In geometry, the small hexagrammic hexecontahedron is a nonconvex isohedral polyhedron. It is the dual of the small retrosnub icosicosidodecahedron. It is partially degenerate, having coincident vertices, as its dual has coplanar triangular faces.
Geometry Its faces are hexagonal stars with two short and four long edges. Denoting the golden ratio by ϕ {\displaystyle \phi } and putting ξ = 1 4 + 1 4 1 + 4 ϕ ≈ 0.933 380 199 59 {\displaystyle \xi ={\frac {1}{4}}+{\frac {1}{4}}{\sqrt {1+4\phi }}\approx 0.933\,380\,199\,59} , the stars have five equal angles of arccos ( ξ ) ≈ 21.031 988 967 51 ∘ {\displaystyle \arccos(\xi )\approx 21.031\,988\,967\,51^{\circ }} and one of 360 ∘ − arccos ( ϕ − 2 ξ − ϕ − 1 ) ≈ 254.840 055 162 43 ∘ {\displaystyle 360^{\circ }-\arccos(\phi ^{-2}\xi -\phi ^{-1})\approx 254.840\,055\,162\,43^{\circ }} . Each face has four long and two short edges. The ratio between the edge lengths is
1 / 2 − 1 / 2 × ( 1 − ξ ) / ( ϕ 3 − ξ ) ≈ 0.428 986 992 12 {\displaystyle 1/2-1/2\times {\sqrt {(1-\xi )/(\phi ^{3}-\xi )}}\approx 0.428\,986\,992\,12} . The dihedral angle equals arccos ( ξ / ( 1 + ξ ) ) ≈ 61.133 452 273 64 ∘ {\displaystyle \arccos(\xi /(1+\xi ))\approx 61.133\,452\,273\,64^{\circ }} . Part of each face is inside the solid, hence is not visible in solid models.
References Wenninger, Magnus (1983), Dual Models, Cambridge University Press, ISBN 978-0-521-54325-5, MR 0730208
External links Weisstein, Eric W. "Small hexagrammic hexecontahedron". MathWorld.




