Small retroditetrahedronary hexacosidishecatonicosachoron

The small retroditetrahedronary hexacosidishecatonicosachoron, or sirdtaxady, is a nonconvex uniform polychoron that consists of 600 regular tetrahedra, 120 regular dodecahedra, and 120 icosidodecahedra. 4 dodecahedra, 4 tetrahedra, and 6 icosidodecahedra join at each vertex.

If you expand a 120-cell by moving the cells away from the origin the right amount, without changing the orientation or size of the cells, and do the same to its dual 600-cell, and patch the icosidodecahedral holes in the result, you get a small retroditetrahedronary hexacosidishecatonicosachoron.

It is analogous to the small rhombicosidodecahedron, which is constructed by expanding a dodecahedron by moving the faces away from the origin the right amount, without changing the orientation or size of the faces, and do the same to its dual icosahedron, and patch the square holes in the result, you get a small rhombicosidodecahedron.

Vertex coordinates
Its vertices are the same as those of its regiment colonel, the small ditetrahedronary hexacosihecatonicosachoron.