Great snub icosidodecahedron

In geometry, the great snub icosidodecahedron is a nonconvex uniform polyhedron, indexed as U57.

It has 92 faces (80 triangles and 12 pentagrams), 150 edges, and 60 vertices.

[1] It can be represented by a Schläfli symbol sr{5⁄2,3}, and Coxeter-Dynkin diagram .

This polyhedron is the snub member of a family that includes the great icosahedron, the great stellated dodecahedron and the great icosidodecahedron.

In the book Polyhedron Models by Magnus Wenninger, the polyhedron is misnamed great inverted snub icosidodecahedron, and vice versa.

be the positive zero of the polynomial

is the golden ratio.

is the rotation around the axis

Let the linear transformations

be the transformations which send a point

with an even number of minus signs.

constitute the group of rotational symmetries of a regular tetrahedron.

constitute the group of rotational symmetries of a regular icosahedron.

are the vertices of a great snub icosahedron.

The edge length equals

, the circumradius equals

, and the midradius equals

For a great snub icosidodecahedron whose edge length is 1, the circumradius is Its midradius is The four positive real roots of the sextic in R2,

are, in order, the circumradii of the great retrosnub icosidodecahedron (U74), great snub icosidodecahedron (U57), great inverted snub icosidodecahedron (U69) and snub dodecahedron (U29).

The great pentagonal hexecontahedron (or great petaloid ditriacontahedron) is a nonconvex isohedral polyhedron and dual to the uniform great snub icosidodecahedron.

It has 60 intersecting irregular pentagonal faces, 120 edges, and 92 vertices.

Denote the golden ratio by

be the negative zero of the polynomial

Then each pentagonal face has four equal angles of

arccos ⁡ ( ξ ) ≈ 101.508

Each face has three long and two short edges.

between the lengths of the long and the short edges is given by The dihedral angle equals

Part of each face lies inside the solid, hence is invisible in solid models.

The other two zeroes of the polynomial

play a similar role in the description of the great inverted pentagonal hexecontahedron and the great pentagrammic hexecontahedron.