In geometry, the truncated dodecahedron is an Archimedean solid. It has 12 regular decagonal faces, 20 regular triangular faces, 60 vertices and 90 edges.

Truncated dodecahedron
(Click here for rotating model)
Type	Archimedean solid Uniform polyhedron
Elements	F = 32, E = 90, V = 60 (χ = 2)
Faces by sides	20{3}+12{10}
Conway notation	tD
Schläfli symbols	t{5,3}
	t0,1{5,3}
Wythoff symbol	2 3 | 5
Coxeter diagram
Symmetry group	Ih, H3, [5,3], (*532), order 120
Rotation group	I, [5,3]+, (532), order 60
Dihedral angle	10-10: 116.57° 3-10: 142.62°
References	U26, C29, W10
Properties	Semiregular convex
Colored faces	3.10.10 (Vertex figure)
Triakis icosahedron (dual polyhedron)	Net

This polyhedron can be formed from a regular dodecahedron by truncating (cutting off) the corners so the pentagon faces become decagons and the corners become triangles.

It is used in the cell-transitive hyperbolic space-filling tessellation, the bitruncated icosahedral honeycomb.

The area A and the volume V of a truncated dodecahedron of edge length a are:

${\displaystyle {\begin{aligned}A&=5\left({\sqrt {3}}+6{\sqrt {5+2{\sqrt {5}}}}\right)a^{2}&&\approx 100.990\,76a^{2}\\V&={\tfrac {5}{12}}\left(99+47{\sqrt {5}}\right)a^{3}&&\approx 85.039\,6646a^{3}\end{aligned}}}$

Cartesian coordinates for the vertices of a truncated dodecahedron with edge length 2φ − 2, centered at the origin,^[1] are all even permutations of:

(0, ±1/φ, ±(2 + φ))

(±1/φ, ±φ, ±2φ)

(±φ, ±2, ±(φ + 1))

where φ = 1 + √5/2 is the golden ratio.

The truncated dodecahedron has five special orthogonal projections, centered: on a vertex, on two types of edges, and two types of faces. The last two correspond to the A₂ and H₂ Coxeter planes.

The truncated dodecahedron 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.

Schlegel diagrams are similar, with a perspective projection and straight edges.

It shares its vertex arrangement with three nonconvex uniform polyhedra:

It is part of a truncation process between a dodecahedron and icosahedron:

More information Family of uniform icosahedral polyhedra, Symmetry: [5,3], (*532) ...

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

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This polyhedron is topologically related as a part of sequence of uniform truncated polyhedra with vertex configurations (3.2n.2n), and [n,3] Coxeter group symmetry.

More information *n32 symmetry mutation of truncated spherical tilings: t{n,3}, Symmetry*n32 [n,3] ...

*n32 symmetry mutation of truncated spherical tilings: t{n,3}
Symmetry *n32 [n,3]	Spherical				Euclid.	Compact hyperb.		Paraco.
	*232 [2,3]	*332 [3,3]	*432 [4,3]	*532 [5,3]	*632 [6,3]	*732 [7,3]	*832 [8,3]...	*∞32 [∞,3]
Truncated figures
Symbol	t{2,3}	t{3,3}	t{4,3}	t{5,3}	t{6,3}	t{7,3}	t{8,3}	t{∞,3}
Triakis figures
Config.	V3.4.4	V3.6.6	V3.8.8	V3.10.10	V3.12.12	V3.14.14	V3.16.16	V3.∞.∞

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In the mathematical field of graph theory, a truncated dodecahedral graph is the graph of vertices and edges of the truncated dodecahedron, one of the Archimedean solids. It has 60 vertices and 90 edges, and is a cubic Archimedean graph.^[2]