The Rhombicosidodecahedron
The rhombicosidodecahedron, also known as the small rhombicosidodecahedron, is a 3D uniform polyhedron bounded by 20 triangles, 30 squares, and 12 pentagons. It may be constructed by radially expanding the pentagonal faces of the dodecahedron outwards, or equivalently, the triangular faces of the icosahedron outwards.
The 12 pentagonal faces correspond with the faces of the dodecahedron, the 20 triangular faces correspond with the faces of the icosahedron, and the 30 square faces correspond with the edges of both the dodecahedron and the icosahedron.
Projections
In order to be able to identify the rhombicosidodecahedron in various projections of 4D objects, it is useful to know how it appears from various viewpoints. The following are some of the commonlyencountered views:
Projection  Envelope  Description 

Decagon  Parallel projection centered on a pentagonal face. The edges of the projection are the images of 10 of the square faces. 

Dodecagon  Parallel projection centered on a triangular face. 

Dodecagon  Parallel projection centered on a square face. 

Tetradecagon  Vertexcentered parallel projection. 
Coordinates
The Cartesian coordinates of the rhombicosidodecahedron, centered on the origin and having edge length 2, are all permutations of coordinates and changes of sign of:
 (1, 1, φ^{3})
together with all even permutations of coordinates and changes of sign of:
 (0, φ^{2}, φ√5)
 (φ, 2φ, φ^{2})
where φ=(1+√5)/2 is the Golden Ratio.
Occurrences
The rhombicosidodecahedron occurs as cells in the following uniform polychora:
 The cantellated 120cell;
 The runcitruncated 600cell.
It also occurs in the following CRF polychora: