The trapezo-rhombic dodecahedron, also called the rhombo-trapezoidal dodecahedron, is a general dodecahedron consisting of six identical
rhombi and six identical isosceles
trapezoids. It is convex, space-filling,
and has
symmetry.

A skeleton based on projecting from along the symmetry axis and rotating the inner and central points
is illustrated above.

If the spheres of face-centered cubic packing are expanded until they fill up the gaps, they form a solid rhombic dodecahedron,
and if the spheres of hexagonal close packing
are expanded, they form the trapezo-rhombic dodecahedron (Steinhaus 1999, p. 206).

The trapezo-rhombic dodecahedron can be obtained from the rhombic dodecahedron by slicing in half and rotating the two halves with respect to each other. The lengths of the short
and long edges of the rotated dodecahedron have lengths 2/3 and 4/3 times the length
of the rhombic faces.

The top and bottom edge lengths of the constituent trapezoids are and , with side lengths (corresponding to the rhombi edge lengths)
of .
The acute angles of the trapezoids and rhombi therefore have angle measure of

Sloane, N. J. A. Sequence AA137914 in "The On-Line Encyclopedia of Integer Sequences."Steinhaus,
H. Mathematical
Snapshots, 3rd ed. New York: Dover, pp. 202-203, 1999.