# Cuboctahedron

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In geometry, a **cuboctahedron** is a polyhedron with eight triangular faces and six square faces. A cuboctahedron has 12 identical vertices, with two triangles and two squares meeting at each, and 24 identical edges, each separating a triangle from a square. As such it is a quasiregular polyhedron, i.e. an Archimedean solid, being vertex-transitive and edge-transitive.

Its dual polyhedron is the rhombic dodecahedron.

## Contents

## Other names

*Heptaparallelohedron*(Buckminster Fuller)- Fuller applied the name "Dymaxion" to this shape, used in an early version of the Dymaxion map. He also called it the "Vector Equilibrium".
^{[1]}

- Fuller applied the name "Dymaxion" to this shape, used in an early version of the Dymaxion map. He also called it the "Vector Equilibrium".
- With O
_{h}symmetry, it is a*rectified cube*or*rectified octahedron*(Norman Johnson) - With T
_{d}symmetry, it is a*cantellated tetrahedron*. - With D
_{3d}symmetry, it is a*triangular gyrobicupola*.

## Area and volume

The area *A* and the volume *V* of the cuboctahedron of edge length *a* are:

## Orthogonal projections

The *cuboctahedron* has four special orthogonal projections, centered on a vertex, an edge, and the two types of faces, triangular and square. The last two correspond to the B_{2} and A_{2} Coxeter planes. The skew projections show a square and hexagon passing through the center of the cuboctahedron.

Square Face |
Triangular Face |
Vertex | Edge | Skew | |
---|---|---|---|---|---|

[4] | [6] | [2] | [2] | ||

Rhombic dodecahedron (Dual polyhedron) | |||||

## Spherical tiling

The cuboctahedron 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.

square-centered |
triangle-centered | |

orthographic projection | Stereographic projections |
---|

## Cartesian coordinates

The Cartesian coordinates for the vertices of a cuboctahedron (of edge length √2) centered at the origin are:

- (±1,±1,0)
- (±1,0,±1)
- (0,±1,±1)

An alternate set of coordinates can be made in 4-space, as 12 permutations of:

- (0,1,1,2)

This construction exists as one of 16 orthant facets of the cantellated 16-cell.

### Root vectors

The cuboctahedron's 12 vertices can represent the root vectors of the simple Lie group A_{3}. With the addition of 6 vertices of the octahedron, these vertices represent the 18 root vectors of the simple Lie group B_{3}.

## Dissection

The *cuboctahedron* can be dissected into two triangular cupola by a common hexagon passing through the center of the cuboctahedron. If these two triangular cupola are twisted so triangles and squares line up, Johnson solid J27, triangular orthobicupola is created.

The cuboctahedron can also be dissected into 6 square pyramids, and 8 tetrahedra meeting at a central point. This dissection is expressed in the alternated cubic honeycomb where pairs of square pyramids are combined into octahedra.

## Geometric relations

A cuboctahedron can be obtained by taking an appropriate cross section of a four-dimensional 16-cell.

A cuboctahedron has octahedral symmetry. Its first stellation is the compound of a cube and its dual octahedron, with the vertices of the cuboctahedron located at the midpoints of the edges of either.

The cuboctahedron is a rectified cube and also a rectified octahedron.

It is also a cantellated tetrahedron. With this construction it is given the Wythoff symbol: 3 3 | 2.

A skew cantellation of the tetrahedron produces a solid with faces parallel to those of the cuboctahedron, namely eight triangles of two sizes, and six rectangles. While its edges are unequal, this solid remains *vertex-uniform*: the solid has the full tetrahedral symmetry group and its vertices are equivalent under that group.

The edges of a cuboctahedron form four regular hexagons. If the cuboctahedron is cut in the plane of one of these hexagons, each half is a triangular cupola, one of the Johnson solids; the cuboctahedron itself thus can also be called a triangular gyrobicupola, the simplest of a series (other than the gyrobifastigium or "digonal gyrobicupola"). If the halves are put back together with a twist, so that triangles meet triangles and squares meet squares, the result is another Johnson solid, the triangular orthobicupola, also called an anticuboctahedron.

Both triangular bicupolae are important in sphere packing. The distance from the solid's center to its vertices is equal to its edge length. Each central sphere can have up to twelve neighbors, and in a face-centered cubic lattice these take the positions of a cuboctahedron's vertices. In a hexagonal close-packed lattice they correspond to the corners of the triangular orthobicupola. In both cases the central sphere takes the position of the solid's center.

Cuboctahedra appear as cells in three of the convex uniform honeycombs and in nine of the convex uniform 4-polytopes.

The volume of the cuboctahedron is 5/6 of that of the enclosing cube and 5/8 of that of the enclosing octahedron.

### Vertex arrangement

The cuboctahedron shares its edges and vertex arrangement with two nonconvex uniform polyhedra: the cubohemioctahedron (having the square faces in common) and the octahemioctahedron (having the triangular faces in common). It also serves as a cantellated tetrahedron, as being a rectified tetratetrahedron.

Cuboctahedron |
Cubohemioctahedron |
Octahemioctahedron |

The cuboctahedron 2-covers the tetrahemihexahedron,^{[2]} which accordingly has the same abstract vertex figure (two triangles and two squares: 3.4.3.4) and half the vertices, edges, and faces. (The actual vertex figure of the tetrahemihexahedron is 3.4.3/2.4, with the *a*/2 factor due to the cross.)

Cuboctahedron |
Tetrahemihexahedron |

## Related polyhedra

The cuboctahedron is one of a family of uniform polyhedra related to the cube and regular octahedron.

Template:Octahedral truncations

The cuboctahedron can be seen in a sequence of quasiregular polyhedrons and tilings: Template:Quasiregular figure table

This polyhedron is topologically related as a part of sequence of cantellated polyhedra with vertex figure (3.4.n.4), and continues as tilings of the hyperbolic plane. These vertex-transitive figures have (*n32) reflectional symmetry.

## Related polytopes

The cuboctahedron can be decomposed into a regular octahedron and eight irregular but equal octahedra in the shape of the convex hull of a cube with two opposite vertices removed. This decomposition of the cuboctahedron corresponds with the cell-first parallel projection of the 24-cell into three dimensions. Under this projection, the cuboctahedron forms the projection envelope, which can be decomposed into six square faces, a regular octahedron, and eight irregular octahedra. These elements correspond with the images of six of the octahedral cells in the 24-cell, the nearest and farthest cells from the 4D viewpoint, and the remaining eight pairs of cells, respectively.

## Cultural occurrences

- In the
*Star Trek*episode "By Any Other Name", aliens seize the Enterprise by transforming crew members into inanimate cuboctahedra. - The "Geo Twister" fidget toy [1] is a flexible cuboctahedron.
- The Coriolis space stations in the computer game
*Elite*are cuboctahedron-shaped.

## Cuboctahedral graph

Template:Infobox graph
In the mathematical field of graph theory, a **cuboctahedral graph** is the graph of vertices and edges of the cuboctahedron, one of the Archimedean solids. It has 12 vertices and 24 edges, and is a quartic graph Archimedean graph.^{[3]}

6-fold symmetry |

## See also

## References

- ↑ Vector Equilibrium: R. Buckminster Fuller
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- Template:The Geometrical Foundation of Natural Structure (book) (Section 3-9)
- Cromwell, P.
*Polyhedra*, CUP hbk (1997), pbk. (1999). Ch.2 p.79-86*Archimedean solids*