.3.3.5

V3.3.3.3.6

V3.3.3.3.7
V3.3.3.3.8 V3.3.3.3.∞
Coxeter