Triangular faces
Of the 13 Catalan solids, 7 have triangular faces. These are of the form Vp.q.r, where p, q and r take their values among 3, 4, 5, 6, 8 and 10. The angles , and can be computed in the following way. Put , , and put
- .
Then
- ,
- .
For and the expressions are similar of course. The dihedral angle can be computed from
- .
Applying this, for example, to the disdyakis triacontahedron (, and , hence , and , where is the golden ratio) gives and .
Quadrilateral faces
Of the 13 Catalan solids, 4 have quadrilateral faces. These are of the form Vp.q.p.r, where p, q and r take their values among 3, 4, and 5. The angle can be computed by the following formula:
- .
From this, , and the dihedral angle can be easily computed. Alternatively, put , , . Then and can be found by applying the formulas for the triangular case. The angle can be computed similarly of course.
The faces are kites, or, if , rhombi.
Applying this, for example, to the deltoidal icositetrahedron (, and ), we get .
Metric properties
For a Catalan solid let be the dual with respect to the midsphere of . Then is an Archimedean solid with the same midsphere. Denote the length of the edges of by . Let be the inradius of the faces of , the midradius of and , the inradius of , and the circumradius of . Then these quantities can be expressed in and the dihedral angle as follows:
- ,
- ,
- ,
- .
These quantities are related by , and .
As an example, let be a cuboctahedron with edge length . Then is a rhombic dodecahedron. Applying the formula for quadrilateral faces with and gives , hence , , , .
All vertices of of type lie on a sphere with radius given by
- ,
and similarly for .
Dually, there is a sphere which touches all faces of which are regular -gons (and similarly for ) in their center. The radius of this sphere is given by
- .
These two radii are related by . Continuing the above example: and , which gives , , and .
If is a vertex of of type , an edge of starting at , and the point where the edge touches the midsphere of , denote the distance by . Then the edges of joining vertices of type and type have length . These quantities can be computed by
- ,
and similarly for . Continuing the above example: , , , , so the edges of the rhombic dodecahedron have length .
The dihedral angles between -gonal and -gonal faces of satisfy
- .
Finishing the rhombic dodecahedron example, the dihedral angle of the cuboctahedron is given by .