Noun
The pentagonal dodecahedron, a common form of pyrite.
Source: Webster's dictionaryGeometric freedom The pyritohedron has a geometric degree of freedom with limiting cases of a cubic convex hull at one limit of colinear edges, and a rhombic dodecahedron as the other limit as 6 edges are degenerated to length zero. Source: Internet
One of the forms, called the pyritohedron (named for the group of minerals of which it is typical) has twelve pentagonal faces, arranged in the same pattern as the faces of the regular dodecahedron. Source: Internet
The rhombic dodecahedron can be seen as a degenerate pyritohedron where the 6 special edges have been reduced to zero length, reducing the pentagons into rhombic faces. Source: Internet
The faces of the pyritohedron are, however, not regular, so the pyritohedron is also not regular. Source: Internet