Small triambic icosahedron

In geometry, the small triambic icosahedron is the dual to the uniform small ditrigonal icosidodecahedron. It is composed of 20 intersecting isogonal hexagon faces. It has 60 edges and 32 vertices, and Euler characteristic of −8.

If the intersected hexagonal faces are divided and new edges created, this figure becomes the triakis icosahedron. The descriptive name triakis icosahedron represents a topological construction starting with an icosahedron and adding short triangular pyramids. With the proper pyramid height this figure becomes a Catalan solid by the same name and the dual of the truncated dodecahedron.

The nonconvex uniform polyhedra great stellated dodecahedron and great dodecahedron, as viewed as surface topologies, can also be constructed as icosahedron with pyramids, the first with much tall pyramids, and the second with inverted ones.

It is also a uniform dual, and is the dual of the small ditrigonal icosidodecahedron. Other uniform duals which are also stellations of the icosahedron are the medial triambic icosahedron and the great triambic icosahedron.

As a stellation

This figure is also the first stellation of the icosahedron, and given as Wenninger model index 26.

This stellation is a popular subject for construction in modular origami, often made of thirty Sonobe units.

References

• Wenninger, Magnus (1974). Polyhedron Models. Cambridge University Press. ISBN 0-521-09859-9.  (p. 46, Model W₂₆, triakis icosahedron)
• Wenninger, Magnus (1983). Dual Models. Cambridge University Press. ISBN 0-521-54325-8.  (pp. 42–46, dual to uniform polyhedron W₇₀)
• Coxeter, Harold Scott MacDonald; Du Val, P.; Flather, H. T.; Petrie, J. F. (1999). The fifty-nine icosahedra (3rd ed.). Tarquin. ISBN 978-1-899618-32-3. MR676126  (1st Edn University of Toronto (1938))

External links

• Weisstein, Eric W., "Small triambic icosahedron" from MathWorld.