The snub disphenoid, also known as the siamese dodecahedron, is one of the 92 Johnson solids (J84). It consists of 4+8 triangles as faces.

Snub disphenoid
Bowers style acronymSnadow
Faces4+8 triangles
Vertex figures4 rhombi, edge length 1
 4 pentagons, edge length 1
Measures (edge length 1)
Volume≈ 0.85949
Central density1
Number of external pieces12
Level of complexity9
Related polytopes
DualElongated gyrobifastigium
ConjugateSnub disphenoid
Abstract & topological properties
Flag count72
Euler characteristic2
Symmetry(B2×A1)/2, order 8

It can be constructed from a tetrahedron, seen as a digonal antiprism or disphenoid, by expanding the two halves outward and inserting a set of 8 triangles in between the halves.

Coordinates Edit

Coordinates for a snub disphenoid of unit edge length are given by

  •  ,
  •  ,
  •  ,
  •  ,

where r, s and t are given in terms of the unique positive root q ≈ 0.16902 of




With these coordinates, it's possible to calculate the volume of a snub disphenoid with unit edge length as ξ ≈ 0.85949, where ξ is the unique positive root of the polynomial


Related polyhedra Edit

The snub disphenoid can be considered to be the digonal case in the family of snub antiprisms. The snub triangular antiprism is the regular icosahedron, and the snub square antiprism is another Johnson solid. No other convex members of this family can be made to have all regular faces, though nonconvex regular-faced cases do exist.

If each square of a square antiprism are turned into two triangles, the result is a snub disphenoid. If only one square is turned into triangles, the result is a biaugmented triangular prism.

In vertex figures Edit

The snub disphenoid appears as the vertex figure of the nonuniform 13-5 step prism. This vertex figure has an edge length of 1, and has no corealmic realization, because the Johnson snub disphenoid has no circumscribed sphere.

External links Edit

References Edit

  1. Wolfram Research, Inc. (2021). "Wolfram|Alpha Knowledgebase". Champaign, IL. MinimalPolynomial[PolyhedronData[{"Johnson", 84}, "Volume"], x] Cite journal requires |journal= (help)