pyritohedron

from The Century Dictionary.

• noun In crystallography, a pentagonal dodecahedron (see dodecahedron); a solid contained by twelve pentagons: a common form with pyrite, whence the name. It is the hemihedral form of the tetrahexahedron.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Crystallog.) The pentagonal dodecahedron, a common form of pyrite.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun mathematics an irregular dodecahedron, consisting of identical but irregular pentagons
• noun the shape of a crystal of pyrite