berylloid

from The Century Dictionary.

• noun A solid consisting of two twelve-sided pyramids placed base to base: so called because the planes of this form are common in crystals of beryl.

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

• noun (Crystallog.) A solid consisting of a double twelve-sided pyramid; -- so called because the planes of this form occur on crystals of beryl.

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

• noun a solid consisting of a double twelve-sided pyramid