# Triakis octahedron

Triakis octahedron :
| (Click here for rotating model) ||
| Type | Catalan solid |
| Coxeter diagram | |
| Conway notation | kO |
| Face type | V3.8.8 isosceles triangle |
| Faces | 24 |
| Edges | 36 |
| Vertices | 14 |
| Vertices by type | 8{3}+6{8} |
| Symmetry group | O$_h$, B$_3$, [4,3], (*432) |
| Rotation group | O, [4,3]$^+$, (432) |
| Dihedral angle | 147°21′00″ arccos(−⁠3 + 8√2/17⁠) |
| Properties | convex, face-transitive |
| Truncated cube (dual polyhedron) | Net |
In geometry, a triakis octahedron (or trigonal trisoctahedron or kisoctahedron) is an Archimedean dual solid, or a Catalan solid. Its dual is the truncated cube.
It can be seen as an octahedron with triangular pyramids added to each face; that is, it is the Kleetope of the octahedron. It is also sometimes called a trisoctahedron, or, more fully, trigonal trisoctahedron. Both names reflect that it has three triangular faces for every face of an octahedron. The tetragonal trisoctahedron is another name for the deltoidal icositetrahedron, a different polyhedron with three quadrilateral faces for every face of an octahedron.
This convex polyhedron is topologically similar to the concave stellated octahedron. They have the same face connectivity, but the vertices are at different relative distances from the center.
If its shorter edges have length of 1, its surface area and volume are:
    ${\begin{aligned}A&=3{\sqrt {7+4{\sqrt {2}}}}\\V&={\frac {3+2{\sqrt {2}}}{2}}\end{aligned}}$

## Cartesian coordinates

Let α = √2 − 1, then the 14 points (±α, ±α, ±α) and (±1, 0, 0), (0, ±1, 0) and (0, 0, ±1) are the vertices of a triakis octahedron centered at the origin.
The length of the long edges equals √2, and that of the short edges 2√2 − 2.
The faces are isosceles triangles with one obtuse and two acute angles. The obtuse angle equals arccos(⁠1/4⁠ − ⁠√2/2⁠) ≈ 117.20057038016° and the acute ones equal arccos(⁠1/2⁠ + ⁠√2/4⁠) ≈ 31.39971480992°.

## Orthogonal projections

The triakis octahedron has three symmetry positions, two located on vertices, and one mid-edge:
Orthogonal projections :
| Projective symmetry | [2] | [4] | [6] |
| Triakis octahedron | | | |
| Truncated cube | | | |

## Cultural references

* A triakis octahedron is a vital element in the plot of cult author Hugh Cook's novel The Wishstone and the Wonderworkers.

## Related polyhedra

The triakis octahedron is one of a family of duals to the uniform polyhedra related to the cube and regular octahedron.
Uniform octahedral polyhedra :
| Symmetry: [4,3], (*432) | Symmetry: [4,3], (*432) | Symmetry: [4,3], (*432) | Symmetry: [4,3], (*432) | Symmetry: [4,3], (*432) | Symmetry: [4,3], (*432) | Symmetry: [4,3], (*432) | [4,3]$^+$ (432) | [1$^+$,4,3] = [3,3] (*332) | [1$^+$,4,3] = [3,3] (*332) | [3$^+$,4] (3*2) |
| {4,3} | t{4,3} | r{4,3} r{3$^{1,1}$} | t{3,4} t{3$^{1,1}$} | {3,4} {3$^{1,1}$} | rr{4,3} s$_2${3,4} | tr{4,3} | sr{4,3} | h{4,3} {3,3} | h$_2${4,3} t{3,3} | s{3,4} s{3$^{1,1}$} |
| | | = | = | = | | | | = or | = or | = |
| Duals to uniform polyhedra |||||||||||
| V4$^3$ | V3.8$^2$ | V(3.4)$^2$ | V4.6$^2$ | V3$^4$ | V3.4$^3$ | V4.6.8 | V3$^4$.4 | V3$^3$ | V3.6$^2$ | V3$^5$ |
The triakis octahedron is a part of a sequence of polyhedra and tilings, extending into the hyperbolic plane. These face-transitive figures have (*n32) reflectional symmetry.
*n32 symmetry mutation of truncated tilings: t{n,3} vte :
| Symmetry *n32 [n,3] | Spherical | Spherical | Spherical | Spherical | Euclid. | Compact hyperb. | Compact hyperb. | Paraco. | Noncompact hyperbolic | Noncompact hyperbolic | Noncompact hyperbolic |
| Symmetry *n32 [n,3] | *232 [2,3] | *332 [3,3] | *432 [4,3] | *532 [5,3] | *632 [6,3] | *732 [7,3] | *832 [8,3]... | *∞32 [∞,3] | [12i,3] | [9i,3] | [6i,3] |
| Truncated figures | | | | | | | | | | | |
| Symbol | t{2,3} | t{3,3} | t{4,3} | t{5,3} | t{6,3} | t{7,3} | t{8,3} | t{∞,3} | t{12i,3} | t{9i,3} | t{6i,3} |
| Triakis figures | | | | | | | | | | | |
| Config. | V3.4.4 | V3.6.6 | V3.8.8 | V3.10.10 | V3.12.12 | V3.14.14 | V3.16.16 | V3.∞.∞ | | | |
The triakis octahedron is also a part of a sequence of polyhedra and tilings, extending into the hyperbolic plane. These face-transitive figures have (*n42) reflectional symmetry.
*n42 symmetry mutation of truncated tilings: n.8.8 vte :
| Symmetry *n42 [n,4] | Spherical | Spherical | Euclidean | Compact hyperbolic | Compact hyperbolic | Compact hyperbolic | Compact hyperbolic | Paracompact |
| Symmetry *n42 [n,4] | *242 [2,4] | *342 [3,4] | *442 [4,4] | *542 [5,4] | *642 [6,4] | *742 [7,4] | *842 [8,4]... | *∞42 [∞,4] |
| Truncated figures | | | | | | | | |
| Config. | 2.8.8 | 3.8.8 | 4.8.8 | 5.8.8 | 6.8.8 | 7.8.8 | 8.8.8 | ∞.8.8 |
| n-kis figures | | | | | | | | |
| Config. | V2.8.8 | V3.8.8 | V4.8.8 | V5.8.8 | V6.8.8 | V7.8.8 | V8.8.8 | V∞.8.8 |