Rhombicuboctahedron

The rhombicuboctahedron, or small rhombicuboctahedron, is an Archimedean solid with eight triangular and eighteen square faces. There are 24 identical vertices, with one triangle and three squares meeting at each. Note that six of the squares only share vertices with the triangles while the other twelve share an edge. The polyhedron has octahedral symmetry, like the cube and octahedron. Its dual is called the deltoidal icositetrahedron or trapezoidal icositetrahedron, although its faces are not really true trapezoids.

The name "rhombicuboctahedron" refers to the fact that 12 of the square faces lie in the same planes as the 12 faces of the rhombic dodecahedron which is dual to the cuboctahedron. "Great rhombicuboctahedron" is an alternative name for a truncated cuboctahedron, whose faces are parallel to those of the (small) rhombicuboctahedron.

It can also called a "cantellated cube" or a "cantellated octahedron" from truncation operations of the uniform polyhedron.

Area and volume

The area "A" and the volume "V" of the rhombicuboctahedron of edge length "a" are::$A\; =\; (18+2sqrt\{3\})a^2\; approx\; 21.4641016a^2$:$V\; =\; frac\{1\}\{3\}\; (12+10sqrt\{2\})a^3\; approx\; 8.71404521a^3.$

Cartesian coordinates

Cartesian coordinates for the vertices of a rhombicuboctahedron centred at the origin, with edge length 2 units, are all permutations of : (±1, ±1, ±(1+√2)).

Geometric relations

There are three pairs of parallel planes that each intersect the rhombicuboctahedron through eight edges in the form of a regular octagon. The rhombicuboctahedron may be divided along any of these to obtain an octagonal prism with regular faces and two additional polyhedra called square cupolae, which count among the Johnson solids. These can be reassembled to give a new solid called the "pseudorhombicuboctahedron" (or elongated square gyrobicupola) with the symmetry of a square antiprism. In this the vertices are all locally the same as those of a rhombicuboctahedron, with one triangle and three squares meeting at each, but are not all identical with respect to the entire polyhedron, since some are closer to the symmetry axis than others.

There are distortions of the rhombicuboctahedron that, while some of the faces are not regular polygons, are still vertex-uniform. Some of these can be made by taking a cube or octahedron and cutting off the edges, then trimming the corners, so the resulting polyhedron has six square and twelve rectangular faces. These have octahedral symmetry and form a continuous series between the cube and the octahedron, analogous to the distortions of the rhombicosidodecahedron or the tetrahedral distortions of the cuboctahedron. However, the rhombicuboctahedron also has a second set of distortions with six rectangular and sixteen trapezoidal faces, which do not have octahedral symmetry but rather T_h symmetry, so they are invariant under the same rotations as the tetrahedron but different reflections.

The lines along which a Rubik's Cube can be turned are, projected onto a sphere, similar, topologically identical, to a rhombicuboctahedron's edges. In fact, variants using the Rubik's Cube mechanism have been produced which closely resemble the rhombicuboctahedron.

The rhombicuboctahedron is used in three uniform space-filling tessellations: the cantellated cubic honeycomb, the runcitruncated cubic honeycomb, and the runcinated alternated cubic honeycomb.

It shares its vertex arrangement with three uniform star polyhedrons: the stellated truncated hexahedron, the small rhombihexahedron, and the small cubicuboctahedron.

In the arts

The polyhedron in the portrait of Luca Pacioli is a glass rhombicuboctahedron half-filled with water.

ee also

*cube
*Cuboctahedron
*Octahedron
*Rhombicosidodecahedron
*Compound of five small rhombicuboctahedra
*Truncated cuboctahedron (great rhombicuboctahedron)
*Elongated square gyrobicupola
*Rubik's Snake - puzzle that can form a Rhombicuboctahedron "ball"
*The National Library of Belarus - its architectural main component has the shape of a rhombicuboctahedron.

References

* (Section 3-9)
*

External links

*
* [http://agutie.homestead.com/files/rhombicubocta.html Archimedes and the Rhombicuboctahedron] by Antonio Gutierrez from Geometry Step by Step from the Land of the Incas.
* [http://www.mathconsult.ch/showroom/unipoly/ The Uniform Polyhedra]
* [http://www.georgehart.com/virtual-polyhedra/vp.html Virtual Reality Polyhedra] The Encyclopedia of Polyhedra
* " [http://demonstrations.wolfram.com/RhombicuboctahedronStar/ Rhombicuboctahedron Star] " by Sándor Kabai, The Wolfram Demonstrations Project.
* [http://www.faust.fr.bw.schule.de/mhb/flechten/rhku/indexeng.htm Rhombicuboctahedron: paper strips for plaiting]
* [http://www.lifeisastoryproblem.org/explore/net_rhombicuboctahedron.pdf Printable Net of a Rhombicuboctahedron] [http://www.lifeisastoryproblem.org Life is a Story Problem.org]